Nov. 2012, Outstanding Student Paper Award, IWH2012　　　　　　　　　　　　　　　
Interpage crosstalk suppression by spatial spectrum diffusion and digital phase conjugate reconstruction
Atsushi Shibukawa;Atsushi Okamoto;Yuta Wakayama;Akihisa Tomita;Hisatoshi Funakoshi;Kunihiro Sato

Oct. 2012, ISOM2012 Best Student Paper Award　　　　　　　　　　　　　　　
38-Level Spatial Quadrature-Amplitude Modulation Recording with Double-Referential Holography
Keisuke Zukeran;Atsushi Okamoto;Masanori Takabayashi;Atsushi Shibukawa;Akihisa Tomita

2006, ISOM Excessent Student Award　　　　　　　　　　　　　　　

2005, Best Paper Award　　　　　　　　　　　　　　　

2005, Best Paper Award　　　　　　　　　　　　　　　

2001, General Research Award　　　　　　　　　　　　　　　
岡本 淳, Japan

Reduction of the two-photon temporal distinguishability for measurement-device-independent quantum key distribution
Haobo Ge, Akihisa Tomita, Atsushi Okamoto, Kazuhisa Ogawa
Optics Letters, 49, 4, 822, 822, Optica Publishing Group, 05 Feb. 2024, [Peer-reviewed]
Scientific journal, Measurement-device-independent quantum key distribution (MDI-QKD) has been proven to protect legitimate users from attacks against measurement devices. The MDI-QKD requires that the two photons arriving at the instrument be indistinguishable. Precise time control is required to eliminate the distinguishability due to differences in photon arrival times. In the conventional methods, the time difference between photons is measured at a measuring instrument (Charlie), and a control signal is transmitted to the users (Alice and Bob). However, this method requires a long feedback loop, and the control may become unstable for long-distance transmission. This article proposes a method in which the photon arrival time difference is detected and controlled at Charlie. The reference signal for the time control is generated by an optical frequency comb in synchronization with the quantum signal. Therefore, the quantum signal photons can also be synchronized by synchronizing the reference signal pulses. A proof-of-principle experiment confirmed that the time synchronization accuracy required for protocol execution could be obtained. This proposal simplifies the implementation of the MDI-QKD.

Maximum multiplexing number of mode diffusion multiplex communication using progressive phase conjugation　　　　　　　　　　　　　　　
Zeyu Shen, Atsushi Okamoto, Akihisa Tomita
33th International Symposium on Imaging, Sensing, and Optical Memory 2023(ISOM’2023), Mo-F-02, Nov. 2023, [Peer-reviewed]

Performance Improvement by Convolutional Neural Networks in Virtual Phase Conjugation-based Optical Tomography　　　　　　　　　　　　　　　
Yu Yamada, Atsushi Okamoto, Yuki Oyama, Akihisa Tomita
33th International Symposium on Imaging, Sensing, and Optical Memory 2023(ISOM’2023), Mo-B-01, Nov. 2023, [Peer-reviewed]

Improvement of Phase Modulation Accuracy in LCOS-based Wave Shaper by Division of Modulation Region　　　　　　　　　　　　　　　
Wang Jianglian, Atsushi Okamoto, Nobuhiro Yamagishi, Yuta Goto, Akihisa Tomita
33th International Symposium on Imaging, Sensing, and Optical Memory 2023(ISOM’2023), Mo-F-01, Nov. 2023, [Peer-reviewed]

Virtual Measurement Technology for Reduction of Inter-Layer Noise in Virtual Phase Conjugation based Optical Tomography　　　　　　　　　　　　　　　
Yuki Oyama, Atsushi Okamoto, Akihisa Tomita
33th International Symposium on Imaging, Sensing, and Optical Memory 2023(ISOM’2023), Tu-E-03, Nov. 2023, [Peer-reviewed]

Single-shot digital holography separating the real and imaginary parts of a signal beam in the rhombic region of the Fourier plane
Nobuhiro Yamagishi, Atsushi Okamoto, Akihisa Tomita
Optical Review, 30, 2, 217, 231, Springer Science and Business Media LLC, 28 Mar. 2023, [Peer-reviewed]
Scientific journal

Analysis of the Effects of the Two-Photon Temporal Distinguishability on Measurement-Device-Independent Quantum Key Distribution
Haobo Ge, Akihisa Tomita, Atsushi Okamoto, Kazuhisa Ogawa
IEEE Transactions on Quantum Engineering, 4, 1, 8, Institute of Electrical and Electronics Engineers (IEEE), 2023
Scientific journal

Spatial mode compensation technique using progressive phase conjugation
Zeyu Shen, Atsushi Okamoto, Shuanglu Zhang, Akihisa Tomita
Optical Review, Springer Science and Business Media LLC, 12 Sep. 2022, [Peer-reviewed]
Scientific journal

Influence of phase accuracy on mode compensation using progressive phase conjugation　　　　　　　　　　　　　　　
Zeyu Shen, Atsushi Okamoto, Akihisa Tomita
32th International Symposium on Imaging, Sensing, and Optical Memory 2022 (ISOM’22), P-IPDP-04, Aug. 2022, [Peer-reviewed]

Mode diffusion technique for crosstalk reduction in volume holographic mode exchanger　　　　　　　　　　　　　　　
Zhang Shuanglu, Atsushi Okamoto, Akihisa Tomita
32th International Symposium on Imaging, Sensing, and Optical Memory 2022 (ISOM’22), P-ITu-09, Aug. 2022, [Peer-reviewed]

Spatial-light-modulator-based optical-fiber joint switch for few-mode multicore fibers
Shuanglu Zhang, Atsushi Okamoto, Yuta Abe, Ryo Watanabe, Akihisa Tomita, Daiki Soma, Yuta Wakayama, Takehiro Tsuritani
Optics Express, 29, 24, 39096, 39096, Optica Publishing Group, 22 Nov. 2021, [Peer-reviewed]
Scientific journal, To realize simplified cost-efficient optical networks with routing flexibility and scaling potential, a spatial-light-modulator-based optical-fiber joint switch for few-mode multicore fibers is proposed herein, which can route all spatial channels together as a unit. Numerical simulations and experiments were performed, and the results show that the signal paths for a 6-mode 19-core fiber can be simultaneously switched to the target output ports using the proposed method, and the mode-field patterns of the diffracted light can be maintained after joint switching. Further, the maximum port crosstalk can be reduced considerably from -11.6 to -25.1 dB by changing the position of the output port in the proposed method.

Relationship Between Detector Accuracy and Measurement Quality in Superresolution Complex Amplitude Measurements Using Virtual Phase Conjugation　　　　　　　　　　　　　　　
Ryoya Imai, Atsushi Okamoto, Satoshi Kawashima, Kazuhisa Ogawa, Akihisa Tomita
12th International Conference on Optics-photonics Design & Fabrication“ODF '20 in 2021 Technical Digest, 01S1-04, Oct. 2021, [Peer-reviewed]

3D super-resolution projection using single-lens spatial cross-modulation method　　　　　　　　　　　　　　　
Xinruinan Zhang, Atsushi Okamoto, Hisatoshi Funakoshi, Akihisa Tomita
31th International Symposium on Imaging, Sensing, and Optical Memory 2021 (ISOM’21), Tu-D-03, Oct. 2021, [Peer-reviewed]

Improvement in Diffraction Efficiency of Volume Holographic Mode DeMultiplexer with Dual Wavelength method by Using Thick Medium　　　　　　　　　　　　　　　
Yuya Kuroda, Atsushi Okamoto, Akihisa Tomita, Taketoshi Takahata, Satoshi Shinada, Yuta Goto, Naoya Wada
31th International Symposium on Imaging, Sensing, and Optical Memory 2021 (ISOM’21), We-A-04, Oct. 2021, [Peer-reviewed]

Improvement of mode compensation accuracy using a random diffuser in progressive phase conjugation　　　　　　　　　　　　　　　
Zeyu Shen, Atsushi Okamoto, Shuanglu Zhang, Akihisa Tomita
31th International Symposium on Imaging, Sensing, and Optical Memory 2021 (ISOM’21), We-B-03, Oct. 2021, [Peer-reviewed]

Complex amplitude control technology for mode-multiplexing optical communication　　　　　　　　　　　　　　　
Atsushi Okamoto, Tomohiro Maeda, Taketoshi Takahata, Yuta Goto, Satoshi Shinada, Naoya Wada
02S4-05, Jun. 2021, [Peer-reviewed], [Invited]

Spatial mode exchange technique using volume holograms with a random optical diffuser for reduction of crosstalk
Shuanglu Zhang, Atsushi Okamoto, Taijun Shiba, Hotaka Hayashi, Kazuhisa Ogawa, Akihisa Tomita, Taketoshi Takahata, Satoshi Shinada, Yuta Goto, Naoya Wada
OPTICAL REVIEW, 28, 2, 181, 189, OPTICAL SOC JAPAN, Apr. 2021
English, Scientific journal, In mode-division multiplexing systems, the transmission quality is restricted by the differential mode delay (DMD). We previously proposed a spatial mode exchange technique using volume holograms (VHET) to reduce the DMD. VHET can be used for the exchange of multiple spatial modes with different transmission speeds using a single device. However, in VHET, incidents of cross-talk (XT) caused by non-target holograms severely degrade the exchange performance. To address this issue, we propose a spatial mode exchange technique that uses volume holograms in combination with a random optical diffuser. By scattering the intensity distribution of the signal beam uniformly using a random optical diffuser, high exchange performance can be attained due to the reduction in the influence of non-targeted holograms. We confirmed the basic operation of the proposed scheme by considering the crosstalk component coupled to the few-mode fiber in a mode-division multiplexing system. The simulation results show that the maximum XTs are significantly suppressed to - 15.8 dB.

Super-resolution Measurement By Virtual Phase Conjugation Using A Small Number Of Pixels For Optical Detection　　　　　　　　　　　　　　　
Satoshi Kawashima, Atsushi Okamoto, Kazuhisa Ogawa, Akihisa Tomita
30th International Symposium on Imaging, Sensing, and Optical Memory 2020 (ISOM’20), Mo-D-04, Nov. 2020, [Peer-reviewed]

Improving the reconstruction quality of spatial mode exchange technique by adjusting the diffusion angle of diffuser　　　　　　　　　　　　　　　
Zhang Shuanglu, Atsushi Okamoto, Kazuhisa Ogawa, Akihisa Tomita, Taketoshi Takahata, Satoshi Shinada, Yuta Goto, Naoya Wada
30th International Symposium on Imaging, Sensing, and Optical Memory 2020 (ISOM’20), Mo-C-01, Nov. 2020, [Peer-reviewed]

空間光変調器を用いた光波制御と光情報処理
岡本 淳, 前田 智弘, 舟越 久敏
電子情報通信学会論文誌 C, Vol.J103-C, 10, 412, 419, Sep. 2020, [Peer-reviewed], [Invited], [Lead author]
Japanese, Scientific journal, 45167129

Perspectives and Observations of Information Photonics using Optical Complex-Amplitude Control Technology
Atsushi OKAMOTO, Tomohiro MAEDA
The Journal of The Institute of Electrical Engineers of Japan, 140, 5, 299, 302, Institute of Electrical Engineers of Japan (IEE Japan), 01 May 2020, [Peer-reviewed], [Invited], [Lead author]
Japanese

State preparation robust to modulation signal degradation by use of a dual parallel modulator for high-speed BB84 quantum key distribution systems
Weiyang Zhang, Yu Kadosawa, Akihisa Tomita, Kazuhisa Ogawa, Atsushi Okamoto
Optics Express, 28, 9, 13965, 13965, The Optical Society, 27 Apr. 2020, [Peer-reviewed]
Scientific journal

Mode-selective switch for ROADM using volume holograms and spatial light modulator
Hotaka Hayashi, Atsushi Okamoto, Tomohiro Maeda, Taijun Shiba, Kazuhisa Ogawa, Akihisa Tomita, Taketoshi Takahata, Satoshi Shinada, Yuta Goto, Naoya Wada
Next-Generation Optical Communication: Components, Sub-Systems, and Systems IX, SPIE, 31 Jan. 2020
International conference proceedings

Spatial mode exchange technique using volume holograms with a random optical diffuser to reduce modal cross-talks
Zhang Shuanglu, Atsushi Okamoto, Taijun Shiba, Hotaka Hayashi, Kazuhisa Ogawa, Akihisa Tomita, Taketoshi Takahata, Satoshi Shinada, Yuta Goto, Naoya Wada
Next-Generation Optical Communication: Components, Sub-Systems, and Systems IX, SPIE, 31 Jan. 2020
International conference proceedings

Three-dimensional tomographic imaging and quantitative phase measurement using virtual phase conjugation
Satoshi Kawashima, Atsushi Okamoto, Tomohiro Maeda, Kazuhisa Ogawa, Akihisa Tomita, Ryusuke Osaki, Naoki Hayashi
Progress in Biomedical Optics and Imaging - Proceedings of SPIE, 11245, SPIE, 2020
English, International conference proceedings, We have proposed virtual-phase-conjugation-based optical tomography (VPC-OT) using a virtual phase conjugation technology for single-shot and three-dimensional optical tomography. In VPC-OT, a random-spatial-phase-modulated probe beam is irradiated to the sample to be measured, and the complex amplitude of the signal composed of a superimposition of light reflected from each layer of the sample is measured. A three-dimensional tomogram of intensity and phase is obtained by reproducing the measured complex amplitude using a phase conjugate wave in a virtual optical system built in a computer. At this time, by changing the parameters of the virtual optical system, it becomes possible to obtain information of various tomographic planes from the data obtained with a single measurement. In the ideal virtual phase conjugate reproduction process, free space propagation can be assumed
however, in the actual measurement, due to the distortion of the waves and the surroundings of the sample to be measured, a mismatch will occur in modulation and demodulation, and the separation accuracy between different tomographic planes would be degraded. We perform an experiment to clarify the characteristics of VPC-OT in this situation. In this experiment, three-dimensional optical tomography is performed using an etching glass having a periodic structure of 30 μm as a sample, and the phase distribution is measured quantitatively. Furthermore, by placing a cover glass in front of the object and performing the same measurement, we discuss the characteristics and performance of VPC-OT when there is an optical distortion around the sample to be measured.

Collective measurement of DMD in 6-mode 19-core fiber using low-coherence digital holography
Yuta Abe, Atsushi Okamoto, Kazuhisa Ogawa, Akihisa Tomita, Daiki Soma, Yuta Wakayama, Takehiro Tsuritani
Proceedings of SPIE - The International Society for Optical Engineering, 11309, SPIE, 2020
English, International conference proceedings, In the space division multiplexing system, differential mode delay (DMD) is an essential parameter for transmission quality and signal processing. In this paper, we proposed the collective measurement method for the DMD of each core in fewmode multi-core fiber (FM-MCF) using low-coherence digital holography (LCDH). In the conventional method, given that the DMD of each core needs to be measured individually, the number of measurements increases in proportion to the number of cores, which causes fluctuation of the measurement conditions. In contrast, the proposed method reduces the measurement time and realizes the accurate measurement under the same conditions for all cores. We experimentally demonstrate the proposed method by using 6-mode 19-core fiber as a fiber under test. As a result, DMD values were successfully measured for all 19 cores.

Enhancement of Power Efficiency in Volume Holographic Mode (De-)multiplexer with Dual-Wavelength Method
Yuta Goto, Atsushi Okamoto, Hotaka Hayashi, Satoshi Shinada, Taketoshi Takahata, Naoya Wada
OSA Advanced Photonics Congress (AP) 2020 (IPR, NP, NOMA, Networks, PVLED, PSC, SPPCom, SOF), OSA, 2020
International conference proceedings

Wavefront superposition method for accurate and efficient mode conversion　　　　　　　　　　　　　　　
Tomohiro Maeda, Atsushi Okamoto, Kazuhisa Ogawa, Akihisa Tomita
Applied Optics, 58, 25, 6899, 6905, Aug. 2019, [Peer-reviewed]
English, Scientific journal

Highly Accurate Mode Conversion Using Iterative Spatial Cross Modulation.　　　　　　　　　　　　　　　
Kazuhisa OgawaMaeda, T, Okamoto, A, Ogawa, K, Tomita, A, Wakayama, Y, Tsuritani, T
2019 24th OptoElectronics and Communications Conference (OECC) and 2019 International Conference on Photonics in Switching and Computing (PSC), 1, 3, Jul. 2019, [Peer-reviewed]
English, International conference proceedings

Characterization of Spatial-Mode Demultiplexer using 1550-nm-band Angularly Multiplexed Volume Holograms.
Satoshi Shinada, Taijun Shiba, Tomohiro Maeda, Taketoshi Takahata, Atsushi Okamoto, Naoya Wada
2019 24th OptoElectronics and Communications Conference (OECC) and 2019 International Conference on Photonics in Switching and Computing (PSC)(OECC/PSC), 1, 3, IEEE, 2019
International conference proceedings

Experimental implementation of multiplexing/demultiplexing in digital images using virtual phase conjugation for holographic data storage　　　　　　　　　　　　　　　
Yuta Goto, Atsushi Okamoto, Masanori Takabayashi, Kazuhisa Ogawa, Akihisa Tomita
Optical Review, 25, 5, 549, 554, Oct. 2018, [Peer-reviewed]
English, Scientific journal

Mode conversion based on dual-phase modulation utilizing interference of two-phase-modulated beams　　　　　　　　　　　　　　　
Tomohiro Maeda, Atsushi Okamoto, Kazuhisa Ogawa, Akihisa Tomita, Yuta Wakayama, Takehiro Tsuritani
Optical Review, 25, 6, 734, 742, Oct. 2018, [Peer-reviewed]
English, Scientific journal

Tracking quantum error correction
Fukui Kosuke, Tomita Akihisa, Okamoto Atsushi
PHYSICAL REVIEW A, 98, 2, 22 Aug. 2018, [Peer-reviewed]

High-Threshold Fault-Tolerant Quantum Computation with Analog Quantum Error Correction
Fukui Kosuke, Tomita Akihisa, Okamoto Atsushi, Fujii Keisuke
PHYSICAL REVIEW X, 8, 2, 25 May 2018, [Peer-reviewed]

Virtual phase conjugation based optical tomography for single-shot three-dimensional imaging　　　　　　　　　　　　　　　
Yuta Goto, Atsushi Okamoto, Atsushi Shibukawa, Kazuhisa Ogawa, Akihisa Tomita
Optics Express, 26, 4, 3779, 3790, Feb. 2018, [Peer-reviewed]
English, Scientific journal

Volume holographic spatial mode demultiplexer with a dual-wavelength method
Shimpei Shimizu, Atsushi Okamoto, Fumiya Mizukawa, Kazuhisa Ogawa, Akihisa Tomita, Taketoshi Takahata, Satoshi Shinada, Naoya Wada
Applied Optics, 57, 2, 146, 153, OSA - The Optical Society, 10 Jan. 2018, [Peer-reviewed]
English, Scientific journal, Volume holographic demultiplexers (VHDMs) provide spatial mode demultiplexing using simple optical systems. However, applying VHDM to practical optical communication systems is difficult, as typical holographic media have no sensitivity in the infrared region, which includes optical transmission bands. In this paper, we propose a VHDM scheme combined with a dual-wavelength method (DWM). Using the DWM, VHDMs are able to perform mode demultiplexing in the optical transmission bands. We experimentally demonstrated the basic operation of our proposal using experiments performed at an 850-nm wavelength. In addition, we performed numerical simulations to investigate the application of VHDM to the C-band.

Fundamental demonstration of mode-group demultiplexing technique based on volume holographic demultiplexer
Shimpei Shimizu, Atsushi Okamoto, Fumiya Mizukawa, Kazuhisa Ogawa, Akihisa Tomita, Taketoshi Takahata, Satoshi Shinada, Naoya Wada
22nd Microoptics Conference, MOC 2017, 2017-, P-62, 260, 261, Institute of Electrical and Electronics Engineers Inc., 02 Jan. 2018, [Peer-reviewed]
English, International conference proceedings, We demonstrated the mode-group demultiplexing technique based on a volume holographic demultiplexer (VHDM) for mode-group division multiplexing transmission using multi-mode fibers. In the experiment, the VHDM achieved the separating of three mode-group channels with a single holographic recording medium. Thus, the modal cross-talk was obtained as -14.7 dB.

Compensation of optical aberration for improvement of image quality in virtual-phase-conjugation based optical tomography
Yuta Goto, Atsushi Okamoto, Kazuhisa Ogawa, Akihisa Tomita
22nd Microoptics Conference, MOC 2017, 2017-, PD5, 358, 359, Institute of Electrical and Electronics Engineers Inc., 02 Jan. 2018, [Peer-reviewed]
English, International conference proceedings, We propose virtual-phase-conjugation based optical tomography (VPC-OT) incorporated with the compensation of the optical aberration for improving the imaging quality. The compensation scheme is implemented by optically measuring the transmission function of the beam propagation. Then, we confirmed that this scheme greatly improves the signal level of VPC-OT.

Selective mode conversion using dual-phase modulation
Tomohiro Maeda, Atsushi Okamoto, Kazuhisa Ogawa, Akihisa Tomita, Yuta Wakayama, Takehiro Tsuritani
22nd Microoptics Conference, MOC 2017, 2017-, C-4, 68, 69, Institute of Electrical and Electronics Engineers Inc., 02 Jan. 2018, [Peer-reviewed]
English, International conference proceedings, We propose a selective mode conversion method using dual-phase modulation which performs the full-complex amplitude modulation by use of two phase-type spatial light modulators. In the experiment, the crosstalk to undesired spatial mode was supressed less than -21.2 dB for the 4-LP modes of a few-mode fiber.

Selective spatial mode attenuator using phase-intensity-phase modulation toward mode-division multiplexing transmission
Zihan Zhou, Atsushi Okamoto, Shimpei Shimizu, Akihisa Tomita, Kazuhisa Ogawa, Yuta Wakayama, Takehiro Tsuritani
Proceedings of SPIE - The International Society for Optical Engineering, 10561, 10561-15, SPIE, 2018, [Peer-reviewed]
English, International conference proceedings, In a mode division multiplexing (MDM) transmission using few-mode fibers (FMFs), differential modal gain (DMG) in amplifiers and mode dependent loss (MDL) cause deterioration in signal quality. Therefore, the techniques which selectively attenuate multiplexed modes and equalize optical powers among mode channels are required for a long-haul MDM transmission. In this paper, we propose a selective mode attenuator using phase-intensity-phase (PIP) modulation. The PIP modulation, consisting of a cascade of two phase and one intensity modulation masks connected by optical Fourier transforms (OFTs), makes it possible to selectively attenuate multiplexed mode channels with high accuracy. In the proposed method, the intensity distributions of spatial modes are converted by the phase modulation and OFT, before doing attenuation by intensity mask located between the two phase masks. Due to the action of a pair of phase masks having phase conjugate relations, accurately selective mode attenuation can be performed even if the number of modes is increased over three. To confirm the basic operation of the proposed method, we perform a numerical simulation for power equalization among six spatial modes (LP01, LP11a, LP11b, LP21a, LP21b, and LP02) having different powers. The phase and intensity masks are designed by using simulated annealing. Moreover, we also evaluate modal crosstalk (MXT) characteristics and the wavelength dependence of the equalization in C-band. The results show that the optical powers of all modes are successfully equalized for any wavelengths and the MXT smaller than -25 dB were achieved between all modes.

Measurement of differential mode delay using reference-free low-coherence digital holography
Shogo Hoshino, Atsushi Okamoto, Yuta Goto, Kazuhisa Ogawa, Akihisa Tomita, Yuta Wakayama, Takehiro Tsuritani
Proceedings of SPIE - The International Society for Optical Engineering, 10561, 10561-12, SPIE, 2018, [Peer-reviewed]
English, International conference proceedings, In the mode division multiplexing (MDM) system, differential mode delay (DMD) restricts the quality of transmission. Thus, it is necessary to precisely measure DMD for compensation and system design. The DMD measurement method using low-coherence digital holography (LCDH) has been proposed. This method can obtain not only accurate DMD but also spatial mode fields. However, in this method, an SMF as the reference arm is needed and its length should be particularly adjusted to a fiber under test (FUT) for low-coherence interferometric measurement. We propose a DMD measurement method by reference-free low-coherence digital holography (RF-LCDH). In the proposed method, we generate a new optical path from the light emitted from the FUT, which is regard as internal-reference light. The proposed method enables us to obtain DMD and spatial mode fields without the SMF as the reference arm by using internal-reference light. In the experiment, we measured DMD of a 10-mode fiber to confirm the basic operation of the proposed method. As the result, without using additional SMFs for reference arm, the proposed method achieved the measurement accuracy which was in good agreement with that of the conventional method.

Analog Quantum Error Correction with Encoding a Qubit into an Oscillator
Kosuke Fukui, Akihisa Tomita, Atsushi Okamoto
PHYSICAL REVIEW LETTERS, 119, 18, 180507-1, 180507-4, AMER PHYSICAL SOC, Nov. 2017, [Peer-reviewed]
English, Scientific journal, To implement fault-tolerant quantum computation with continuous variables, Gottesman-Kitaev-Preskill (GKP) qubits have been recognized as an important technological element. However, the analog outcome of GKP qubits, which includes beneficial information to improve the error tolerance, has been wasted, because the GKP qubits have been treated as only discrete variables. In this Letter, we propose a hybrid quantum error correction approach that combines digital information with the analog information of the GKP qubits using a maximum-likelihood method. As an example, we demonstrate that the three-qubit bit-flip code can correct double errors, whereas the conventional method based on majority voting on the binary measurement outcome can correct only a single error. As another example, we show that a concatenated code known as Knill's C-4/C-6 code can achieve the hashing bound for the quantum capacity of the Gaussian quantum channel (GQC). To the best of our knowledge, this approach is the first attempt to draw both digital and analog information to improve quantum error correction performance and achieve the hashing bound for the quantum capacity of the GQC.

Digital image multiplexing/demultiplexing method using spatial spectral diffusion and virtual phase conjugation technique for reduction of dynamic range consumption in holographic medium　　　　　　　　　　　　　　　
Yuta Goto, Atsushi Okamoto, Masanori Takabayashi, Kazuhisa Ogawa, Akihisa Tomita
Japanese Journal of Applied Physics, 56, 9S, 09NA07-1, 09NA07-8, Aug. 2017, [Peer-reviewed]
English, Scientific journal

Spatial mode demultiplexing technique using angularly multiplexed volume holograms with a phase plate
Shimpei Shimizu, Atsushi Okamoto, Fumiya Mizukawa, Kazuhisa Ogawa, Akihisa Tomita, Taketoshi Takahata, Satoshi Shinada, Naoya Wada
Japanese Journal of Applied Physics, 56, 98, 09NA05-1, 09NA05-5, Institute of Physics, Aug. 2017, [Peer-reviewed]
English, Scientific journal, In this paper, we propose a spatial mode demultiplexing technique that uses a volume holographic demultiplexer (VHDM) with a phase plate. The VHDM can separate the multiplexed spatial modes with a single device by using angularly multiplexed volume holograms. In the VHDM, modal cross-talks, which are called inter-page cross-talks in the holographic data storages, are generated, and hence the separation performance of the VHDM is degraded by the intensity overlap between spatial modes. Therefore, we propose a novel scheme wherein phase modulation with a phase plate is added to the conventional scheme. The proposed scheme can achieve high separation performance by modulating the phase of spatial modes to reduce the intensity overlap. In this study, we demonstrated the basic operation of the proposed method for a specific linearly polarized mode group. The separation performance of the VHDM was observed to be markedly improved by the proposed method.

Improvement of Conversion Accuracy in Volume Holographic Mode-Demultiplexing Converter Using Shaped Beams　　　　　　　　　　　　　　　
Fumiya Mizukawa, Atsushi Okamoto, Yuta Goto, Shimpei Shimizu, Kazuhisa Ogawa, Akihisa Tomita
International Workshop on Holography and Related Technologies 2017 (IWH2017), P2, 2017, [Peer-reviewed]
English, International conference proceedings

Design of Complex Amplitude Modulation for Suppressing Optical Loss in Mode Conversion by Considering Radiation Modes　　　　　　　　　　　　　　　
Tomohiro Maeda, Atsushi Okamoto, Kazuhisa Ogawa, Akihisa Tomita
International Workshop on Holography and Related Technologies 2017 (IWH2017), P9, 2017, [Peer-reviewed]
English, International conference proceedings

Multiplexing and Demultiplexing of Digital Images using Virtual Phase Conjugation for High-Density Holographic Data Storage　　　　　　　　　　　　　　　
Yuta Goto, Atsushi Okamoto, Kazuhisa Ogawa, Akihisa Tomita
International Workshop on Holography and Related Technologies 2017 (IWH2017), P10, 2017, [Peer-reviewed]
English, International conference proceedings

Spatial Mode Separation and Conversion Technique Using Volume Hologram with a Random Optical Diffuser　　　　　　　　　　　　　　　
Fumiya Mizukawa, Atsushi Okamoto, Yuta Goto, Shimpei Shimizu, Kazuhisa Ogawa, Akihisa Tomita
27th International Symposium on Imaging, Sensing, and Optical Memory 2017 (ISOM’17), Tu-J-35, 2017, [Peer-reviewed]
English, International conference proceedings

Experiment on Spatial Mode Demultiplexing Technique Using Cascaded Volume Hologram　　　　　　　　　　　　　　　
Shimpei Shimizu, Atsushi Okamoto, Fumiya Mizukawa, Kazuhisa Ogawa, Akihisa Tomita, Taketoshi Takahata, Satoshi Shinada, Naoya Wada
27th International Symposium on Imaging, Sensing, and Optical Memory 2017 (ISOM’17), Tu-J-25, 2017, [Peer-reviewed]
English, International conference proceedings

Multiplexing Technique using Virtual Phase Conjugation for High-Density Holographic Data Storage Systems　　　　　　　　　　　　　　　
Yuta Goto, Atsushi Okamoto, Masanori Takabayashi, Akihisa Tomita
27th International Symposium on Imaging, Sensing, and Optical Memory 2017 (ISOM’17), Tu-PP-02, 2017, [Peer-reviewed]
English, International conference proceedings

Optimization of Volume Holographic Spatial Mode Demultiplexer with a Phase Plate Using Simulated Annealing　　　　　　　　　　　　　　　
Shimpei Shimizu, Atsushi Okamoto, Fumiya Mizukawa, Kazuhisa Ogawa, Akihisa Tomita, Taketoshi Takahata, Satoshi Shinada, Naoya Wada
International Workshop on Holography and Related Technologies 2017 (IWH2017), 23a3, 2017, [Peer-reviewed]
English, International conference proceedings

Experiment on spatial mode separation and conversion technique using volume hologram
Fumiya Mizukawa, Atsushi Okamoto, Yuta Goto, Shimpei Shimizu, Kazuhisa Ogawa, Akihisa Tomita
7th EOS Topical Meeting on Optical Microsystems (OµS’17), 41, 35, 157, 161, 映像情報メディア学会, 2017, [Peer-reviewed]
English, International conference proceedings

Experiment on spatial mode demultiplexer based on angularly multiplexed volume hologram at 850 nm wavelength with dual-wavelength method　　　　　　　　　　　　　　　
himpei Shimizu, Atsushi Okamoto, Fumiya Mizukawa, Kazuhisa Ogawa, Akihisa Tomita, Taketoshi Takahata, Satoshi Shinada, Naoya Wada
7th EOS Topical Meeting on Optical Microsystems (OµS’17), 22, 2017, [Peer-reviewed]
English, International conference proceedings

Depth-resolution characterization of optical tomography using virtual phase conjugation　　　　　　　　　　　　　　　
Yuta Goto, Atsushi Okamoto, Atsushi Shibukawa, Kazuhisa Ogawa, Akihisa Tomita, Kunihiro Sato
7th EOS Topical Meeting on Optical Microsystems (OµS’17), 5, 2017, [Peer-reviewed]
English, International conference proceedings

Intensity fluctuation of a gain-switched semiconductor laser for quantum key distribution systems
Kensuke Nakata, Akihisa Tomita, Mikio Fujiwara, Ken-ichiro Yoshino, Akio Tajima, Atsushi Okamoto, Kazuhisa Ogawa
OPTICS EXPRESS, 25, 2, 622, 634, OPTICAL SOC AMER, Jan. 2017, [Peer-reviewed]
English, Scientific journal, Security certification of quantum key distribution (QKD) systems under practical conditions is necessary for social deployment. This article focused on the transmitter, and, in particular, investigated the intensity fluctuation of the optical pulses emitted by a gain-switched semiconductor laser used in QKD systems implementing decoy-BB84 protocol. A large intensity fluctuation was observed for low excitation, showing strong negative correlation between the adjacent pulses, which would affect the final key rate. The fluctuation decreased and the correlation disappeared as excitation increased. Simulation with rate equations successfully reproduced the experimental results and revealed that the large fluctuation originates from an intrinsic instability of gain-switched lasers driven periodically at a rate comparable to the inverse of carrier lifetime, as in GHz-clock QKD systems. Methods for further reduction of the intensity fluctuation were also discussed. (C) 2017 Optical Society of America

Multi-Layered Holographic Memory using Virtual Phase Conjugation　　　　　　　　　　　　　　　
Yuta Goto, Atsushi Okamoto, Kazuhisa Ogawa, Akihisa Tomita, Kunihiro Sato
Technical Digest of the International Workshop on Holography 2016 (IWH 2016), 60, Nov. 2016, [Peer-reviewed]
English, International conference proceedings

Phase measurement of a tilted plane mirror using the derivative estimation of a single hologram　　　　　　　　　　　　　　　
Jin Nozawa, Atsuhshi Okamoto, Yasuyuki Kuno, Masataka Toda, Kazuhisa Ogawa, Akihisa Tomita
Technical Digest of the International Workshop on Holography 2016 (IWH 2016), 17, Nov. 2016, [Peer-reviewed]
English, International conference proceedings

Performance Evaluation of High Speed Full Motion Simulator for Holographic Memory Based on 3D FFT-BPM with GPU Acceleration　　　　　　　　　　　　　　　
Hisatoshi Funakoshi, Atsushi Okamoto, Satoshi Honma
Technical Digest of International Symposium on Optical Memory 2016 (ISOM 2016), Tu-J-03, Oct. 2016, [Peer-reviewed]
English, International conference proceedings

Accuracy evaluation of phase shifting digital holography using virtual interferogram-generation algorithm　　　　　　　　　　　　　　　
Jin Nozawa, Atsuhshi Okamoto, Kazuhisa Ogawa, Akihisa Tomita, Kunihiro Sato
Technical Digest of International Symposium on Optical Memory 2016 (ISOM 2016), Tu-J-17, Oct. 2016, [Peer-reviewed]
English, International conference proceedings

Multiplexing Technique using Virtual Phase Conjugation for High-Density Holographic Data Storage Systems　　　　　　　　　　　　　　　
OKAMOTO Atsushi
Yuta Goto, Atsushi Okamoto, Masanori Takabayashi, and Akihisa Tomita, We-L-03, Oct. 2016, [Peer-reviewed]
English, International conference proceedings

Spatial Mode Separation and Interconversion Using Volume Hologram　　　　　　　　　　　　　　　
Fumiya Mizukawa, Atsushi Okamoto, Yuta Goto, Shimpei Shimizu, Satoshi Honma, Kazuhisa Ogawa, Akihisa Tomita
Technical Digest of International Symposium on Optical Memory 2016 (ISOM 2016), Tu-I-04, Oct. 2016, [Peer-reviewed]
English, International conference proceedings

Effective Mode Demultiplexing Technique Using Angularly Multiplexed Volume Holograms with a Phase Plate　　　　　　　　　　　　　　　
Shimpei Shimizu, Atsushi Okamoto, Fumiya Mizukawa, Taketoshi Takahata, Shusaku Noda, Naoya Wada, Kazuhisa Ogawa, Akihisa Tomita
Technical Digest of International Symposium on Optical Memory 2016 (ISOM 2016), Tu-I-03, Oct. 2016, [Peer-reviewed]
English, International conference proceedings

Reference-free holographic diversity interferometry via iterative measurements for high accuracy phase detection
Yuta Goto, Atsushi Okamoto, Yuta Wakayama, Kazuhisa Ogawa, Jin Nozawa, Akihisa Tomita, Takehiro Tsuritani
OPTICS EXPRESS, 24, 21, 24739, 24749, OPTICAL SOC AMER, Oct. 2016, [Peer-reviewed]
English, Scientific journal, To obtain a phase distribution without the use of an optical path besides an object beam, a reference-free holographic diversity interferometry (RF-HDI) has been proposed. Although the RF-HDI can generate an internal reference beam from the object beam, the method has a problem of measurement accuracy due to insufficient power of the internal reference beam. To solve the problem, we newly propose a RF-HDI via iterative measurements. Our method improves the measurement accuracy by utilizing iterative measurements and feedback of each obtained phase image to the measurement system. In the experiment, the phase image, which has a random pattern, can be measured as an object beam with a higher accuracy than in the conventional RF-HDI. To support this result, we also evaluated the wavefront accuracy and optical power efficiency of an internal reference beam in this method. As a result, we verified that our method enables us to generate an internal reference beam that has the wavefront of a near single plane wave and a higher power efficiency than the conventional RF-HDI. In addition, our method can be applied to measurement for the modal content in an optical fiber, atmosphere turbulence, etc., where it is difficult to prepare an external reference beam with a high coherency. (C) 2016 Optical Society of America

Virtual interferogram-generation algorithm for robust complex amplitude measurement using two interferograms
Jin Nozawa, Atsushi Okamoto, Kazuhisa Ogawa, Akihisa Tomita
OPTICS EXPRESS, 24, 21, 24002, 24017, OPTICAL SOC AMER, Oct. 2016, [Peer-reviewed]
English, Scientific journal, We propose a virtual interferogram-generation algorithm using two interferograms. This algorithm can measure a complex amplitude of a signal beam with high accuracy even when its intensity is greater than the intensity of a reference beam. Unlike the conventional algorithm that uses two interferograms, our algorithm can compute measurements when the phase shift of interferograms in not equal to pi/2. Our method generates two phase-shifted holograms in a computer by capturing the intensities of two signal beams, two reference beams, and two interferograms. The complex amplitude of a signal beam is calculated by four interference patterns, two holograms, and two interferograms. The proposed algorithm can drastically suppress the calculation error caused by the smaller value between the intensity of the reference beam and can choose the most suitable phase shift. (C) 2016 Optical Society of America

Numerical simulations on inter-page crosstalk characteristics in three-dimensional shift multiplexed self-referential holographic data storage
Taisuke Eto, Masanori Takabayashi, Atsushi Okamoto, Masatoshi Bunsen, Takashi Okamoto
JAPANESE JOURNAL OF APPLIED PHYSICS, 55, 8, 08RD01.1, 08RD01.7, IOP PUBLISHING LTD, Aug. 2016, [Peer-reviewed]
English, Scientific journal, A three-dimensional (3D) shift multiplexing technique is applied to increase the number of multiplexed datapages in self-referential holographic data storage (SR-HDS), enabling holographic recording with purely one-beam geometry. In the 3D shift multiplexing technique, the recording medium is shifted not only along the x-and y-axes but also along the z-axis to multiplex the datapages. Because the shift directions in the 3D shift multiplexing technique are expanded compared with the conventional 2D technique, the number of multiplexed datapages is expected to be increased. We numerically clarify the appropriate 3D recording layout of holograms in which the effect of the inter-page crosstalk can be reduced after showing that datapages are multiplexed on shifting the recording medium along the z-axis. The results show 3D shift multiplexing can effectively realize high-density SR-HDS when appropriately designed layouts are used. (C) 2016 The Japan Society of Applied Physics.

Digital confocal microscopy using a virtual 4f-system based on numerical beam propagation for depth measurement without mechanical scanning
Yuta Goto, Atsushi Okamoto, Masataka Toda, Yasuyuki Kuno, Jin Nozawa, Kazuhisa Ogawa, Akihisa Tomita
JAPANESE JOURNAL OF APPLIED PHYSICS, 55, 8, 08RE04.1, 08RE04.6, IOP PUBLISHING LTD, Aug. 2016, [Peer-reviewed]
English, Scientific journal, We propose a digital confocal microscope using a virtual 4f-system based on numerical beam propagation for depth measurement without mechanical scanning. In our technique, the information in the sample target along the depth direction is obtained by defocusing the virtual 4f-system, which consists of two virtual lenses arranged in a computer simulation. The principle of our technique is completely different from that of the mechanical scanning method used in the conventional confocal microscope based on digital holography. By using the virtual 4f-system, the measurement and exposure time can be markedly reduced because multilayered tomographic images are generated using a single measurement. In this study, we tested the virtual depth imaging technique by measuring cover glasses arranged along the depth direction. (C) 2016 The Japan Society of Applied Physics

Entanglement generation by communication using phase-squeezed light with photon loss
Fumiaki Matsuoka, Akihisa Tomita, Atsushi Okamoto
PHYSICAL REVIEW A, 93, 3, 032308, AMER PHYSICAL SOC, Mar. 2016, [Peer-reviewed]
English, Scientific journal, To implement fault-tolerant quantum computation, entanglement generation with low error probability and high success probability is required. In a previous paper, we proposed the use of squeezed coherent light as a probe to generate entanglement between two atoms by communication and showed that the error probability is reduced well below the threshold of fault-tolerant quantum computation [F. Matsuoka et al., Phys. Rev. A 88, 022313 (2013)]. In this paper, we investigate the effect of photon loss mainly due to finite coupling efficiency to the cavity. The error probability with photon loss is calculated using a beam-splitter model for homodyne measurement of probe light. We examine the optimum conditions of the amplitude of the probe light and the degree of squeezing to minimize the error probability. We show that the phase -squeezed probe light yields lower error probability than a coherent -light probe, even with photon losses. A fault-tolerant quantum computation algorithm can be implemented under 87% transmittance by concatenating a seven-qubit error correction code for the phase-flip error.

Virtual interferogram-generation algorithm for phase measurement using two interferograms
Jin Nozawa, Atsushi Okamoto, Masataka Toda, Yasuyuki Kuno, Akihisa Tomita
PRACTICAL HOLOGRAPHY XXX: MATERIALS AND APPLICATIONS, 9771, SPIE-INT SOC OPTICAL ENGINEERING, 2016, [Peer-reviewed]
English, International conference proceedings, Phase-shifting digital holography is a technique for phase measurement with high spatial resolution and applied to many fields. This technique typically requires four phase-shifted interferograms between a signal beam and a reference beam. We focused on the two-step phase shifting algorithm, which needs only two phase-shifted interferograms and an intensity distribution of the reference beam to reduce the number of required interferograms. However, in this algorithm, the intensity of the reference beam must be much greater than that of the signal beam because this algorithm uses the quadratic formula and the inside of square root must be positive. This leads to the saturation of the dynamic range of the image sensor and the degradation of accuracy. In this paper, we propose a virtual interferogram-generation algorithm (VIGA) to improve the performance of phase-shifting digital holography only using two interferograms. This algorithm virtually generates a pi phase-shifted interferogram by the intensity distribution of the signal beam and that of the reference beam with an observed interferogram. Therefore, capturing two real interferograms and generating two virtual interferograms, the four-step phase shifting algorithm can be used for this method. Comparing to the conventional algorithm, the VIGA has no limitation in terms of the magnitude of the intensity. This means that the intensity of the reference beam and that of the signal beam can be equalized and the dynamic range saturation of the image sensors can be prevented. Therefore, the VIGA makes highly accurate phase measurement possible owing to the effective utilization of the dynamic range of the image sensors.

Highly accurate spatial mode generation using spatial cross modulation method for mode division multiplexing
Hiroki Sakuma, Atsushi Okamoto, Atsushi Shibukawa, Yuta Goto, Akihisa Tomita
NEXT-GENERATION OPTICAL COMMUNICATION: COMPONENTS, SUB-SYSTEMS, AND SYSTEMS V, 9774, SPIE-INT SOC OPTICAL ENGINEERING, 2016, [Peer-reviewed]
English, International conference proceedings, We propose a spatial mode generation technology using spatial cross modulation (SCM) for mode division multiplexing (MDM). The most well-known method for generating arbitrary complex amplitude fields is to display an off-axis computer-generated hologram (CGH) on a spatial light modulator (SLM). However, in this method, a desired complex amplitude field is obtained with first order diffraction light. This critically lowers the light utilization efficiency. On the other hand, in the SCM, the desired complex field is provided with zeroth order diffraction light. For this reason, our technology can generate spatial modes with large light utilization efficiency in addition to high accuracy. In this study, first, a numerical simulation was performed to verify that the SCM is applicable for spatial mode generation. Next, we made a comparison from two view points of the coupling efficiency and the light utilization between our technology and the technology using an off-axis amplitude hologram as a representative complex amplitude generation method. The simulation results showed that our technology can achieve considerably high light utilization efficiency while maintaining the enough coupling efficiency comparable to the technology using an off-axis amplitude hologram. Finally, we performed an experiment on spatial modes generation using the SCM. Experimental results showed that our technology has the great potential to realize the spatial mode generation with high accuracy.

Spatial-Mode Conversion using Random Diffuser and Spatial Light Modulator for Reduction of Modal Crosstalk
Koki Ishii, Atsushi Okamoto, Takehiro Tsuritani, Yuta Wakayama, Yuta Goto, Akihisa Tomita
NEXT-GENERATION OPTICAL COMMUNICATION: COMPONENTS, SUB-SYSTEMS, AND SYSTEMS V, 9774, SPIE-INT SOC OPTICAL ENGINEERING, 2016, [Peer-reviewed]
English, International conference proceedings, The mode-division multiplexing (MDM) technique enables the transmission of multiple signals within a multi-mode fiber (MMF) or a few-mode fiber (FMF). To construct an efficient and flexible MDM network in the same way as a wavelength-division multiplexing network, a mode conversion method with low modal crosstalk is required for switching between arbitrary spatial modes. However, in general, modal crosstalk is strongly dependent on the intensity pattern before mode conversion, and it is increased particularly for higher order modes. In order to reduce modal crosstalk, we propose a method using a random diffuser and a spatial light modulator (SLM). In the proposed method, firstly, the input spatial mode is dispersed uniformly by the random diffuser. Subsequently, the diffused phase distribution is canceled and converted into the desired spatial mode by the SLM, which displays phase difference between desired and diffused modes. Consequently, every spatial mode can be evenly converted into a desired mode. Here, we numerically simulate and confirm that the proposed method can reduce modal crosstalk compared to the conversion method without the random diffuser.

Two-channel algorithm for single-shot, high-resolution measurement of optical wavefronts using two image sensors
Jin Nozawa, Atsushi Okamoto, Atsushi Shibukawa, Masanori Takabayashi, Akihisa Tomita
APPLIED OPTICS, 54, 29, 8644, 8652, OPTICAL SOC AMER, Oct. 2015, [Peer-reviewed]
English, Scientific journal, We propose a two-channel holographic diversity interferometer (2ch-HDI) system for single-shot and highly accurate measurements of complex amplitude fields with a simple optical setup. In this method, two phase-shifted interference patterns are generated, without requiring a phase-shifting device, by entering a circularly polarized reference beam into a polarizing beam splitter, and the resulting patterns are captured simultaneously using two image sensors. However, differences in the intensity distributions of the two image sensors may lead to serious measurement errors. Thus, we also develop a two-channel algorithm optimized for the 2ch-HDI to compensate for these differences. Simulation results show that this algorithm can compensate for such differences in the intensity distributions in the two image sensors. Experimental results confirm that the combination of the 2ch-HDI and the calculation algorithm significantly enhances measurement accuracy. (c) 2015 Optical Society of America

Recording procedures for high-quality signal readout in self-referential holographic data storage
Masanori Takabayashi, Atsushi Okamoto, Taisuke Eto, Takashi Okamoto
APPLIED OPTICS, 54, 16, 5167, 5174, OPTICAL SOC AMER, Jun. 2015, [Peer-reviewed]
English, Scientific journal, Two methods are proposed to improve the readout quality of signals in self-referential holographic data storage (SR-HDS), in which no reference beam is required to record and read digital data holographically: the off-the-focus (OtF) method and the oversampling additional pattern (OsAP) method. The focal point is located outside of the recording medium in the OtF method, and the signal pattern is recorded with an additional pattern that possesses a higher spatial frequency than the signal pattern in the OsAP method. Experimental results show that both methods are effective for drastically improving the signal-to-noise ratio (SNR). In addition, through numerical simulation, it can be observed that the readout quality is improved by the achievement of homogeneous hologram distribution. (C) 2015 Optical Society of America

Optical tomography using a random diffuser and digital phase conjugation
Yuta Goto, Atsushi Okamoto, Atsushi Shibukawa, Akihisa Tomita, Kunihiro Sato
Progress in Biomedical Optics and Imaging - Proceedings of SPIE, 9319, SPIE, 2015, [Peer-reviewed]
English, International conference proceedings, We proposed a new technology for tomographic imaging based on beam diffusion and wavefront reconstruction through digital phase conjugation (DPC). The principle of this technology is highly unique and completely different from that of well-known optical coherence tomography (OCT) because it does not utilize the coherence property of light. In our experiment, it was shown that the depth resolution of smaller than 51/4m is obtained when using the objective lens with NA of 0.42. In addition, we achieved the extraction of the information from a specific specimen among several specimens arranged along optical axis.

VIRTUAL INTERFEROGRAM-GENERATION ALGORITHM FOR PHASE-SHIFTING DIGITAL HOLOGRAPHY
Jin Nozawa, Atsushi Okamoto, Masataka Toda, Yasuyuki Kuno, Akihisa Tomita
2015 20TH MICROOPTICS CONFERENCE (MOC), IEEE, 2015, [Peer-reviewed]
English, International conference proceedings, A virtual interferogram-generation algorithm is proposed to improve the performance of phase-shifting digital holography. Combining the intensity distribution of a signal and that of a reference beam with two observed interferograms, this algorithm generates four interferograms with different phases. Simulation results confirmed the basic operation of this algorithm.

OPTIMIZATION OF DIFFRACTION EFFICIENCY AND COUPLING EFFICIENCY IN SPATIAL MODE CONVERSION FOR PHOTONIC CROSS CONNECTER
Yanfeng Zhao, Atsushi Okamoto, Tomokazu Oda, Akihisa Tomita, Masatoshi Bunsen, Satoshi Honma
2015 20TH MICROOPTICS CONFERENCE (MOC), IEEE, 2015, [Peer-reviewed]
English, International conference proceedings, A photonic cross-connecter (PXC), which is capable of dynamic parallel conversions between different spatial modes, has been proposed. In this numerical simulation, to explore the potential of PXC, we investigated the optimal parameter settings at the hologram recording by implementing conversion from LP11 mode to LP21 mode.

HIGH-RESOLUTION AND SIMULTANEOUS MEASUREMENT ALONG THE DEPTH DIRECTION USING VIRTUAL PHASE CONJUGATION FOR OPTICAL TOMOGRAPHY
Yuta Goto, Atsushi Okamoto, Atsushi Shibukawa, Akihisa Tomita, Masanori Takabayashi
2015 20TH MICROOPTICS CONFERENCE (MOC), IEEE, 2015, [Peer-reviewed]
English, International conference proceedings, To improve the measurement speed of optical tomography based on the virtual phase conjugation, a virtual measurement position control technique is proposed. Tomographic images were observed with high depth-resolution and high acquisition rate in the numerical simulations.

Parallel and Simultaneous Spatial Mode Conversion using Photorefractive Crystal for Photonic Cross-Connect
Yanfeng Zhao, Atsushi Okamoto, Tomohiro Maeda, Yuki Hirasaki, Akihisa Tomita, Masatoshi Bunsen
NEXT-GENERATION OPTICAL COMMUNICATION: COMPONENTS, SUB-SYSTEMS, AND SYSTEMS IV, 9389, SPIE-INT SOC OPTICAL ENGINEERING, 2015, [Peer-reviewed]
English, International conference proceedings, In this paper, we present a novel technology for photonic cross-connect (PXC) in spatial mode domain for the realization of advanced and flexible optical transmission of spatial modes. The PXC is a kind of all -optical devices to switch highspeed optical signals for mode-division multiplexing (MDM) network and it is able to perform signal labeling in the spatial mode domain similar to current photonic switching in the wavelength domain. In addition, parallel and simultaneous mode conversion can be realized using multiplex holograms in a photorefractive crystal (PRC). In our experiment, during the recording process, a rewritable hologram is recorded in the PRC (LiNbO3) through the interference between the signal beam with certain input mode and the reference beam with the phase distribution of the desired output mode. Signal beams are generated by computer generated hologram (CGH) using a spatial light modulator (SLM) instead of an optical fiber emergent beam, and reference beams are generated by phase only modulation using another SLM. Subsequently, during the converting process, the input signal beam is converted into the desired output mode through the holographic diffract ion in the crystal and free-space propagation by an optical lens. By using phase code multiplexing method, parallel mode conversions can be realized. We performed an experiment on parallel mode conversions of several different conversion pairs. Signal beams and reference beams intersected in the PRC with an angle of 18.43 degree. The intensity distributions of converted modes were observed by CCD camera set on the Fourier plane. We confirmed that the two modes inter-conversion of LP11 with LP21 was successfully implemented.

Optical tomography using a random diffuser and digital phase conjugation
Yuta Goto, Atsushi Okamoto, Atsushi Shibukawa, Akihisa Tomita, Kunihiro Sato
OPTICAL TOMOGRAPHY AND SPECTROSCOPY OF TISSUE XI, 9319, SPIE-INT SOC OPTICAL ENGINEERING, 2015, [Peer-reviewed]
English, International conference proceedings, We proposed a new technology for tomographic imaging based on beam diffusion and wavefront reconstruction through digital phase conjugation (DPC). The principle of this technology is highly unique and completely different from that of well-known optical coherence tomography (OCT) because it does not utilize the coherence property of light. In our experiment, it was shown that the depth resolution of smaller than 5 mu m is obtained when using the objective lens with NA of 0.42. In addition, we achieved the extraction of the information from a specific specimen among several specimens arranged along optical axis.

IMPROVEMENT OF MEASUREMENT-SPEED BY VIRTUAL OPTICAL-SYSTEM FOR CONFOCAL LASER SCANNING MICROSCOPE
Yuta Goto, Atsushi Okamoto, Masataka Toda, Yasuyuki Kuno, Akihisa Tomita
2015 20TH MICROOPTICS CONFERENCE (MOC), IEEE, 2015, [Peer-reviewed]
English, International conference proceedings, We propose a virtual optical-system for the confocal laser scanning microscope, which enables to measure tomographic images with the high acquisition rate. In our technique, by utilizing the virtual optical-system based on complex-amplitude detection, multi-layered tomographic images can be measure collectively without mechanical scanning.

EXPANSION METHOD FOR DEPTH MEASUREMENT RANGE BASED ON NUMBER THEORY USING TWO WAVELENGTH LIGHT SOURCES
Jin Nozawa, Atsushi Okamoto, Masataka Toda, Yasuyuki Kuno, Akihisa Tomita
2015 20TH MICROOPTICS CONFERENCE (MOC), IEEE, 2015, [Peer-reviewed]
English, International conference proceedings, The expansion method for the depth measurement range is proposed. After capturing two wavelength phase images, the depth information is reconstructed by estimating the number of phase discontinuity in these images. The measurable depth-range can be expanded to hundreds times of wavelength.

Experiment on three-dimensional display using spatial cross modulation method
Yuta Kan, Atsushi Okamoto, Akihisa Tomita, Atsushi Shibukawa, Hisatoshi Funakoshi
PRACTICAL HOLOGRAPHY XXIX: MATERIALS AND APPLICATIONS, 9386, SPIE-INT SOC OPTICAL ENGINEERING, 2015, [Peer-reviewed]
English, International conference proceedings, We performed an experiment on a 3D display by employing spatial cross modulation ( SCM) using a random diffuser and phase-only spatial light modulator (SLM). In our experiment, a 3D object, which is constructed using four 2D images acquired from different spatial positions, is generated and the encoded 3D object is then displayed on the SLM. The different object images are observed when the image sensor is moved to different spatial positions. The experimental results revealed that the SCM method allows the generation of arbitrarily complex amplitude fields with high diffraction efficiency and with almost no speckle noise.

Numerical simulations on 3D shift multiplexed self-referential holographic data storage: shift multiplexing properties along z-axis
Taisuke Eto, Masanori Takabayashi, Atsushi Okamoto, Masatoshi Bunsen, Takashi Okamoto
2015 20TH MICROOPTICS CONFERENCE (MOC), IEEE, 2015, [Peer-reviewed]
English, International conference proceedings, The 3D shift multiplexing method for high-density self-referential holographic data storage is proposed. As the fundamental evaluations of the proposed method, we focus on the multiplexing properties along the z-axis. Concretely, we demonstrate the z-shift multiplexing of 25 datapages after clarifying the shift selectivity along the z-axis.

Evaluation of the phase randomness of a light source in quantum-key-distribution systems with an attenuated laser
Toshiya Kobayashi, Akihisa Tomita, Atsushi Okamoto
PHYSICAL REVIEW A, 90, 3, 032320, AMER PHYSICAL SOC, Sep. 2014, [Peer-reviewed]
English, Scientific journal, Phase-randomized light is one of the key assumptions in the security proof of the Bennett-Brassard 1984 (BB84) quantum-key-distribution (QKD) protocol using an attenuated laser. Though the assumption has been believed to be satisfied for conventional systems, it should be reexamined for current high-speed QKD systems. The phase correlation may be induced by the overlap of the optical pulses, the interval of which decreases as the clock frequency increases. The phase randomness was investigated experimentally by measuring the visibility of interference. An asymmetric Mach-Zehnder interferometer was used to observe the interference between adjacent pulses from a gain-switched distributed feedback laser diode driven at 10 GHz. Low visibility was observed when the minimum drive current was set far below the threshold, while interference emerged when the minimum drive current was close to the threshold. The theoretical evaluation on the impact of the imperfect phase randomization provides target values for the visibility to guarantee the phase randomness. The experimental and theoretical results show that secure implementation of decoy BB84 protocol is achievable even for the 10-GHz clock frequency by using the laser diode under proper operating conditions.

Shift-multiplexed self-referential holographic data storage
Masanori Takabayashi, Atsushi Okamoto, Taisuke Eto, Takashi Okamoto
APPLIED OPTICS, 53, 20, 4375, 4381, OPTICAL SOC AMER, Jul. 2014, [Peer-reviewed]
English, Scientific journal, The feasibility and the properties of shift-multiplexed self-referential holographic data storage (SR-HDS) were investigated. Although SR-HDS has attractive features as typified by referenceless holographic recording, its multiplexing properties, which are consummately important for holographic data storage, have not been clarified until now. The results of numerical and experimental evaluations of medium shift dependence in SR-HDS clarified that the shift selectivity is almost the same as in collinear holography. Furthermore, 25 datapages were successfully shift-multiplexed with the shift pitch of 8.3 m by the numerical simulation. (C) 2014 Optical Society of America

Background light reduction method with a double phase conjugate mirror and a phase plate for optical inter-satellite communications
Kaori Nishimaki, Atsushi Okamoto, Atsushi Shibukawa, Akihisa Tomita, Yoshihisa Takayama, Masatoshi Bunsen
JAPANESE JOURNAL OF APPLIED PHYSICS, 53, 8, IOP PUBLISHING LTD, Jul. 2014
English, Scientific journal, In optical intersatellite communication, the background light consisting mainly of sunlight decrease transmission rate with increasing bit error. A spatial filtering system using a double-phase-conjugate mirror (DPCM) and a phase plate is proposed to block the background light, which cannot be filtered out by using wavelength filters, polarization filters, or dousers. In this system, the effect of wavefront distortion caused by the phase plate and the compensation effect of the distortion by phase conjugate light from the DPCM are effectively combined for spatially separating signal light and background light. We demonstrated the reduction of the background light by the proposed system and optimized the phase plate for maximizing this reduction effect. As a result, it was clarified that the transmission rate can be drastically improved up to 11-fold. (C) 2014 The Japan Society of Applied Physics

Dynamically Reconfigurable Characteristics of a Double Phase Conjugate Mirror Using Sn2P2S6 Crystals and Their Application to Optical Inter-Satellite Communication
NISHIMAKI KAORI, OKAMOTO ATSUSHI, SHIBUKAWA ATSUSHI, TAKABAYASHI MASANORI, TOMITA AKIHISA, TAKAYAMA YOSHIHISA
Opt Rev, 21, 3, 415, 424, Jun. 2014, [Peer-reviewed]
English

Digital phase conjugate mirror by parallel arrangement of two phase-only spatial light modulators
Atsushi Shibukawa, Atsushi Okamoto, Yuta Goto, Satoshi Honma, Akihisa Tomita
OPTICS EXPRESS, 22, 10, 11918, 11929, OPTICAL SOC AMER, May 2014, [Peer-reviewed]
English, Scientific journal, In a conventional digital phase conjugation system, only the phase of an input light is time-reversed. This deteriorates phase conjugation fidelity and restricts application fields to specific cases only when the input light has uniformly-distributed scattered wavefront. To overcome these difficulties, we present a digital phase conjugate mirror based on parallel alignment of two phase-only spatial light modulators (SLMs), in which both amplitude and phase of the input light can be time-reversed. Experimental result showed that, in the phase conjugation through a holographic diffuser with diffusion angle of 0.5 degree, background noises decrease to 65% by our digital phase conjugation mirror. (C)2014 Optical Society of America

Spatial cross modulation method using a random diffuser and phase-only spatial light modulator for constructing arbitrary complex fields
Atsushi Shibukawa, Atsushi Okamoto, Masanori Takabayashi, Akihisa Tomita
OPTICS EXPRESS, 22, 4, 3968, 3982, OPTICAL SOC AMER, Feb. 2014, [Peer-reviewed]
English, Scientific journal, We propose a spatial cross modulation method using a random diffuser and a phase-only spatial light modulator (SLM), by which arbitrary complex-amplitude fields can be generated with higher spatial resolution and diffraction efficiency than off-axis and double-phase computer-generated holograms. Our method encodes the original complex object as a phase-only diffusion image by scattering the complex object using a random diffuser. In addition, all incoming light to the SLM is consumed for a single diffraction order, making a diffraction efficiency of more than 90% possible. This method can be applied for holographic data storage, three-dimensional displays, and other such applications. (C) 2014 Optical Society of America

Progressive phase conjugation and its application in reconfigurable spatial-mode extraction and conversion
Atsushi Okamoto, Tomohiro Maeda, Yuki Hirasaki, Akihisa Tomita, Kunihiro Sato
MICRO-OPTICS 2014, 9130, SPIE-INT SOC OPTICAL ENGINEERING, 2014, [Peer-reviewed]
English, International conference proceedings, We develop a new technology, which is referred to as progressive phase conjugation (PPC), in which phase conjugation is electrically performed without requiring a coherent reference beam by fusion using a reference-free spatial phase detection and spatial phase modulation. This method enables remote setting of a phase detector from the signal transmitter without an additional transmission line for the reference beam. It also enables realization of high-speed and dynamic wavefront compensation owing to its open-loop architecture using the single-shot phase detection method. Therefore, the PPC is applicable to a wide range of optical communication technologies, including the reconfigurable spatial-mode extraction and conversion of mode transmission in a multi-mode fiber (MMF). In our experiment, spatial modes are generated by directing a laser beam into a MMF with a 50-micron core diameter. At the output side of the optical fiber, the phase distributions of the spatial modes are detected using the reference-free phase detector constructed by combining a spatial filtering method with holographic diversity interferometry using two CCD imagers. Then, the phase conjugate distribution of the detected phase pattern is displayed on a LCOS-type SLM. We confirm that the PPC system can extract a specific mode pattern with a considerably low crosstalk of less than 1% by displaying the corresponding phase-conjugation pattern on the SLM. In addition, we demonstrated a reconfigurable spatial-mode conversion by the phase control technology using the SLM. By applying the spatial phase modulation to an optical beam incident on the SLM, the spatial mode of the output beam is flexibly changed.

High - speed bridge circuit for InGaAs avalanche photodiode single - photon detector
Hirofumi Hashimoto, Akihisa Tomita, Atsushi Okamoto
ADVANCES IN PHOTONICS OF QUANTUM COMPUTING, MEMORY, AND COMMUNICATION VII, 8997, SPIE-INT SOC OPTICAL ENGINEERING, 2014, [Peer-reviewed]
English, International conference proceedings, Because of low power consumption and small footprint, avalanche photodiodes (APD) have been commonly applied to photon detection. Recently, high speed quantum communication has been demonstrated for high bit-rate quantum key distribution. For the high speed quantum communication, photon detectors should operate at GHz-clock frequencies. We propose balanced detection circuits for GHz-clock operation of InGaAs-APD photon detectors. The balanced single photon detector operates with sinusoidal wave gating. The sinusoidal wave appearing in the output is removed by the subtraction from APD signal without sharp band-elimination filters. Omission of the sharp filters removes the constraint on the operating frequency of the single photon detector. We present two designs, one works with two identical APDs, the other with one APD and a low-pass filter. The sinusoidal gating enables to eliminate the gating noise even with the simple configuration of the latter design. We demonstrated the balanced single photon detector operating with 1.020GHz clock at 233 K, 193 K, and 186.5 K. The dark count probability was 4.0 x 10(-4) counts/pulse with the quantum efficiency of 10% at 233K, and 1.6 x 10(-4) counts/pulse at 186.5 K. These results were obtained with easily available APDs (NR8300FP-C. C, RENESASS) originally developed for optical time-domain reflectmeters.

Reconfigurable Spatial Mode Conversion using a Phase-Type Spatial Light Modulator
Tomohiro Maeda, Atsushi Okamoto, Yuki Hirasaki, Atsushi Shibukawa, Akihisa Tomita
2014 OPTOELECTRONICS AND COMMUNICATIONS CONFERENCE AND AUSTRALIAN CONFERENCE ON OPTICAL FIBRE TECHNOLOGY (OECC/ACOFT 2014), 517, 518, IEEE, 2014, [Peer-reviewed]
English, International conference proceedings, We propose the reconfigurable spatial mode conversion method using a phase-type spatial light modulator, and implement the experiment for interconversion among LP01, LP11, and higher-order spatial modes.

Adaptive Compensation for Extraction of Spatial Modes using Progressive Phase Conjugation
Yuki Hirasaki, Atsushi Okamoto, Tomohiro Maeda, Akihisa Tomita, Kunihiro Sato
2014 OPTOELECTRONICS AND COMMUNICATIONS CONFERENCE AND AUSTRALIAN CONFERENCE ON OPTICAL FIBRE TECHNOLOGY (OECC/ACOFT 2014), 230, +, IEEE, 2014, [Peer-reviewed]
English, International conference proceedings, We experimentally perform the adaptive compensation of distorted spatial modes after passing through a multi-mode fiber and the simultaneous extraction of multiple spatial modes by using progressive phase conjugation.

Evaluation of the phase correlation between the optical pulses for transmission in quantum key distribution
Toshiya Kobayashi, Akihisa Tomita, Atsushi Okamoto
ADVANCES IN PHOTONICS OF QUANTUM COMPUTING, MEMORY, AND COMMUNICATION VII, 8997, SPIE-INT SOC OPTICAL ENGINEERING, 2014, [Peer-reviewed]
English, International conference proceedings, One of the key assumptions in the security proof of BB84 quantum key distribution (QKD) protocol with a weak coherent light source is that the phase of each pulse emitted from the source is random. If the phases correlated, an efficient eavesdropping method exists, and more sacrifice bits are necessary to guarantee the security of the protocol. The phase correlation between the adjacent pulses was examined experimentally, for the first time, by measuring the visibility of interference. An asymmetric Mach-Zehnder interferometer was used to observe the interference between adjacent pulses from a distributed feedback (DFB) laser diode driven by 10 GHz clock signal. Clear interference was observed when the DC bias current exceeds the laser threshold. This high visibility implies phase correlation between pulses. In contrast, only a low visibility, i.e. very weak phase correlation, was observed when the DC bias current was set far below the threshold. The phase correlation became stronger as the DC bias current increased. The experimental results imply that a QKD equipment implementing BB84 protocol with a coherent light source is secure as long as the laser is operated in gain-switch even for 10 GHz clock frequency.

Effectiveness of double phase conjugate mirror for optical inter-satellite communication with large shift tolerance
Kaori Nishimaki, Atsushi Okamoto, Akihisa Tomita, Yoshihisa Takayama, Masatoshi Bunsen
Technical Digest of the 18th Microoptics Conference, MOC 2013, 01 Dec. 2013
We propose an innovative optical inter-satellite communication system with a double phase conjugate mirror. The proposed system improves the acquisition, tracking and background light reduction functions by utilization of phase conjugation. This paper reports on the temporal and spatial characteristics of double phase conjugate mirror to consider large shift tolerance. © 2013 The Japan Society of Applied Physics.

Double-Referential Holography and Spatial Quadrature Amplitude Modulation
Keisuke Zukeran, Atsushi Okamoto, Masanori Takabayashi, Atsushi Shibukawa, Kunihiro Sato, Akihisa Tomita
JAPANESE JOURNAL OF APPLIED PHYSICS, 52, 9, 09LD13.1-09LD13.9, IOP PUBLISHING LTD, Sep. 2013, [Peer-reviewed]
English, Scientific journal, We proposed a double-referential holography (DRH) that allows phase-detection without external additional beams. In the DRH, phantom beams, prepared in the same optical path as signal beams and preliminary multiplexed in a recording medium along with the signal, are used to produce interference fringes on an imager for converting a phase into an intensity distribution. The DRH enables stable and high-accuracy phase detection independent of the fluctuations and vibrations of the optical system owing to medium shift and temperature variation. Besides, the collinear arrangement of the signal and phantom beams leads to the compactness of the optical data storage system. We conducted an experiment using binary phase modulation signals for verifying the DRH operation. In addition, 38-level spatial quadrature amplitude modulation signals were successfully reproduced with the DRH by numerical simulation. Furthermore, we verified that the distributed phase-shifting method moderates the dynamic range consumption for the exposure of phantom beams. (c) 2013 The Japan Society of Applied Physics

Method of Phase and Amplitude Modulation/Demodulation Using Datapages with Embedded Phase-Shift for Holographic Data Storage
Masatoshi Bunsen, Shuhei Umetsu, Masanori Takabayashi, Atsushi Okamoto
JAPANESE JOURNAL OF APPLIED PHYSICS, 52, 9, 09LD04.1-09LD04.5, IOP PUBLISHING LTD, Sep. 2013, [Peer-reviewed]
English, Scientific journal, A technique for the phase and amplitude detection of object beams with multivalued phase and amplitude modulation is proposed for holographic storage systems. Generally, the spatial distribution of the complex amplitude of the object beam can be precisely detected by phase-shifting interferometric measurements in which the phase of the reference wave for interferometry is temporally or spatially changed in the datapage retrieval process. On the other hand, our technique allows fast, accurate, and feasible phase and amplitude demodulations by preliminary embedding phase shift into the phase signal of the datapage during recording. This technique will significantly improve the data transfer rate and vibration tolerance of the holographic storage system because the complex amplitudes of the object beam carrying datapages can be detected by single-shot image capturing. The optical system for datapage replay will also be simplified because there is no need to use any phase-shifting device during data retrieval. The single-shot detection of the phase-modulated datapage is experimentally demonstrated. (c) 2013 The Japan Society of Applied Physics

Digital Image Diffusion Technique for Suppressing Interpage Crosstalk in Holographic Data Storage
Atsushi Shibukawa, Atsushi Okamoto, Yuta Wakayama, Akihisa Tomita, Hisatoshi Funakoshi, Kunihiro Sato
JAPANESE JOURNAL OF APPLIED PHYSICS, 52, 9, 09LD03.1-09LD03.9, IOP PUBLISHING LTD, Sep. 2013, [Peer-reviewed]
English, Scientific journal, To suppress interpage crosstalk that strongly restricts holographic data storage capacity, a digital image diffusion technique was proposed. In this technique, signal and crosstalk components are separated from the propagation angle difference produced by using a random diffuser and the nature of phase conjugate lights. The most attractive feature of the technique is that crosstalk suppression can be conducted while mostly keeping the conventional holographic data storage system unchanged by integrating optical processing and digital processing effectively. The connection between the two types of processing is realized by using two spatial light modulators for complex amplitude generation and phase detection methods for complex amplitude measurement. The simulation results showed that the proposed technique could increase the recording density 5.5-fold and reduce the shift pitch by a factor of 5 in comparison with conventional multiplexing methods when the diffusion angle of the diffuser is 10 degrees. (c) 2013 The Japan Society of Applied Physics

Entanglement generation by communication using squeezed states
Fumiaki Matsuoka, Akihisa Tomita, Atsushi Okamoto
Physical Review A - Atomic, Molecular, and Optical Physics, 88, 2, 022313.1-022313.7, 12 Aug. 2013, [Peer-reviewed]
English, Scientific journal, In order to improve the error probability of generating entanglement by communication for quantum computation, we propose the use of squeezed light. When generating entanglement between two atoms by communication, the error probability can be reduced by increasing the distance between quantum states of probe light in phase space. The phase rotation of light depends on the atom-photon coupling strength and the light amplitude, which are limited in practice. A large error probability has been expected for coherent probe light. If we assume typical values of light amplitude and phase rotation, α=100 and θ=0.01, the error probability is estimated to be Pcoh(min)=0.14 and Pcoh(hom)=0.23 for minimum error discrimination and homodyne measurements. The error probability can be reduced to Psqu(min)=1.73×10-8 and Psqu(hom)=4.09×10-5 using squeezed coherent light, where the same values of the mean photon number and the phase rotation angle are assumed for the coherent light probe. These values satisfy the requirements for scalable quantum computation. © 2013 American Physical Society.

Mode demultiplexer using angularly multiplexed volume holograms
Yuta Wakayama, Atsushi Okamoto, Kento Kawabata, Akihisa Tomita, Kunihiro Sato
OPTICS EXPRESS, 21, 10, 12920, 12933, OPTICAL SOC AMER, May 2013, [Peer-reviewed]
English, Scientific journal, This study proposes a volume holographic demultiplexer (VHDM) for extracting the spatial modes excited in a multimode fiber. A unique feature of the demultiplexer is that it can separate a number of multiplexed modes output from a fiber in different directions by using multi-recorded holograms without beam splitters, which results in a simple configuration as compared with that using phase plates instead of holograms. In this study, an experiment is conducted to demonstrate the basic operations for three LP mode groups to confirm the performance of the proposed VHDM and to estimate the signal-to-crosstalk noise ratio (SNR). As a result, an SNR of greater than 20 dB is obtained. (C) 2013 Optical Society of America

Selective multimode excitation using volume holographic mode multiplexer
Kohei Aoki, Atsushi Okamoto, Yuta Wakayama, Akihisa Tomita, Satoshi Honma
Optics Letters, 38, 5, 769, 771, 01 Mar. 2013, [Peer-reviewed]
English, Scientific journal, We propose a mode multiplexer based on volume holograms to realize a simple and efficient mode-division-multiplexed transmission system that supports a large number of modes. Selective multiexcitation of three spatial modes into a conventional multimode fiber is experimentally demonstrated. This device could potentially multiplex 10 or more modes. Future perspectives of the mode multiplexer for application in mode-division multiplexing are also discussed. © 2013 Optical Society of America.

Self-referential holography and its applications to data storage and phase-to-intensity conversion
Masanori Takabayashi, Atsushi Okamoto
OPTICS EXPRESS, 21, 3, 3669, 3681, OPTICAL SOC AMER, Feb. 2013, [Peer-reviewed]
English, Scientific journal, Holographic recording methods require the use of a reference beam that is coherent with the signal beam carrying the information to be recorded. In this paper, we propose self-referential holography (SRH) for holographic recording without the use of a reference beam. SRH can realize purely one-beam holographic recording by considering the signal beam itself as the reference beam. The readout process in SRH is based on energy transfer by inter-pixel interference in holographic diffraction, which depends on the spatial phase difference between the recorded phase and the readout phase. The phase-modulated recorded signal is converted into an intensity-modulated beam that can be easily detected using a conventional image sensor. SRH can be used effectively for holographic data storage and phase-to-intensity conversion. (C) 2013 Optical Society of America

Separation of LP modes using volume holographic demultiplexer with a dual-wavelength method for mode division multiplexing
Kento Kawabata, Atsushi Okamoto, Satoshi Honma, Yuta Wakayama, Kunihiro Sato, Akihisa Tomita
NEXT-GENERATION OPTICAL COMMUNICATION: COMPONENTS, SUB-SYSTEMS, AND SYSTEMS II, 8647, 86470C.1-86470C.7, SPIE-INT SOC OPTICAL ENGINEERING, 2013
English, International conference proceedings, We propose a volume holographic mode demultiplexer incorporating a dual-wavelength method, which enables us to easily and flexibly set up the receiving system in mode division multiplexing for a large number of mode multiplexing. This demultiplexer can separate a lot of multiplexed modes with different wavelengths through angularly hologram multiplexing by appropriate angular difference between the two holographic writing beams. Thereby, the proposed method can be applicable to wavelength division multiplexing systems. In this study, we demonstrated the mode separation using the proposed demultiplexer with dual-wavelength. The results showed that the separation ratios of three LP modes reached around 90%.

Performance evaluation of holographic data storage system with phase-shift embedded SQAM datapages　　　　　　　　　　　　　　　
Shuhei Umetsu, Masatoshi Bunsen, Masanori Takabayashi, Atsushi Okamoto
Technical Digest of the 18th Microoptics Conference, MOC 2013, 2013
English, International conference proceedings, We quantitatively investigate the performance of holographic data storage system with Spatial Quadrature Amplitude Modulation datapages in which intensity and phase modulations are combined. The phase-shift required for phase demodulation is embedded in the datapage. Root Mean Square Error of demodulated phase value and Symbol Error Rate are experimentally evaluated. © 2013 The Japan Society of Applied Physics.

Conversion and extraction of spatial modes from a multimode fiber by reference-free holographic-diversity interferometry　　　　　　　　　　　　　　　
Yuki Hirasaki, Atsushi Okamoto, Tomohiro Maeda, Akihisa Tomita, Yuta Wakayama
2013 18th OptoElectronics and Communications Conference Held Jointly with 2013 International Conference on Photonics in Switching, OECC/PS 2013, 2013
English, International conference proceedings, The wave fronts of speckle fields exiting a multimode fiber are controlled by using a spatial light modulator in cooperation with reference-free holographic diversity interferometry for the high performance adaptive compensation and multiplex transmission. © 2013 IEICE.

Spatial mode excitation and separation using spatial phase control technology　　　　　　　　　　　　　　　
Atsushi Okamoto, Akihisa Tomita, Kento Kawabata, Yuta Wakayama
2013 18th OptoElectronics and Communications Conference Held Jointly with 2013 International Conference on Photonics in Switching, OECC/PS 2013, 2013
English, International conference proceedings, Computer-generated holography is actively used to generate the spatial mode distribution required for mode excitation and hologram writing. In addition, we propose a new transmission scheme using the phase conjugation technology. © 2013 IEICE.

Optimization of optical parameters for quantum information processing inside photonic crystals
Hiroyuki Nihei, Atsushi Okamoto
13th International Conference on Numerical Simulation of Optoelectronic Devices, NUSOD 2013, 59, 60, 2013, [Peer-reviewed]
English, International conference proceedings, We have optimized the control laser strength to carry out quantum information processing inside photonic crystals, by calculating the time-averaged probabilities of finding an atom on excited states encoding the quantum information. © 2013 IEEE.

Holographic-diversity interferometry for reference-free phase detection
Tomohiro Maeda, Atsushi Okamoto, Akihisa Tomita, Yuki Hirasaki, Yuta Wakayama, Masatoshi Bunsen
Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest, 2013, [Peer-reviewed]
English, International conference proceedings, Reference-free phase detection is demonstrated using advanced holographic diversity interferometry in which a virtual light source is locally produced from an object light passed through testing samples to simultaneously generate two phase-shifted interferograms. © 2013 IEEE.

Confined light composed of a single localized mode inside photonic crystals for a qubit
Hiroyuki Nihei, Atsushi Okamoto
OPTICAL AND QUANTUM ELECTRONICS, 44, 3-5, 265, 271, SPRINGER, Jun. 2012, [Peer-reviewed]
English, Scientific journal, We have demonstrated that light is confined in a single mode near a very small defect (such as an impurity atom) embedded in photonic crystals by coherent control using a dark line that is a spectrum singularity leading to the complete quenching of emission. In this demonstration, we have clarified the strong confinement and a very short response time, as compared with the widely used tunable PBG method. These features are useful for keeping the memory in a two-state quantum system such as a quantum bit (qubit) and for processing quantum information.

Multiple Recording and Reconstruction of Spatial Modes using Volume Holographic Mode Multiplexer for Mode-Division Multiplexing
AOKI KOHEI, OKAMOTO ATSUSHI, ODA TAKUYA, WAKAYAMA YUTA, TOMITA AKIHISA
Tech Dig Int Conf Opt photonics Des Fabr, 8th, 41, 42, 2012, [Peer-reviewed]
English

Optical design of a qubit embedded in photonic crystals for rotation gate operations
Hiroyuki Nihei, Atsushi Okamoto
2012 12TH INTERNATIONAL CONFERENCE ON NUMERICAL SIMULATION OF OPTOELECTRONIC DEVICES (NUSOD), 91, +, IEEE COMPUTER SOC, 2012, [Peer-reviewed]
English, International conference proceedings, We have optimized the optical design parameters of a qubit composed of excited states of an atom embedded in photonic crystals for operating rotation gates, using the coherent control of spontaneous emission from the atom.

Tunable Holographic Wavelength Filter Using a Photorefractive Polymer for Ultra-Broad Reconfigurable Add-Drop Multiplexers
Yuta Wakayama, Atsushi Okamoto, Akihisa Tomita
2012 International Conference on Photonics in Switching (PS), IEEE, 2012, [Peer-reviewed]
English, International conference proceedings, Experimental result shows a broad 175-nm tuning range in a photorefractive polymer-based holographic filter for reconfigurable optical add-drop multiplexing. The tuning range of the filter can further be enhanced to 770 nm.

Symbol Error Characteristics of Hybrid-Modulated Holographic Data Storage by Intensity and Multi Phase Modulation
Masanori Takabayashi, Atsushi Okamoto, Akihisa Tomita, Masatoshi Bunsen
JAPANESE JOURNAL OF APPLIED PHYSICS, 50, 9, 09ME05.1-09ME05.5, JAPAN SOC APPLIED PHYSICS, Sep. 2011, [Peer-reviewed]
English, Scientific journal, For the purpose of increasing the data density of holographic memories, we propose a novel signal modulation method named hybrid modulation method, which is a combination of multi level phase-modulated signals and intensity-modulated signals. As a first step, we show that the data density of holographic data storage is mainly determined by multiplexing numbers and by coding efficiency in input signals. In this study, we focus on increasing coding efficiency using the hybrid modulation method. From the results of recording and reading simulations based on the fast-Fourier transform beam propagation method, the hybrid modulation method achieves approximately 2 times higher data density than the conventional methods of two-level phase-only modulation and two-level intensity-only modulation. (C) 2011 The Japan Society of Applied Physics

Multilayer Collinear Holographic Memory with Movable Random Phase Mask
Atsushi Shibukawa, Atsushi Okamoto, Akihisa Tomita, Masanori Takabayashi, Kunihiro Sato
JAPANESE JOURNAL OF APPLIED PHYSICS, 50, 9, 09ME10.1-09ME10.5, JAPAN SOC APPLIED PHYSICS, Sep. 2011, [Peer-reviewed]
English, Scientific journal, We proposed a new multilayer collinear holographic memory (MCHM) with a movable random phase mask that can act as an interlayer crosstalk reducer. First, to clarify the feasibility of our proposed device, we showed that it has an extremely sharp shift selectivity along the thickness direction of medium of nearly 5.0 mu m when the numerical aperture of the objective lens is 0.60. Next, we demonstrated that the utilization of the movable random phase mask can suppress interlayer crosstalk sufficiently, resulting in the improvement in the quality of reconstructed signals. Moreover, we revealed that the MCHM, in which the parallel use of a multilayered technique and collinear shift multiplexing is performed, brings out the medium potential sufficiently in terms of signal to noise ratio and medium dynamic range consumption. Finally, we verified that the MCHM can achieve a nearly 2 times larger data density at least compared with a conventional collinear holographic memory. (C) 2011 The Japan Society of Applied Physics

Holographic diversity interferometry for optical storage
Atsushi Okamoto, Keisuke Kunori, Masanori Takabayashi, Akihisa Tomita, Kunihiro Sato
OPTICS EXPRESS, 19, 14, 13436, 13444, OPTICAL SOC AMER, Jul. 2011, [Peer-reviewed]
English, Scientific journal, This study proposes holographic diversity interferometry (HDI), a system that combines information from spatially dispersed plural image sensors to reconstruct complex amplitude distributions of light signals. HDI can be used to generate four holographic interference fringes having different phases, thus enabling optical phase detection in a single measurement. Unlike conventional phase-shifting digital holography, this system does not require piezoelectric elements and phase shift arrays. In order to confirm the effectiveness of HDI, we generated optical signals having multilevel phases and amplitudes by using two SLMs and performed an experiment for detection and demodulation with HDI. (C) 2011 Optical Society of America

Optical Inter-Satellite Communication with Dynamically Reconfigurable Optical Device Using Sn2P2S6 Crystal
Kaori Nishimaki, Atsushi Okamoto, Tomohiro Fujita, Alexander A. Grabar, Masanori Takabayashi, Jun Uozumi, Akihisa Tomita, Yoshihisa Takayama
FREE-SPACE LASER COMMUNICATION TECHNOLOGIES XXIII, 7923, 79230N, SPIE-INT SOC OPTICAL ENGINEERING, 2011
English, International conference proceedings, Since the optical inter-satellite communication has attractive advantages such as high-speed transmission with high confidence, almost no electronic magnetic interference, and low power consumption, it has been activity investigated. However, directivity control of the laser beams requires a bulky and complicated system in satellite mobile communications. A more flexible and high accurate system with small and simple mechanism has been desired. In this study, we propose a new method of optical inter-satellite communication with a dynamically reconfigurable optical directional device in which diffraction gratings are automatically rewritten and reorganized in response of incident conditions by moving satellites. For realizing such a device, we have developed Sn2P2S6 crystals which have a high sensitive photorefractivity and dynamic reconfigurable property. Furthermore, this crystal has hundreds times faster response than conventional photorefractive materials such as BaTiO3. These features are extremely advantageous to construct a high-speed and flexible communication system with a large tolerance to displacement of moving satellites. To investigate the possibility of the dynamically reconfigurable optical inter-satellite communication system, we experimentally evaluate the temporal and spatial characteristics of Sn2P2S6 crystals for the variation of the beam incident angle. Moreover, the diffraction beam from the crystal has phase conjugate wavefronts of the beam entering from the counter direction. We try to utilize this behavior to suppress the beam spread and to reduce the background light such as sunlight with a spatial filtering technique that has sensitivity in wavefront differences of the signal and background light. (241words)

All-optical demultiplexer based on dynamic multiple holograms for optical MIMO processing and mode division multiplexing
Takuya Oda, Atsushi Okamoto, Daiki Soma, Akihisa Tomita, Yuta Wakayama
BROADBAND ACCESS COMMUNICATION TECHNOLOGIES V, 7958, 79580J, SPIE-INT SOC OPTICAL ENGINEERING, 2011
English, International conference proceedings, We propose an all-optical demultiplexer based on dynamic multiple holograms using a photorefractive material for mode division multiplexing and optical MIMO processing systems. This demultiplexer can separate a specific spatial mode from multiplexed modes in a multi-mode fiber. In this study, we clarify a mode separation performance with various combinations of LP modes, and show the signal-to-noise ratio (SNR) can be improved by choosing appropriate mode combinations. In addition, to reveal the dependence of mode separation of the intensity ratio of the recording lights, we study the fluctuation of the SNR for LP0,1 mode by the combinations of multiplexed modes. Moreover, two additional recording techniques with a spatial light modulator (SLM) and phase conjugator are also proposed to improve the performance of the mode separation.

Ultra-wide tuning range of reconfigurable optical add-drop multiplexer using photorefractive polymer
Yuta Wakayama, Atsushi Okamoto, Akihisa Tomita, Kunihiro Sato
BROADBAND ACCESS COMMUNICATION TECHNOLOGIES V, 7958, 79580H, SPIE-INT SOC OPTICAL ENGINEERING, 2011
English, International conference proceedings, We propose a reconfigurable optical add-drop multiplexer with ultra-broadband tuning range over 770 nm using a photorefractive polymer. This add-drop multiplexer can optically switch the assignment of the waveband used for communications by only changing the incident angles of two beams writing a hologram. In this work, we clarified the condition in which the channel tuning can be carried out without the location change in the port array. We simulated on the add-drop operation, and showed the ultra-wide tuning range from 780 to 1550 nm. Moreover, we suggested an apodization method for the grating distribution by controlling the intensity ratio of the writing beams to enhance the diffraction efficiency in add-drop operation. As a result, we showed that the apodization method for the grating distribution can improve the diffraction efficiency.

Autonomous and dynamic reconfigurable waveguide for optical interconnection with large shift-tolerance
Atsushi Okamoto, Kazutaka Hira, Alexander A. Grabar, Hisatoshi Funakoshi, Yuta Wakayama, Akihisa Tomita
OPTOELECTRONIC INTERCONNECTS AND COMPONENT INTEGRATION XI, 7944, 79440G, SPIE-INT SOC OPTICAL ENGINEERING, 2011
English, International conference proceedings, In order to realize a dynamic reconfiguration technique that automatically switches configurations and functions of an optical device, we need a technique to control freely the connections of light inside and between devices without needing submicron-level alignments. In this study, we investigate the behavior of dynamic index gratings with nanoscale reversible self-organization in Sn2P2S6 crystals that we have newly developed so as to realize an autonomous and dynamic reconfigurable optical waveguide by externally controlling its motions with light and examine its basic properties. Experimental results showed autonomous and dynamic reconfigurations of the optical waveguide formed in a Sb doped Sn2P2S6 crystal with a 4 mm thickness for variations of an incident light position. We have successfully reconfigured the waveguide by a self-organization based on a photorefractive effect without cutting time series signals flowing through the waveguide, for variations of an incident light position long as approximately 2000 mu m. Furthermore, we have recognized tolerance up to around 0.2 degrees for incidence angles in the experiment. This technique allows us to connect light freely without needing spatial adjustments in a nanostructured optical waveguide seen in photonic crystal fibers. Moreover, it is a technique that can be applied to dynamic connections between optical fibers and integrated waveguides accompanied with time variations of spatial modes. We also verified a possibility of removable and replaceable optical connection by utilizing large shift-tolerance of the autonomous and dynamic reconfigurable waveguide.

All-optical demultiplexer based on dynamic multiple holograms for optical MIMO processing and mode division multiplexing
Takuya Oda, Atsushi Okamoto, Daiki Soma, Akihisa Tomita, Yuta Wakayama
BROADBAND ACCESS COMMUNICATION TECHNOLOGIES V, 7958, 79580J.1-79580J.9, SPIE-INT SOC OPTICAL ENGINEERING, 2011
English, International conference proceedings, We propose an all-optical demultiplexer based on dynamic multiple holograms using a photorefractive material for mode division multiplexing and optical MIMO processing systems. This demultiplexer can separate a specific spatial mode from multiplexed modes in a multi-mode fiber. In this study, we clarify a mode separation performance with various combinations of LP modes, and show the signal-to-noise ratio (SNR) can be improved by choosing appropriate mode combinations. In addition, to reveal the dependence of mode separation of the intensity ratio of the recording lights, we study the fluctuation of the SNR for LP0,1 mode by the combinations of multiplexed modes. Moreover, two additional recording techniques with a spatial light modulator (SLM) and phase conjugator are also proposed to improve the performance of the mode separation.

Optical Inter-Satellite Communication with Dynamically Reconfigurable Optical Device Using Sn2P2S6 Crystal
Kaori Nishimaki, Atsushi Okamoto, Tomohiro Fujita, Alexander A. Grabar, Masanori Takabayashi, Jun Uozumi, Akihisa Tomita, Yoshihisa Takayama
FREE-SPACE LASER COMMUNICATION TECHNOLOGIES XXIII, 7923, 79230N.1-79230N.9, SPIE-INT SOC OPTICAL ENGINEERING, 2011
English, International conference proceedings, Since the optical inter-satellite communication has attractive advantages such as high-speed transmission with high confidence, almost no electronic magnetic interference, and low power consumption, it has been activity investigated. However, directivity control of the laser beams requires a bulky and complicated system in satellite mobile communications. A more flexible and high accurate system with small and simple mechanism has been desired. In this study, we propose a new method of optical inter-satellite communication with a dynamically reconfigurable optical directional device in which diffraction gratings are automatically rewritten and reorganized in response of incident conditions by moving satellites. For realizing such a device, we have developed Sn2P2S6 crystals which have a high sensitive photorefractivity and dynamic reconfigurable property. Furthermore, this crystal has hundreds times faster response than conventional photorefractive materials such as BaTiO3. These features are extremely advantageous to construct a high-speed and flexible communication system with a large tolerance to displacement of moving satellites. To investigate the possibility of the dynamically reconfigurable optical inter-satellite communication system, we experimentally evaluate the temporal and spatial characteristics of Sn2P2S6 crystals for the variation of the beam incident angle. Moreover, the diffraction beam from the crystal has phase conjugate wavefronts of the beam entering from the counter direction. We try to utilize this behavior to suppress the beam spread and to reduce the background light such as sunlight with a spatial filtering technique that has sensitivity in wavefront differences of the signal and background light. (241words)

Ultra-wide tuning range of reconfigurable optical add-drop multiplexer using photorefractive polymer
Yuta Wakayama, Atsushi Okamoto, Akihisa Tomita, Kunihiro Sato
BROADBAND ACCESS COMMUNICATION TECHNOLOGIES V, 7958, 79580H.1-79580H.8, SPIE-INT SOC OPTICAL ENGINEERING, 2011
English, International conference proceedings, We propose a reconfigurable optical add-drop multiplexer with ultra-broadband tuning range over 770 nm using a photorefractive polymer. This add-drop multiplexer can optically switch the assignment of the waveband used for communications by only changing the incident angles of two beams writing a hologram. In this work, we clarified the condition in which the channel tuning can be carried out without the location change in the port array. We simulated on the add-drop operation, and showed the ultra-wide tuning range from 780 to 1550 nm. Moreover, we suggested an apodization method for the grating distribution by controlling the intensity ratio of the writing beams to enhance the diffraction efficiency in add-drop operation. As a result, we showed that the apodization method for the grating distribution can improve the diffraction efficiency.

多層化コリニアホログラムによる超高密度記録　　　　　　　　　　　　　　　
岡本 淳, 渋川敦史
光学, 40, 11, 591, 593, 2011, [Invited]

Optical interconnection between different spatial modes using double phase conjugate mirror with polarization alignment system
Yuta Wakayama, Atsushi Okamoto, Alexander A. Grabar, Kunihiro Sato
Optical Review, 18, 1, 117, 123, Jan. 2011, [Peer-reviewed]
English, Scientific journal, We propose a fundamental interconnection method using a polarization alignment system for waveguides having different spatial modes. In addition, as an example for the verification of the fundamental operation, we demonstrate an interconnection between a photonic crystal fiber and a laser that have obviously different spatial modes. The polarization alignment system operates synergistically with a self-written waveguide formed with a double phaseconjugate mirror. This technique enables us to interconnect a photonic crystal fiber with a laser source without complicated and time-consuming optical alignment. In this method, although it is not necessary to perform an external control for interconnection, the waveguide most suitable for connection is formed autonomously in a Sn2P2S6:Sb crystal developed for this purpose. There was a marked reduction in the polarization dependence of coupling efficiency, compared with that observed using a stand-alone double phase-conjugate mirror. © 2011 The Optical Society of Japan.

Double Phase Conjugate Mirror with Sb-Doped Sn2P2S6 Crystal for Different Incident Angles, Crystal Thickness, Total Incident Intensity and Polarization
Yuta Wakayama, Atsushi Okamoto, Alexander A. Grabar
FERROELECTRICS, 415, 1, 8, TAYLOR & FRANCIS LTD, 2011, [Peer-reviewed]
English, Scientific journal, We developed photorefractive Sb-doped Sn2P2S6 samples of different crystal thickness to investigate the properties of the media for double phase conjugation. The Sn2P2S6:Sb crystals have high coupling coefficient of 20 cm(-1), and show fast response time of 1.3 ms at total incident intensity of 0.3 W/cm(2). The maximum phase conjugate reflectivity of 32% was observed with a 4 mm thickness sample. To investigate the characteristics of Sn2P2S6:Sb for double phase conjugation, on the basis of the coupled wave equations, we showed the dependence of phase conjugate reflectivity on incident angle, crystal thickness, total incident intensity and polarization. From these results, the optimum incident condition was clarified for obtaining the highest phase conjugate reflectivity.

Enhancement of Repositioning Tolerance by Directionally Controlled Shift Selectivity of Speckle-Multiplexed Holograms
Masatoshi Bunsen, Seiji Fukuchi, Shuji Takahashi, Hirosuke Furuta, Atsushi Okamoto
JAPANESE JOURNAL OF APPLIED PHYSICS, 49, 8, 08KD06.1-08KD06.4, IOP PUBLISHING LTD, Aug. 2010, [Peer-reviewed]
English, Scientific journal, A method for directional control of shift selectivities of speckle-multiplexed holograms with a diffuser whose diffusion angle varies with the diffusion direction is proposed to enhance the tolerance of recorded holograms to repositioning error in holographic storage. The directional dependence and controllability of shift selectivities of holograms are experimentally investigated using various diffusers. By retrieving 50 speckle-multiplexed holograms with deliberate deviations from the original recording position and by measuring bit error rate, it is also confirmed that the tolerance to repositioning error is improved. (C) 2010 The Japan Society of Applied Physics

Polarization Alignment Free Interconnection by Dynamically Reconfigurable Double Phase Conjugation
WAKAYAMA YUTA, OKAMOTO ATSUSHI, GRABAR ALEXANDER A
Tech Dig Int Conf Opt photonics Des Fabr, 7th, 233, 234, 2010, [Peer-reviewed]
English

Mode division multiplex communication technique based on dynamic volume hologram and phase conjugation
Atsushi Okamoto, Kazuyuki Morita, Yuta Wakayama, Junya Tanaka, Kunihiro Sato
MICRO-OPTICS 2010, 7716, 771627.1-771627.10, SPIE-INT SOC OPTICAL ENGINEERING, 2010
English, International conference proceedings, We propose mode division multiplex communication technique that can split a specific spatial mode in light from a spatial mode multiplexed in an optical fiber by fusion of a phase conjugation technique with spatial filtering processing by multiplexed volume holograms and random diffusers. In mode division multiplexing, the optical signal outgoing from the multimode optical fiber is in a condition that optical information of plural spatial modes is overlapped, therefore it is difficult to de-multiplex electrically after light detection. Our technique enables to split it into each mode all optically and to compensate temporal modal shift dynamically. Mode de-multiplexing is realized by multiplexed holographic arithmetic device and phase matching of a wave surface for the spatial mode orthogonal to time. Therefore, if we use indices in conventional electronic processing, a very high-speed operation equivalent to that of 10-100PFLOPS can be realized without causing any delay in light information to be transmitted. Moreover, it can realize constructions of a system that can dynamically respond to temporal mode variations and distortions with fiber transmissions by using a photorefractive medium. Separating of around 60-70% was achieved in an experiment of separating three multiplexed spatial modes by controlling a volume type dynamic reconfigurable device based on LiNbO3. It was clarified that the separation performance improved by an appropriate random phase mask in the numerical analysis.

Development of Image-Based Simulation for Holographic Data Storage System by Fast Fourier Transform Beam-Propagation Method
Junya Tanaka, Atsushi Okamoto, Motoki Kitano
JAPANESE JOURNAL OF APPLIED PHYSICS, 48, 3, 03A028, 03A028-5, JAPAN SOCIETY APPLIED PHYSICS, Mar. 2009, [Peer-reviewed]
English, Scientific journal, We apply the fast Fourier transform beam-propagation method (FFT-BPM) to analyze holographic data storage systems (HDSSs), and develop an image-based simulation for diffraction characteristics in a transmission-type HDSS. The FFT-BPM is known as a very effective method for the design of large waveguides. By applying this method, we can obtain a beam profile in a recording medium that consists of a three-dimensional (3D) complex refractive-index distribution, and analyze the diffraction characteristics in page-oriented multiplexing holograms for an analytic region more practical than that required for the finite-difference time-domain (FDTD) method because of much lower computation time and memory. In this study, we demonstrate angular multiplexing by recording three data pages at different angles and visualize angular selectivity for diffraction efficiency and the sharpness of reconstructed images by a 3D numerical simulation. 2009 The Japan Society of Applied Physics DOI: 10.1143/JJAP.48.03A028

Time-domain differential detection of phase-modulated signals for phase-only holographic data storage
Masanori Takabayashi, Atsushi Okamoto, Kunihiro Sato
Japanese Journal of Applied Physics, 48, 3, 03A032, 03A032-5, INSTITUTE OF PURE AND APPLIED PHYSICS, Mar. 2009, [Peer-reviewed]
English, Scientific journal, Holographic data storage with phase-modulated signals has great advantages over conventional intensity-based memory. These include the efficient use of material dynamic range and light power in a spatial light modulator. On the other hand, phase-based holographic data storage has a disadvantage, which is the difficulty in distinguishing phase-modulated signals. We propose and demonstrate a new phasemodulated signal detection method with photorefractive two-wave mixing. This method has several advantages such as high energy efficiency, detection of multi valued phase-modulated signals, and alignment-free optics. In this study, we investigate the spatial resolution of the phase-modulated signal detection method and obtain a spatial resolution of 300-500 μm of incident pixels. © 2009 The Japan Society of Applied Physics.

Security Assessment of Two-Wave Encryption
Motoki Kitano, Atsushi Okamoto, Takayuki Sano
JAPANESE JOURNAL OF APPLIED PHYSICS, 48, 3, 03A036, 03A036-6, JAPAN SOCIETY APPLIED PHYSICS, Mar. 2009, [Peer-reviewed]
English, Scientific journal, To determine the degree of security in two-wave encryption under practical conditions, we present a novel numerical technique for simulating the recording and readout of two-wave encryption. The calculation results of the retrieval characteristics show that the diffraction efficiency in an incorrect decryption is 10 times as low as that in correct decryption key and that the output data with an incorrect key is a white noise image. We estimate the necessary key correlation to decrypt an encrypted data is 0.2 when the length of an encryption key is 2313. This means that the decoding probability of the encryption key in two-wave encryption is less than 10(-6) even if such a short key is used. (C) 2009 The Japan Society of Applied Physics DOI: 10.1143/JJAP.48.03A036

Experiments on Double Phase Conjugate Mirror with a Photorefractive Sb:Sn2P2S6 Crystal
Yasunori Kojima, Atsushi Okamoto, Alexander A. Grabar, Masanori Takabayashi, Kohei Shimayabu
FERROELECTRICS, 378, 121, 128, TAYLOR & FRANCIS LTD, 2009, [Peer-reviewed]
English, Scientific journal, We present various optical basic properties of a 1.5% doped Sb:Sn2P2S6 crystal experimentally and demonstrate a double phase conjugate mirror (DPCM). We measured the reflection, absorption and scattering of this crystal. The large coupling strength L = 8.2 was obtained by the experiment of two-wave mixing. In addition, we succeeded in the formation of the DPCM and achieved the high diffraction efficiency of 42%. This crystal was suitable for DPCM applications of high speed response.

Spatial resolutions for applying photorefractive polymers to diffractive elements
Atsushi Okamoto, Kazuhiro Harasaka, Masatoshi Bunsen, Masanori Takabayashi, Shuji Rokutanda
JOURNAL OF MODERN OPTICS, 56, 12, 1323, 1334, TAYLOR & FRANCIS LTD, 2009, [Peer-reviewed]
English, Scientific journal, Spatial resolutions of diffracted beams by photorefractive polymers are investigated in detail for applying the polymers to diffractive optical elements. The coupled wave equations for the four-wave mixing in photorefractive polymers and their solutions by applying the two-beam coupling approximation are derived taking the orientational enhancement effect into consideration. Characteristics of the diffraction efficiency of the polymers for the applied electric field, the incident angles of beams, the incident radiation intensity and the polarization are clarified. Furthermore, resolutions of diffracted images with the polymers are discussed by a numerical analysis from the viewpoint of the Bragg diffraction in a spatial frequency domain. An experiment with the TPD (tetra-phenyl-diphenyldiamine) acrylate based photorefractive polymers and the USAF test target is also performed to measure the spatial resolution of two-dimensional images diffracted by the polymer and to verify the calculated results. It is revealed that high resolution over 50 lp mm-1 can be obtained with sufficient diffraction efficiency in the case of the polymer thickness of several 10 mu m.

Nanophotonic Active Devices Using Tunability of Photonic Band Gaps
H. Nihei, A. Okamoto
FERROELECTRICS, 379, 225, 230, TAYLOR & FRANCIS LTD, 2009, [Peer-reviewed]
English, Scientific journal, We demonstrate a nanophotonic active device composed of a quantum dot embedded in photonic crystals with a tunable PBG provided using ferroelectric materials for fabricating photonic crystals. The quantum dot exhibits active-device operation including two switching operations: optical switching in a THz oscillator and optical switching in an optical memory. The significant feature of controllability provided using ferroelectric materials is that these two switching operations are combined, so that this controllability enables an active device to act as a multifunctional device that can operate as a THz oscillator and an optical memory.

All-optical tunable filter with photorefractive planar waveguide and suppression of crosstalk by apodized grating via photorefractive two-wave mixing
Satoshi Honma, Naoya Tsuda, Shinzo Muto, Kunihiro Sato, Atsushi Okamoto
OPTICAL DESIGN AND ENGINEERING III, PTS 1 AND 2, 7100, SPIE-INT SOC OPTICAL ENGINEERING, 2008, [Peer-reviewed]
English, International conference proceedings, The wavelength division multiplexing (WDM) technology effectively increases the bandwidth capacity of a communication line without installing additional fibers and increasing data bit rate to high levels. Optical add-drop modules are key components in WDM optical networks.
We propose two types of all-optical tunable filter with a photorefractive planar waveguide. The photo-induced index grating in the PR waveguide by control beams drops off a part of wavelength components in the WDM signal beam. It make possible to select the wavelength components of the signal beam by optically adjusting the wave vector of the grating. It is also possible to control bandwidth of the output signal by adjusting the broadening of the grating in the waveguide. The photorefractive effect is known as one of the most efficient nonlinear effects, and therefore the device is controllable by the relative low beam power comparing with the conventional devices using non-linear optical effects.
The channel crosstalk is generated by using uniformly broadened index grating. We note that the nonreciprocal energy transfer between the two control beams via a photorefractive two-wave mixing causes the nonuniform index grating like Gaussian profile. We therefore suggest the suppression method of channel crosstalk by adjusting the incident intensity of the control beams.

All-optical switch and tunable filter with photorefractive crystal
Satoshi Honma, Naoya Tsuda, Atsushi Okamoto, Shinzo Muto
2008 JOINT CONFERENCE OF THE OPTO-ELECTRONICS AND COMMUNICATIONS CONFERENCE AND THE AUSTRALIAN CONFERENCE ON OPTICAL FIBRE TECHNOLOGY, VOLS 1 AND 2, 570, +, IEEE, 2008, [Peer-reviewed]
English, International conference proceedings, We propose an optical switch and tunable filter with a photorefractive crystal. Theses devices are controllable by relatively low power beams. We analyze the diffraction efficiency and give the basic experimental result.

Recording schedule for partially coherent hologram multiplexing in a photorefractive medium.
Ito T, Okamoto A, Sato K
Applied optics, 46, 23, 5902, 5911, 23, Aug. 2007, [Peer-reviewed]

Recording schedule for partially coherent hologram multiplexing in a photorefractive medium
Terumasa Ito, Atsushi Okamoto, Kunihiro Sato
APPLIED OPTICS, 46, 23, 5902, 5911, OPTICAL SOC AMER, Aug. 2007, [Peer-reviewed]
English, Scientific journal, The exposure schedule for partially coherent hologram multiplexing, in which data pages are multiplexed by multiple signal beams and a single reference beam, is investigated in detail for the case of a pi/2 phase-shifted photorefractive medium. We found that the optimum recording schedule for partially coherent multiplexing cannot be determined by the classical recording schedule theory because of time-constant errors induced by partially coherent interaction between a reference beam and self-diffraction signal beams. To overcome the issue, we derive a modified recursion equation that accounts for the time-constant errors, and we also propose a novel iterative recording-schedule correction algorism for finding the optimum solution. In the calculation with hologram multiplicity of 30 and photorefractive coupling strength of 3.0, we could successfully obtain a flat diffraction-efficiency profile after the second recursion. (c) 2007 Optical Society of America.

Digital image multiplexing/demultiplexing method using spatial spectral diffusion and virtual phase conjugation technique for reduction of dynamic range consumption in holographic medium　　　　　　　　　　　　　　　
Yuta Goto, Atsushi Okamoto, Masanori Takabayashi, Kazuhisa Ogawa, Akihisa Tomita
Japanese Journal of Applied Physics, 56, 98, 09NA07-1, 09NA07-8, Aug. 2007, [Peer-reviewed]
English, Scientific journal

Nondestructive readout of a photorefractive hologram by phase-conjugate copying in a one-crystal configuration.
Ito T, Okamoto A, Funakoshi H, Sato K
Applied optics, 46, 13, 2443, 2452, 13, May 2007, [Peer-reviewed]

Nondestructive readout of a photorefractive hologram by phase-conjugate copying in a one-crystal configuration
Terumasa Ito, Atsushi Okamoto, Hisatoshi Funakoshi, Kunihiro Sato
APPLIED OPTICS, 46, 13, 2443, 2452, OPTICAL SOC AMER, May 2007, [Peer-reviewed]
English, Scientific journal, We propose a novel phase-conjugate copying method for nondestructive readout of a volatile photore-fractive hologram. In the one-crystal configuration, two holographic memories and a mutually pumped phase conjugator (MPPC) are formed within a single photorefractive crystal, instead of using multiple crystals. Two memories share the same hologram and complement each other in refreshing the hologram. A MPPC suppresses fanning noise and automatically aligns the wavefront of the reference and readout beams. We found the optimum configuration to achieve nondestructive readout from calculations and geometric consideration. In the experiments with a BaTiO3 crystal, a continuous readout of 20 times longer than the recording time was achieved. (c) 2007 Optical Society of America.

Coherent control within photonic bandgap for low-loss quantum information processing
Hiroyuki Nihei, Atsushi Okamoto
2007 PACIFIC RIM CONFERENCE ON LASERS AND ELECTRO-OPTICS, VOLS 1-4, 971, 972, IEEE, 2007, [Peer-reviewed]
English, International conference proceedings, We demonstrate the coherent control of an excited atom in photonic crystals, in which its relaxation is strongly suppressed compared with that in the control using the photonic bandgap (PBG) switching. This suggests the possibility of extending the atomic system to a low-loss quantum logic gate for quantum information processing.

Selective erasure of speckle-multiplexed holograms by use of a double Mach-Zehnder interferometric arrangement.
Bunsen M, Furuta H, Okamoto A
Applied optics, 45, 27, 7035, 7042, 27, Sep. 2006, [Peer-reviewed]

Selective erasure of speckle-multiplexed holograms by use of a double Mach-Zehnder interferometric arrangement
Masatoshi Bunsen, Hirosuke Furuta, Atsushi Okamoto
APPLIED OPTICS, 45, 27, 7035, 7042, OPTICAL SOC AMER, Sep. 2006, [Peer-reviewed]
English, Scientific journal, A novel method to selectively erase and update speckle-multiplexed holograms in photorefractive crystals by use of a double Mach-Zehnder (DMZ) interferometric arrangement is presented. The DMZ arrangement automatically produces a pair of Tr-phase-shifted interference patterns used for holographic recording, erasure, and update operations with a fairly simple optical configuration that consists of a commonly used dielectric multilayer beam splitter and two mirrors. The recording and the erasure conditions required for erasing a photorefractive hologram quickly and completely are discussed by calculating the temporal property of the hologram buildup and decay using the time-dependent coupled-wave equations. An experiment is also performed, in which arbitrary holograms in speckle-multiplexed holograms are selectively erased and updated with the simple DMZ optical configuration. (c) 2006 Optical Society of America

All-optical fault-tolerant holographic memory with two photorefractive crystals
M Toishi, A Okamoto, S Honma, K Sato
ELECTRONICS AND COMMUNICATIONS IN JAPAN PART II-ELECTRONICS, 89, 2, 37, 45, SCRIPTA TECHNICA-JOHN WILEY & SONS, 2006, [Peer-reviewed]
English, Scientific journal, The holographic memory with photorefractive crystal may become the next-generation memory because of its superior features of fast speed and huge capacity. However, its problems are the attenuation of recorded information by the erasure effect of light when reading out during reconstruction and the losses due to interference such as external vibrations and impinging light noise. Therefore, in this paper, we propose a fault-tolerant holographic memory having an all-optical nondestructive function and an automatic repair function for recording data. This memory can hold information for a long time by arranging two photorefractive crystals in series and alternately writing from one crystal to the other, and has a function for automatically repairing damage in one part of the hologram caused by some kind of interference. By applying this method, an all-optical fault-tolerant function can be implemented without using a conventional electronic control system. In this paper, we verify the operating principles of recording, reconstruction, and hologram repair by numerical analysis. Next, we evaluate the time needed to repair a hologram as a function of the size of the dropouts occurring in the memory and their frequency. Finally, we demonstrate the effectiveness of this method by performing operating tests of this memory using two-dimensional images. (c) 2006 Wiley Periodicals, Inc.

Theoretical and experimental studies of hologram multiplexing that uses a random wave front generated by photorefractive beam fanning.
Bunsen M, Okamoto A
Applied optics, 44, 8, 1454, 1463, 8, Mar. 2005, [Peer-reviewed]

Photorefractive connection module with organic photorefractive polymer PATPD
K Harasaka, A Okamoto, M Bunsen, M Yamamoto
2005 PACIFIC RIM CONFERENCE ON LASERS AND ELECTRO-OPTICS, 807, 808, IEEE, 2005, [Peer-reviewed]
English, International conference proceedings, We propose an all-optical switching device, photorefractive connection module (PRCM), with an organic photorefractive polymer PATPD. Spatially multiplexed time-series signals propagating in optical bus line can be branched by illuminating matrix patterned control beams.

Spatial spread-spectrum multiplexing for holographic data storage using random diffuser and circular spatial filter
Terumasa Ito, Atsushi Okamoto
Conference on Lasers and Electro-Optics Europe - Technical Digest, 2005, [Peer-reviewed]
English, International conference proceedings

Optical security switch based on spatially phase matching in photorefractive media
Atsushi Okamoto, Hisatoshi Funakoshi, Masatoshi Bunsen, Terumasa Ito, Kunihiro Sato
Conference on Lasers and Electro-Optics Europe - Technical Digest, 2005, [Peer-reviewed]
English, International conference proceedings

Coherent control of spontaneous emission near a photonic band edge using a dark line in emission spectra
Hiroyuki Nihei, Atsushi Okamoto
Conference on Lasers and Electro-Optics Europe - Technical Digest, 2005, [Peer-reviewed]
English, International conference proceedings, We demonstrate that spontaneous emission near a photonic band edge is coherently changed between suppressed emission and enhanced emission using phase controllable-dark lines in spectra, which may provide fundamental functions in quantum data processing. © 2005 IEEE.

Optical image cross connector with multiple-layered photo refractive polymers
Hidenobu Muranaka, Atsushi Okamoto, Shunsuke Uemura, Masatoshi Bunsen, Akinori Nishio
Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest, 2005, 1388, 1389, 2005, [Peer-reviewed]
English, International conference proceedings, We propose an image cross connector with multiple-layered photorefractive polymers that arbitrarily changes and interconnects vertically-disposed input images into horizontally without blur. We verify its fundamental operation with a photorefractive polymer PATPD experimentally.

Long-term retrieving experiment on rewritable holographic memory with dynamic refreshment by mutual-pumped phase conjugator
H Funakoshi, A Okamoto, K Sato
Holography, Diffractive Optics, and Applications II, Pts 1 and 2, 5636, 589, 596, SPIE-INT SOC OPTICAL ENGINEERING, 2005, [Peer-reviewed]
English, International conference proceedings, In this paper, we demonstrate long-term readout in a photorefractive memory with a dynamic refreshment technique by mutual-pumped phase conjugate mirror (MPPCM). The dynamic refreshment means that a volatile hologram is sustained in parallel with its reconstruction by only all-optical process. A simple optical feedback circuit for hologram sustainment by MPPCM is added on to a photorefractive memory in our dynamic refreshment technique. By continuously rewriting with feedback of reconstructed image, long-term continuous readout of a volatile hologram can be realized. This technique with MPPCM also offers grayscale-to-binary conversion by the beam resonance and intensity thresholding of MPPCM that it cannot be built up where the intensity is lower than the threshold level. By adjusting the proper threshold value, therefore, a noise-reduced binary image can be retrieved without any external processing systems. Moreover, high quality output data can be obtained because phase distortion on the image can be automatically removed by optical phase conjugation. This technology is applicable to recording technique such as angular and phase-code multiplexing and allows long-term readout of multiple holograms by the appropriate refreshing schedules. We perform the experiment on long-term readout using barium titanate (BaTiO3) crystals and demonstrate a recorded image is reconstructed over 1 hour with our technique whereas a reconstructed image fades away within 5 minutes with conventional readout technique.

Security improvement with multiplexing for optical encryption based on cross-correlation of random phase masks
K Moritake, A Okamoto, H Funakoshi, T Ito
2005 PACIFIC RIM CONFERENCE ON LASERS AND ELECTRO-OPTICS, 55, 56, IEEE, 2005, [Peer-reviewed]
English, International conference proceedings, Optical random phase encryption methods have the vulnerability of decoding by readout with only a part of correct key. To overcome this vulnerability, we propose a new method by multiplexing original data and dummy data.

All-optical wavelength demultiplexer with photorefractive grating array
T Yagai, A Okamoto, M Bunsen
NONLINEAR OPTICAL PHENOMENA AND APPLICATIONS, 5646, 260, 268, SPIE-INT SOC OPTICAL ENGINEERING, 2005, [Peer-reviewed]
English, International conference proceedings, We propose an all-optical demultiplexer with grating array in a photorefractive crystal to achieve high density board-to-board optical interconnects with wavelength division Multiplexing (WDM). WDM signal emitted from a board can be branched for each wavelength component and the components are connected to different spatial ports by this demultiplexer mounted on another board. Index gratings, which are induced by illumination of two control beams, are aligned spatially along the signal beam line in a photorefractive crystal. The wavelength component of WDM signal is diffracted by an index grating only when the phase-matching condition is satisfied. This condition is determined by incident angles of control beams and the wavelength of the signal beam. By setting incident angles of control beams appropriately, it can be determined whether a wavelength component of WDM signal is diffracted by the index grating or not. The component can be connected to the desirable Output port by arraying the gratings with different grating vector. In Our previous Study, we have shown that this demultiplexer can branch WDM signal for each wavelength component. In this report, we show that the wavelength selectivity of 0.2 nm can be achieved by optimizing the angles of input beams in this demultiplexer. Moreover, we propose a new system in which WDM signal is branched for each wavelength component by angularly multiplexed gratings. By using this Multiple grating we can prevent demultiplexer module from growing in size with increasing the Multiplicity of signal beam unlike grating array.

All-optical interconnection with mutually pumped four-wave mixing and optimization for high connection efficiency
S Honma, S Muto, A Okamoto
HOLOGRAPHY, DIFFRACTIVE OPTICS, AND APPLICATIONS II, PTS 1 AND 2, 5636, 685, 694, SPIE-INT SOC OPTICAL ENGINEERING, 2005, [Peer-reviewed]
English, International conference proceedings, All-optical interconnections are expected to play an important role in optical computing and neural network systems. Some schemes of the interconnection with a mutually pumped phase conjugate mirror (MPPCM) have been proposed. But it takes long time for reconfiguration of the wiring pattern because the competition among a lot of the index gratings induced by the incident beam and its scattered beams forms MPPCM gradually. In this report, we propose a new optical interconnection by using mutually pumped four-wave mixing (MP-FWM) which is composed of a MPPCM and a degenerate four-wave mixing (FWM). In this method, the two control beams induce the hologram that determines the wiring pattern of the signal beams in the FWM region. On the other hand, the signal beams are transferred to the phase conjugate beam of the one of the control beam through the FWM region by using MPPCM and then the signal beams are diffracted to the desired output channels by the hologram in the FWM region. This scheme can reduce the time to reconfigure the wiring pattern remarkably compared with the conventional interconnection using only MPPCM because the hologram can be reformed by the two control beam arbitrarily. It also can suppress the channel crosstalk that is often generated by the photorefractive fanning effect. This interconnection is effective method to solve the problems of the electrical wiring techniques such as the electro-magnetic interference and the thermal generation. We give the experimental result by using BaTiO3 crystal and Ar+ laser, and investigate the optimum condition of the beams for high connection efficiency.

Experiment on selective erasure for multiplexed holograms by using photorefractive phase-shift
T Sano, A Okamoto, K Sato, M Bunsen
2005 PACIFIC RIM CONFERENCE ON LASERS AND ELECTRO-OPTICS, 579, 580, IEEE, 2005, [Peer-reviewed]
English, International conference proceedings, We propose a method of the selective erasure for multiplexed holograms by using photorefractive phase-shift. This method realizes the complete selective erasure with simple operation. We conduct an experiment on selective erasure with two LiNbO3:Fe.

Quantum-information detection from optical memory using photonic crystals
Hiroyuki Nihei, Atsushi Okamoto
Electronics and Communications in Japan, Part II: Electronics (English translation of Denshi Tsushin Gakkai Ronbunshi), 87, 8, 10, 19, Aug. 2004, [Peer-reviewed]
English, Scientific journal, There is now great interest in optical memory using a three-level atom embedded in photonic crystals, which can be used for quantum computing
however, quantum-information detection from the optical memory has not been demonstrated. In this paper, first, considering the relative position of the photonic band gap (PBG) and two atomic levels split from the upper level of the atom used for the optical memory, we demonstrate that one of the split levels must be outside the PBG for quantum-information detection. In this case, the quantum state of the atom can be changed by moving the other split level, where the quantum information is maintained or emitted for the cases in which the split level is inside or outside the PBG, respectively. The emitted quantum information can be measured as spontaneous emissions by a photon detector. Next, we propose two methods of moving the split level: one is realized by applying a direct current (DC) field to the atom and the other is realized by changing the intensity of the control laser field. Furthermore, by evaluating the intensities of the DC and the control laser fields, we find that the quantum information can be measured using the fields on the millielectronvolt order. © 2004 Wiley Periodicals, Inc.

Spontaneous emission from a three-level atom embedded in anisotropic photonic band gap structures
Hiroyuki Nihei, Atsushi Okamoto
Journal of Modern Optics, 51, 13, 1983, 1998, 2004, [Peer-reviewed]
English, Scientific journal, We investigate spontaneous emissions from a three-level atom embedded in realistic anisotropic photonic band gap structures, where the band edge is assumed to be midway between the two upper levels of the atom. In the anisotropic model, the atom-field interaction is reduced to be smaller than that in the ideal isotropic model, which results in the reduction of suppression and oscillation effects in the spontaneous emission
however, we demonstrate that the suppression is strongly enhanced even in the anisotropic model by expanding the detuning between the upper level and the band edge, while the oscillation is greatly reduced. This demonstration is carried out by calculating the atomic state vector for a wide range of the detuning. Using the state vector, the atom-field interaction is studied for two field parts, a localized part and a propagating part, separately. For the localized part, the atom-field interaction is enhanced by expanding the detuning, in spite of the anisotropy, which leads to a strong suppression effect, while for the propagating part, the atom-field interaction is reduced, which leads to a weak oscillation effect. This result is relevant to strong memory effects with high-speed switching, which are attractive properties for a qubit. © 2004 Taylor &
Francis Group, LLC.

Noise reduction in photorefractive memory by double mutually pumped phase conjugate mirrors
H Funakoshi, A Okamoto
ADVANCED OPTICAL AND QUANTUM MEMORIES AND COMPUTING, 5362, 99, 106, SPIE-INT SOC OPTICAL ENGINEERING, 2004, [Peer-reviewed]
English, International conference proceedings, In this report, we demonstrate a noise reduction recording in a photorefractive memory with a dynamic refreshing technique by mutually pumped phase conjugate mirrors (MPPCMs). The dynamic refreshing, that means the continuous rewriting of an original hologram with the optical feedback in synchronism with the readout, largely contributes to the maintenance of the recorded hologram by all-optical process. Long-term continuous readout without any fixing technique can be achieved by the high quality image refreshing that uses the resonance of the phase conjugate beams with image information between phase conjugate mirrors. Our technique additionally offers the noise reduction of an input image in the recording process without any external image processing systems. The noise reduction can be achieved by the characteristics of the MPPCM that the incident intensity ratio required for the MPPCM generation is determined by the coupling strength of the crystal. In this report, we show the noise reduction for an image data and the long-term readout can be realized by adjusting the appropriate incident beam intensities and the coupling strength of crystals. We perform recording and retrieving experiment on the photorefractive holographic memory with barium titanate crystals and demonstrate the noise-reduced image is reconstructed over 10 minutes in the double MPPCM configuration we propose whereas reconstructed image fades away within 2 minutes in the single MPPCM configuration.

All-optical interconnection with cross polarized double phase conjugate mirror
S Uemura, A Okamoto, S Honma
OPTICAL COMPONENTS AND MATERIALS, 5350, 234, 242, SPIE-INT SOC OPTICAL ENGINEERING, 2004, [Peer-reviewed]
English, International conference proceedings, We propose an all-optical interconnection with cross-polarized double phase conjugate mirrors (CP-DPCMs). In the interconnection, spatially arrayed signal beams from an input port two-dimensionally intersect with control beams from an output port in the photorefiractive crystal (PRC) where polarizations of these two beams are orthogonal each other. The CP-DPCM can function as the switching element by adjusting the intensity ratio of these two beams because it strongly depends on the intensity ratio of crossing two beams whether the CP-DPCM is built up in the PRC or not. Thus the signal beam is diffracted by the CP-DPCM and propagated to the output port, when the intensity ratio of signal beam and control beam is adjusted to proper value for buildup of the CP-DPCM. This technique offers the point-to-point interconnection in two-dimensional plane. It implies the possibility of miniaturization and the integration by stacking the planes with different wiring pattern in layers compared to the conventional interconnections with DPCMs. For configuring the arbitrary wiring pattern, it is important to determine the intensities of the signal beams and the control beams, so we investigate the optimum intensities of these beams for effective switching. We carry out basic experiment on 1x2 interconnection with BaTiO3 and Ar+ laser.

Effect of random phase mask on input plane in photorefractive authentic memory with two-wave encryption method
A Mita, A Okamoto, H Funakoshi
ADVANCED OPTICAL AND QUANTUM MEMORIES AND COMPUTING, 5362, 61, 68, SPIE-INT SOC OPTICAL ENGINEERING, 2004, [Peer-reviewed]
English, International conference proceedings, Two-wave encryption method has the feature that the output data are transformed into white-noise data with extremely low intensity in the retrieving process with the incorrect key. In this method, the random phase mask on the input plane plays important roles in prohibiting decryption from a white-noise data to the original image by the blind deconvolution method. Blind deconvolution method is for obtaining the original image from white-noise data by iterative operation. Without this mask, when unauthorized users observe the output beam by using CCD in the readout with the plane wave, the completely same intensity distribution as that of Fourier transform of the original image is obtained. Therefore the encrypted image will be decrypted easily. However in using this mask, even if unauthorized users observe the output beam using the same method, the encrypted image cannot be decrypted because the observed intensity distribution is dispersed at random by this mask. Thus the high security authentic memory system can be realized by using this mask. In the double phase encryption method, data can be protected by transforming the original data into white-noise data with two random phase masks on the object beam. Our encryption method has the additional function that unlawful access is easily detectable because the output beam intensity significantly falls down by unlawful access. However it has not been investigated about randomness of this mask required to make this encryption method operate efficiently. In this report, we investigate the randomness of this mask required to realize the high security memory system by simulation with various input plane phase masks. We show the security of this encryption method can be drastically improved as the correlation coefficient between the original image and the output image decreases from 0.3 to 0.1.

All-optical interconnection with photorefractive grating array for wavelength divided multiplexing signal
T Yagai, A Okamoto, M Bunsen
OPTICAL COMPONENTS AND MATERIALS, 5350, 81, 88, SPIE-INT SOC OPTICAL ENGINEERING, 2004, [Peer-reviewed]
English, International conference proceedings, We propose an all-optical free-space interconnection with a photorefractive grating array for wavelength division multiplexing (WDM) signal. Input WDM signal propagating on free-space can be branched for each wavelength component and the components are connected to different spatial ports by this interconnection. The wavelength component of WDM signal is diffracted by one index grating, which is induced by two control beams, only when the phase-matching condition is satisfied. The phase-matching condition is determined by incident angles of control beams and the wavelength of the signal beam. By setting incident angles of control beams appropriately, it can be determined whether a wavelength component of WDM signal is diffracted by the index grating or not. The component can be connected to the desirable spatial output port by arraying the gratings with different grating vector. We analyze the diffraction efficiency to investigate the wavelength selectivity of this interconnection and investigate the influence of the multiplicity of the signal beam on the diffraction efficiency. As the results, the wavelength selectivity 0.7[nm], which is equivalent to that of the conventional arrayed-waveguide grating, is achieved when the waveband is 500-520[nm]. Moreover the diffraction efficiency 0.055 is obtained when the degree of multiplexing is 50.

Hologram multiplexing method with photorefractive beam-fanning speckle
M Bunsen, A Okamoto
ADVANCED OPTICAL AND QUANTUM MEMORIES AND COMPUTING, 5362, 128, 135, SPIE-INT SOC OPTICAL ENGINEERING, 2004, [Peer-reviewed]
English, International conference proceedings, We suggest a hologram multiplexing method with speckled reference beams generated by the photorefractive beam-fanning effect. In this method, speckled reference beams are generated in a storage photorefractive crystal without external diffusers. The speckled reference beams to record multiple holograms can be obtained by changing spatial intensity distribution, spatial phase distribution, incident angle or incident position of the original reference beam. We first analyze propagation of the fanning beam in the photorefractive crystal, and discuss the optimum orientations of the photorefractive crystal and incident beams to implement the hologram multiplexing. We also demonstrate the hologram multiplexing and retrieving with the speckled reference beam generated by the beam-fanning effect in a photorefractive barium titanate crystal. Here, we vary the speckle field by changing the incident position of the original reference beam. Six holograms are multiplexed in a barium titanate crystal, and stored images are successfully reconstructed. These results indicate that this method has the great possibility for all-optical control of hologram multiplexing, besides simplification of the optical configuration comparing with the conventional speckle multiplexing schemes using a ground glass, a multimode optical fiber and so on.

Stabilization of signal beam intensity for fault-tolerant automatic routing with double phase conjugate mirrors
H Kato, A Okamoto, M Bunsen
EMERGING OPTOELECTRONIC APPLICATIONS, 5363, 148, 155, SPIE-INT SOC OPTICAL ENGINEERING, 2004, [Peer-reviewed]
English, International conference proceedings, We have proposed a fault-tolerant automatic routing method with two photorefractive double phase conjugate mirrors (DPCMs) for free space optical communication by now. In this method, a signal beam can be all-optically and automatically switched from a main line to a backup line when the main line is shut off by obstacles. The optical link between a transmitter and a receiver is kept without any electronic devices and complex optical configuration because the adequate communication line is automatically selected by two DPCMs which are generated by the signal beam and support beams in one photorefiractive crystal. In this report, we equalize the signal beam intensities on the main line and the backup line to increase the reliability of communication. If a coupling strength ratio between two DPCMs is inappropriate, the signal beam intensities on both lines become inequality and this induces the increase of the bit error rate in beam detection. Therefore, it is necessary to adjust the signal beam intensities by changing the coupling strength ratio between two DPCMs. We show that the signal beam intensities on both lines can be equalized completely by using the optimum coupling strength ratio between two DPCMs, e.g. about 1.28 in BaTiO3 crystal.

Experiment on two-dimensional data restoring in fault-tolerant holographic memory
T Ito, A Okamoto, H Funakoshi
ADVANCED OPTICAL AND QUANTUM MEMORIES AND COMPUTING, 5362, 111, 118, SPIE-INT SOC OPTICAL ENGINEERING, 2004, [Peer-reviewed]
English, International conference proceedings, Fault-tolerant holographic memory (FTHM) composed of a pair of photorefractive crystals are proposed. This memory offers not only non-destructive readout but also data restoring function by only pure optical operations without any electrical controls. In recording the same holographic data are simultaneously recorded to two crystals laid out in series. During readout, hologram in one memory is mutually refreshed by a feedback beam that is from a diffraction beam on the opposite crystal. Thus, holograms in both the crystals are all-optically sustainable against erasure effect caused by an exposure of a reading beam. Furthermore, even if a certain fault such as vibration and stray beam incidence happens, the lost data in one crystal are automatically restored as long as the corresponding holographic data remain in the other crystal. An experiment for confirming the restoring function in the FTHM is carried out. A two-dimensional image is recorded into a pair of 45degrees-cut BaTiO3 crystals, and the partially erased hologram in one crystal is successfully restored by the mutual refreshing.

All-optical interconnection device with photorefractive semi-linear resonator
S Honma, A Okamoto
IEICE TRANSACTIONS ON ELECTRONICS, E86C, 10, 2103, 2110, IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG, Oct. 2003, [Peer-reviewed]
English, Scientific journal, We propose and describe a free-space optical interconnection device with a photorefractive semi-linear resonator. The hologram in the photorefractive crystal is, in general, volatile and the erasing of it coincides with the diffraction of the signal beam. Therefore we have to reform the hologram again after several transmissions of the data or use some fixing techniques such as thermal fixing and electrical fixing. In our interconnection device, the hologram is enhanced by the feedback beam that is a part of the input signal divided by the beam splitter within semilinear resonator, therefore the sustentation time of the connection can be extended. We explain the sustentation mechanism and investigate the optimum reflectivity of the beam splitters, which determine the feedback rate of the input signal, within feedback circuit for the high output conversion efficiency. We also analyze the coupling strength threshold for sustentation of the connection. We give a basic experiment on 3 x 3 interconnection by using BaTiO3, crystal and Ar+ laser whose wavelength is 514 [nm]. We show that the connections are held for long time without the continuous illumination of the control beam.

Two-qubit operation of two atoms embedded in photonic crystals for optical quantum computing
H Nihei, A Okamoto
ICTON 2003: 5TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS, VOL 2, PROCEEDINGS, 212, 215, IEEE, 2003, [Peer-reviewed]
English, International conference proceedings, We demonstrate the two-qubit operation of two atoms embedded in photonic crystals, which is realized by applying a small DC field to the atoms according to quantum algorithms.

THz emission from a multifunctional active atomic device in photonic crystals
Hiroyuki Nihei, Atsushi Okamoto
Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest, 1, 320, Institute of Electrical and Electronics Engineers Inc., 2003, [Peer-reviewed]
English, International conference proceedings, We demonstrate that ultrafast emission is obtained from a multifunctional active atomic device using photonic crystals, which can be used for an optical THz oscillator in addition to a memory and a switch.

Optical Encoding for Quantum Computation Using Photonic Crystals
Hiroyuki Nihei, Atsushi Okamoto
Proceedings of SPIE - The International Society for Optical Engineering, 4829, 753, 754, 2003, [Peer-reviewed]
English, International conference proceedings, We demonstrate optical encoding in an atomic device, considered as a key component in quantum computers. The atomic device consists of a three-level atom embedded in photonic crystals without external driving lasers. We find that a large amount of population trapping in the upper levels of the atom can be achieved, which is relevant for a strong optical memory effect. Furthermore, the trapped populations keep a memory of the initial atomic state including two-state quantum information, so that the atomic device can be used for a quantum bit encoding the quantum information.

Experiment on long-term image reading in photorefractive memory with double mutually pumped phase conjugate mirrors
H Funakoshi, A Okamoto, K Sato
ICTON 2003: 5TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS, VOL 1, PROCEEDINGS, 291, 294, IEEE, 2003, [Peer-reviewed]
English, International conference proceedings, We propose a dynamic refreshing technique in a photorefractive memory with double mutually pumped phase conjugate mirrors. Long-term continuous readout without any fixing technique can be achieved by the high quality image refreshing that uses the resonance of the phase conjugate beams with image information between phase conjugate mirrors. We perform the experiment on the long-term reading of the images in the photorefractive memory with BaTiO3 Crystals and achieve the continuous reading time over 10 times longer than the time constant of the crystal without image degradation.

Experiment on hologram multiplexing with photorefractive beam-fanning speckle
M Bunsen, A Okamoto
ICTON 2003: 5TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS, VOL 1, PROCEEDINGS, 287, 290, IEEE, 2003, [Peer-reviewed]
English, International conference proceedings, We propose a hologram multiplexing method with the photorefractive beam-fanning speckle. In this method, a bulk photorefractive crystal takes the role of generating various speckle fields as well as storing a number of holograms. The hologram multiplexing and the selective retrieving are demonstrated with the speckled reference beam generated by the beam-fanning effect in a photorefractive BaTiO3 crystal. The speckle field of the reference beam to record multiple holograms is varied by changing the spatial phase distribution or the intensity distribution of the original reference beam. We can successfully reconstruct the desired image from multiplexed holograms with the reference beam speckled by the beam-fanning effect in both procedures. This method has the potential for the all-optical control of the multiplexing and the selective retrieving from the multiplexed holograms, besides the simplification of the optical configuration comparing with the conventional speckle multiplexing.

Optical memory using photonic crystals without external driving lasers for quantum computation
Hiroyuki Nihei, Atsushi Okamoto
Proceedings of SPIE - The International Society for Optical Engineering, 4923, 132, 139, SPIE, 05 Sep. 2002
English, International conference proceedings, In real photonic band gap (PBG) materials, the PBG is highly anisotropic. In this paper, we propose an optical memory composed of a three-level atom embedded in the realistic anisotropic PBG structures without external driving lasers, which can be considered as essential components for a novel class of computation including an optical quantum computation.

Dynamic dropout data restoring technique in all-optical fault tolerant holographic memory
M Toishi, A Okamoto, K Sato
ADVANCED OPTICAL DEVICES, TECHNOLOGIES, AND MEDICAL APPLICATIONS, 5123, 157, 164, SPIE-INT SOC OPTICAL ENGINEERING, 2002, [Peer-reviewed]
English, International conference proceedings, We have proposed the all-optical fault-tolerant holographic memory (FTHM) that automatically restores the dropout data by the constant rewriting method. In this method, the constant rewriting is conducted in the normal state or dropout state, so this data restoring is inefficient in terms of the restoring speed and the energy consumption. In this paper, we propose a dynamic dropout data restoring technique in the FTHM. In this dynamic technique, the strength of the rewriting effect change in proportion to dropout level, i.e. if dropout level becomes large, the strength of the rewriting effect also becomes large automatically. Therefore, this dynamic technique can improve the restoring speed and reduce the energy consumption for restoring. First, we analyze the temporal response of the output efficiency and the hologram. Next we analyze the dependency of the output efficiency on the coupling strength in the two crystals and the incident condition of two beams, and estimate the coupling strength threshold and the ratio of the incident beams in order to maintain the stored data. Finally, we experiment on the dropout data restoring by using BaTiO3 as photorefractive crystal, and achieve the data restoring for 2-3 seconds and the over 25 minutes readout.

All-optical interconnection with wiring maintenance technique by integrated full-linear resonator
T Mitasaki, A Okamoto, S Honma
ADVANCED OPTICAL DEVICES, TECHNOLOGIES, AND MEDICAL APPLICATIONS, 5123, 165, 171, SPIE-INT SOC OPTICAL ENGINEERING, 2002, [Peer-reviewed]
English, International conference proceedings, We have proposed the all-optical interconnection, in which the photorefractive four wave mixing(FWM) is used as the core, by full-linear resonator(FR) with a beam splitter(BS) and a self-pumped phase conjugate mirror(CAT). The index grating of the FWM region inside the photorefractive crystal (PRC), which determines the connection pattern, was maintained by the rewriting effect of the input signal beam and the resonance beam between the CAT and the BS. But the power of the resonance beam was wasted by the optical reflection at the crystal surface of the CAT and the PRC. Therefore the rewriting effect of the connection pattern could not be obtained sufficiently. In this report, we propose the integrated full-linear resonator(IFR), in which a self-pumped phase conjugation(SPPC) region and the FWM region are formed in one PRC, to solve this problem. Compared with the conventional FR, the power loss of the resonance beam by the optical reflection can be prevented and the resonance beam can be used efficiently for the maintenance of the connection pattern. We experiment on the 2x2 all-optical interconnection with the IFR by using BaTiO3 crystals and Ar+ laser. It is shown that the maintenance time of the connection pattern can be extended sufficiently by using IFR.

Improvement of storage density in photorefractive disk-type memory by logical multilayer recording method.
M Bunsen, A Okamoto, K Sato
ADVANCED OPTICAL STORAGE TECHNOLOGY, 4930, 343, 350, SPIE-INT SOC OPTICAL ENGINEERING, 2002, [Peer-reviewed]
English, International conference proceedings, In this paper, we propose a photorefractive disk-type memory with cross polarized four-wave mixing, and suggest a method to enhance the storage density for this disk-type memory. The shift multiplexing technique, in which the feasible recording of the angularly multiplexed holograms can be implemented by means of the spherical reference beam and the rotation of the disk-shaped crystal, is applied for this memory. We analytically investigate the amounts of shift required for multiplexing differential holograms in this memory, and we carry out an experiment to verify the analytical results. Also we suggest a logical multilayer recording method as the novel scheduled recording method, and analyze the temporal property of cross polarized four-wave mixing to estimate the diffraction efficiencies from the multiplexed holograms with the method. From those analyses, it is revealed that the diffraction efficiency and the storage density of the photorefractive disk-type memory are significantly improved by this method.

Bi-directional cross connector with double phase conjugator and polarization multiplexed control signal
S Honma, A Okamoto
HOLOGRAPHY, DIFFRACTIVE OPTICS, AND APPLICATIONS, 4924, 282, 293, SPIE-INT SOC OPTICAL ENGINEERING, 2002, [Peer-reviewed]
English, International conference proceedings, In this paper, we propose an application of the mutually pumped phase conjugation to the all-optical connection switch and present the two type of the bi-directional cross connector with the photorefractive crystals, the polarized beam splitters and the half-wave plates in terms of the control method. In the type 1 connector, the bypass mode or the exchange mode can be selected by the external control beam whose polarization is orthogonal with those of the signal beams. In the type 2 connector, these modes can be controlled by rotating the polarization of the signal beams. We give the basic experimental result of these connectors with BaTiO3 crystals and Ar+ laser, and discuss about the results.

All-optical bi-directional cross-connector with photorefractive double phase conjugation and control beam
S Honma, A Okamoto
ADVANCED OPTICAL DEVICES, TECHNOLOGIES, AND MEDICAL APPLICATIONS, 5123, 144, 150, SPIE-INT SOC OPTICAL ENGINEERING, 2002, [Peer-reviewed]
English, International conference proceedings, We propose a bi-directional multi-channel cross-connector for two-way optical communications with array of the photorefractive crystal. The communication channels are connected bi-directionally by double phase conjugation in each photorefractive crystal. The wiring pattern is possible to determine by the beam that controls whether it generates the double phase conjugation in the crystal. This all-optical switching is effective method to solve the problems of the electrical wiring techniques such as the electro-magnetic interference and the thermal generation. We analyze the connection efficiency for coupling strength of the two four-wave mixing interaction region in the double phase conjugation and investigate the intensity of control beams for sufficiently switching. We also experiment on the bidirectional connection switch and estimate the connection efficiency and the transmission efficiency.

High performance encryption method and all-optical authentic memory with photorefractive crystal
A Mita, A Okamoto, N Tsuji, M Bunsen
ADVANCED OPTICAL STORAGE TECHNOLOGY, 4930, 351, 358, SPIE-INT SOC OPTICAL ENGINEERING, 2002, [Peer-reviewed]
English, International conference proceedings, We propose an all-optical encryption memory using the photorefractive four wave mixing and random phase masks. In our encryption method, the image data are encrypted to white noise by the phase shift patterns added on the signal beam with the image data and the reference beam through the random phase masks. Only reading beam with the phase-conjugated distribution of the reference beam can restore the encrypted data. If the encrypted data are read out by incorrect phase pattern, the output data can't be obtained because of the wavefront mismatch between the recorded hologram and the reading beam. We evaluate the encryption and decryption process by analyzing the diffraction efficiency with consideration of the angular spectrum. We show that high performance encryption that high contrast and high gradation image data can be decrypted accurately and the output data are perfectly dark by using the incorrect decryption key can be realized theoretically.

Photorefractive nondestructive memory with Kitty-type conjugator
H Funakoshi, A Okamoto
ADVANCED OPTICAL DEVICES, TECHNOLOGIES, AND MEDICAL APPLICATIONS, 5123, 151, 156, SPIE-INT SOC OPTICAL ENGINEERING, 2002, [Peer-reviewed]
English, International conference proceedings, In this report, we propose a photorefractive (PR) nondestructive memory with a Kitty-type phase conjugate mirror (Kitty PCM). Nondestructive readout without any fixing technique and high quality image rewriting can be achieved in this memory. An optical feedback circuit including a Kitty PCM is added on to the usual PR memory in the nondestructive reading method. The nondestructive readout means that the recorded data of the dynamic hologram, generally erased by the exposure of the reading beam, is maintained by only all-optical configuration. The nondestructive readout in this memory is achieved by the hologram rewriting effect that is generated by the re-illumination of the diffraction beam reflected by a phase conjugate mirror. But a conventional Cat-type self-pumped phase conjugate mirror (Cat SPPCM) has insufficient reflectivity to obtain large feedback rate required for this nondestructive readout. In this report, we calculate and experiment on the phase conjugate reflectivity and the time response property of the Kitty PCM and show it has the advantages of high reflectivity and fast response time. We perform the experiment on our rewritable PR memory using BaTiO3 crystals and demonstrate the long time reading over 18 minutes is achieved in this memory.

Fault tolerant all-optical router with photorefractive all-optical switch
T Kaino, A Okamoto, S Honma
ADVANCED OPTICAL DEVICES, TECHNOLOGIES, AND MEDICAL APPLICATIONS, 5123, 172, 178, SPIE-INT SOC OPTICAL ENGINEERING, 2002, [Peer-reviewed]
English, International conference proceedings, We propose a new type of the fault tolerant all-optical router (FTAR) by using an all-optical switch with photorefractive two-wave mixing. FTAR can detect a cutoff of a main transmitting line and automatically reroute a signal beam from the main line to a backup line. These functions can increase communication reliability of optical wireless. FTAR is composed of only all-optical devices without any electronic devices or any mechanical operations. In the new type of FTAR, the routing of the signal beam is controlled by a control beam transmitting on the main line from a different light source at a receiver in the opposite direction with the signal beam. Compared with the previous type of FTAR composed of two photorefractive crystals, the new configuration offers the simplification of the construction and high transmission efficiency of the signal beam. In this report, we experiment on the FTAR by using a BaTiO3 and Ar+ laser whose wavelength is 514.5nm, and confirm the fundamental function of FTAR. We give comparison of the result with the numerical analysis. We also analyze the dependence of the switching time on the input beam intensity of the crystal by a numerical analysis and an experiment.

Information sharing and exchanging in add/drop optical network by double phase conjugator
A Okamoto, K Kori, Y Takayama, S Homma
HOLOGRAPHY, DIFFRACTIVE OPTICS, AND APPLICATIONS, 4924, 311, 321, SPIE-INT SOC OPTICAL ENGINEERING, 2002, [Peer-reviewed]
English, International conference proceedings, We have studied PRCM as a basic device that could achieve a free-space optical communication with the spatial parallelism using mainly photorefractive crystal and four-wave mixing technique. The asynchronous PRCM, which is newly introduced in this paper, has the diffraction grating generated by two control beams independent of the signal beam. Thus, the signal is transmitted at the velocity of light and can be branched with no delay from the multiple nodes connected on the transmission bus line. We also propose a new two-way communication device, to which double phase conjugator technology was applied, as opposed to the one-directional device of optical signals from the transmitting side to the reception side. We conduct a basic evaluation on the branching and transmission characteristics of signals at the spatial optical switch element.

Switching Time of Optical Memory Devices Composed of Photonic Crystals with an Impurity Three-Level Atom
Nihei Hiroyuki, Okamoto Atsushi
Jpn J Appl Phys, 40, 12, 6835, 6840, The Japan Society of Applied Physics, 15 Dec. 2001
English, We calculate the switching time of an optical memory device composed of three-dimensional photonic crystals with an impurity three-level atom, that is, a photonic memory device. We determine the switching time to be a function of the overshoot and the time constant of a decaying oscillation of the upper level population of the impurity atom. The analytical solutions for the overshoot and the time constant are given by using the Euler approach. Using these functions, we calculate the switching time for the Rabi frequency and the transition frequency of the impurity atom. Our results show that the switching time is improved by changing the transition frequency from inside the photonic band gap to outside it and/or by increasing the Rabi frequency, where the transition frequency and the Rabi frequency can be controlled by a small power field. We determine suitable ranges of these frequencies for realizing a high-speed photonic memory device, which are important for atomic-scale optical systems such as high-density integrated optical circuits and quantum computers.

Photorefractive duplex two-wave mixing and all-optical deflection switch
S Honma, A Okamoto, Y Takayama
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS, 18, 7, 974, 981, OPTICAL SOC AMER, Jul. 2001, [Peer-reviewed]
English, Scientific journal, We propose and demonstrate an all-optical deflection switch with photorefractive duplex two-wave mixing (TWM) in which common grating is shared by the TWM of the two control beams and that of signal beams in a photorefractive crystal. TWM occurs both with the signal beams and with the control beams. By calculating the output intensities of the signal beams, we show that the output intensities of the signal beams are controllable by use of the phase difference of the control beams. We analyze the practical ratio of the intensities of the control beams to those of the signal beams for effective switching. A comparison of the numerical analysis with a basic experiment is given. Qualitative agreement is exhibited. (C) 2001 Optical Society of America.

Long-time optical oscillating effects in a three-level atomic system placed within photonic crystals　　　　　　　　　　　　　　　
Hiroyuki Nihei, Atsushi Okamoto
Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest, 2, II344, II345, 2001
English, International conference proceedings, Long-time optical oscillating effects in a three level atomic system placed within 3-dimensional photonic crystals were demonstrated. The effects produced periodical spontaneous emission, which is applicable to optical functional devices, such as optical clocks. The frequency of the optical clock showed linear dependence on a relatively strong continuous wave laser field.

All-optical switching scheme using a three-level atomic system within photonic crystals
Hiroyuki Nihei, Atsushi Okamoto
Proceedings of SPIE - The International Society for Optical Engineering, 4598, 217, 224, 2001, [Peer-reviewed]
English, Scientific journal, We propose all-optical switching schemes using a single three-level atomic system placed within a 3D photonic crystal that exhibits a complete 3D photonic band gap. The optical schemes we propose can be classified into two types with respect to a physical process that causes the switching effect. One switching type is mediated by changing an atom-field coupling strength. The other switching type is mediated by controlling quantum interference. Furthermore, we consider conditions of realizing a wide range of signals, which contributes to an improvement of the Signal to Noise ratio. The phases and strengths of the external laser fields required for the all-optical switching are revealed. Next, we estimate their switching times. Using these results, we propose the fastest scheme for every configuration of the atomic system, which is important for realizing a high-speed optical memory or switching device on an atomic scale that can be used in novel optical integrated systems, such as quantum computers.

Photonic crystal systems for high-speed optical memory device on an atomic scale
Hiroyuki Nihei, Atsushi Okamoto
Proceedings of SPIE - The International Society for Optical Engineering, 4416, 470, 473, 2001, [Peer-reviewed]
English, Scientific journal, Photonic crystal systems were studied for high-speed optical memory devices on an atomic scale. The switching time of the photonic memory devices was investigated for several switching schemes. From the comparison of switching times, it was found that the switching scheme in which the switching was mediated by the application of small dc field was the fastest.

Fault-tolerant system using all-optical sensing and feed back circuits
A Okamoto, S Honma, T Kaino, M Toishi
OPTICAL ENGINEERING FOR SENSING AND NANOTECHNOLOGY (ICOSN 2001), 4416, 396, 399, SPIE-INT SOC OPTICAL ENGINEERING, 2001, [Peer-reviewed]
English, International conference proceedings, This study suggests an optical fault-tolerant system using all-optical sensing and feed back circuits with photorefractive crystals. The first example is a fault-tolerant system in which the system independently detects a cutoff of the optical transmission line and converts its routing to the backup line. Next, while practical application of holographic optical memory is currently being developed, under proposing system, the memory system automatically detects the loss of information (dropout) in optical memory, and reloads and eventually restores the corresponding data from the back-up memory.

Experiment on automatic data duplication in all optical holographic memory
M Toishi, A Okamoto, K Sato, H Funakoshi
PHOTONICS TECHNOLOGY IN THE 21ST CENTURY, 4598, 200, 207, SPIE-INT SOC OPTICAL ENGINEERING, 2001, [Peer-reviewed]
English, International conference proceedings, In this report, we study the automatic data duplication function in an all-optical fault tolerant holographic memory with two photorefractive crystals. In this memory, when a partial data are dropout, the dropout event is detected and the dropout data are restored automatically without any electronic device. We analyze the dependency of the data restoring performance on the frequency of dropout event. We calculate the MTTR (Mean Time To Recovery), in case the data in one crystal are dropout, then the data in another crystal are also lost before the dropout data haven't been completely yet. On the assumption that the data in one of the crystal are dropout, we conduct the experiment in the data recovery on this memory to examine the performance of restoring the data. We achieve that the MTTR is 1seconds and the data are continuously readout over 550 seconds when the stored data in one of the crystal are lost.

All-optical interconnection with pattern memory function by photorefractive full-linear resonator
T Mitasaki, A Okamoto, S Honma
PHOTONICS TECHNOLOGY IN THE 21ST CENTURY, 4598, 225, 232, SPIE-INT SOC OPTICAL ENGINEERING, 2001, [Peer-reviewed]
English, International conference proceedings, We propose an all-optical interconnection with pattern memory function by a photorefractive full-linear resonator with a beam splitter(BS) and a self-pumped phase conjugate mirror(CAT). This interconnection utilizes the oscillation phenomenon between the BS and the CAT. This resonance beam rewrites and sustains the connection pattern continuously, which is once configured by the writing beam, after the writing beam is turned off. We analyze the optimum reflectivity of the BS and the CAT, which determines the feedback rate of the resonation, for high connection efficiency. We also analyze the coupling strength threshold of the photorefractive crystal for the sustentation of the connection. We experiment on the photorefractive fall-linear resonator in order to examine the efficiency and the sustentation time of the connection.

Fault-tolerant holographic memory with two photo refractive crystals
M Toishi, A Okamoto, S Honma, M Bunsen
CLEO(R)/PACIFIC RIM 2001, VOL II, TECHNICAL DIGEST, 160, 161, IEEE, 2001, [Peer-reviewed]
English, International conference proceedings, We propose an all-optical fault-tolerant holographic memory with two photorefractive crystals. The memory system can automatically detect "dropout" data and rewrite a corresponding data from tire back up crystal. We analyze the temporal response of the memory, and show how tire dropout data are restored automatically([1]).

Image reading and writing experiment on photorefractive nondestructive memory
H Funakoshi, A Okamoto, K Sato
PHOTONICS TECHNOLOGY IN THE 21ST CENTURY, 4598, 193, 199, SPIE-INT SOC OPTICAL ENGINEERING, 2001, [Peer-reviewed]
English, International conference proceedings, In this report, we experiment on the two-dimensional image reading and writing in the photorefractive nondestructive memory with BaTiO3 crystal. The great extension of the reading time is archived by use of the grating maintenance technique with optical feedback. By calculating the temporal property of the output beam intensity and the index grating amplitude under the incident conditions of the conventional readout technique and our readout technique, we estimate the feedback rate and the coupling strength for high output generating efficiency. We experiment on the two-dimensional image reading and writing with BaTiO3 crystal, and succeed at over 20 minutes reading without image degradation.

Operable conditions of the beam-fanning novelty filter for the c axis and the incident angle
T Yoshida, A Okamoto, Y Takayama, K Sato
APPLIED OPTICS, 39, 32, 5940, 5948, OPTICAL SOC AMER, Nov. 2000, [Peer-reviewed]
English, Scientific journal, We analyze the operable angle range of the c axis and the incident angle of the input beam in the beam-fanning novelty filter (BFNF). With Fourier transforms we show the analysis method for the beam-fanning phenomenon. We investigate the beam-fanning phenomenon for not only the c axis but also the incident angle of the input beam in order to operate the BFNF sufficiently. Consequently, we clarify the angle range of the c axis and the incident angle, from which sufficient strong beam-fanning effect can be obtained to operate the BFNF. In addition, we verify the numerical results experimentally. (C) 2000 Optical Society of America OCIS codes: 070.2590, 100.2440, 190.5330, 230.4320.

Experiment on all-optical switch with photorefractive duplex two-wave mixing　　　　　　　　　　　　　　　
Satoshi Honma, Atsushi Okamoto, Kunihiro Sato
Conference on Lasers and Electro-Optics Europe - Technical Digest, 156, IEEE, 2000
English, International conference proceedings, An all optical switch controlled by the phase difference between two control beams with photorefractive duplex two wave mixing is proposed. By adjusting the phase difference between control beams, control of energy transfer was made. It was found that switching rate could be improved with an optical setup.

Optimization of multiplexing scheme in photorefractive disk-type memory　　　　　　　　　　　　　　　
Masatoshi Bunsen, Atsushi Okamoto, Kunihiro Sato
Conference on Lasers and Electro-Optics Europe - Technical Digest, 125, IEEE, 2000
English, International conference proceedings, The storage density in the photorefractive disk type memory can be enhanced by means of a combination of cross polarized four wave mixing and two-dimensional shift multiplexing. It is shown that memory signals can be multiplexed at the same spot of the magnetic disk. High storage density on the memory is realized with this characteristic. An optimization approach is proposed, which provides remarkable enhancements in the degree of multiplexing and the storage density.

Optical demodulator with photorefractive cross polarized duplex two-wave mixing
S Honma, A Okamoto, Y Takayama
OPTICS IN COMPUTING 2000, 4089, 867, 875, SPIE-INT SOC OPTICAL ENGINEERING, 2000, [Peer-reviewed]
English, International conference proceedings, We propose an optical demodulator with photorefractive cross-polarized duplex two-wave mixing, in which the phase-modulated signal beam is converted into the intensity-modulated output signal beams. We calculate the intensity variations of the output signal beams when phase-modulated signal beam input to photorefractive cross-polarized duplex two-wave mixing.

Enhancement of storage density in photorefractive disk-type memory with cross polarized four-wave mixing
M Bunsen, A Okamoto, K Sato
OPTICS IN COMPUTING 2000, 4089, 806, 814, SPIE-INT SOC OPTICAL ENGINEERING, 2000, [Peer-reviewed]
English, International conference proceedings, In this paper, we propose the enhancement technique of the storage density in the disk-type memory with photorefractive cross polarized four-wave mixing. We calculate the amounts of shift that enable us to distinguish adjacent signals in the directions of the circle and the radius of the disk, and we carry out experiments to verify the analytical results. Also we investigate the temporal property of cross polarized four-wave mixing to estimate the optimum exposure time.

PRCM and its optical bus application by photorefractive four-wave mixing with cross polarization pumping　　　　　　　　　　　　　　　
Atsushi Okamoto, Kentaro Watanabe, Hisashi Matsuoka, Yoshihisa Takayama
Proceedings of SPIE - The International Society for Optical Engineering, 3740, 450, 453, Society of Photo-Optical Instrumentation Engineers, 1999
English, Scientific journal, The branching gain for extraction of data and the bus gain of photorefractive connection module (PRCM) with cross polarized four-wave mixing in a photorefractive crystal from the point of view of pump ratio optimization is analyzed. The stationary and temporal responses of two-stage-connected PRCM composed by BaTiO3 crystals are measured and a light controlled optical image bus system are proposed.

Cross-polarized photorefractive four-wave mixing with extraordinary writing beams and an ordinary reading beam
Yoshihisa Takayama, Atsushi Okamoto, Motoki Saito, Kunihiro Sato
Applied Optics, 37, 14, 2967, 2973, 10 May 1998, [Peer-reviewed]
English, Scientific journal, In parallel-polarized photorefractive four-wave mixing the phase-matching condition can be achieved automatically if the pump beams are allowed to propagate in directions opposite to each other. However, in cross-polarized photorefractive four-wave mixing, the incident angles of the beams should be adjusted to maintain the phase-matching condition. We analyze the phase-matching properties of cross-polarized four-wave mixing with extraordinary writing beams and an ordinary reading beam and obtain the phase-conjugate reflectivity in consideration of phase mismatching. We also perform an experiment in which a phase-conjugate beam is generated in cross-polarized four-wave mixing and confirm the analyses. © 1998 Optical Society of America.

Cross-polarized photorefractive four-wave mixing with extraordinary writing beams and an ordinary reading beam
Y Takayama, A Okamoto, M Saito, K Sato
APPLIED OPTICS, 37, 14, 2967, 2973, OPTICAL SOC AMER, May 1998, [Peer-reviewed]
English, Scientific journal, In parallel-polarized photorefractive four-wave mixing the phase-matching condition can be achieved automatically if the pump beams are allowed to propagate in directions opposite to each other. However, in cross-polarized photorefractive four-wave mixing, the incident angles of the beams should be adjusted to maintain the phase-matching condition. We analyze the phase-matching properties of cross-polarized four-wave mixing with extraordinary writing beams and an ordinary reading beam and obtain the phase-conjugate reflectivity in consideration of phase mismatching. We also perform an experiment in which a phase-conjugate beam is generated in cross-polarized four-wave mixing and confirm the analyses. (C) 1998 Optical Society of America.

Bistability control by forward pump beam in photorefractive four-wave mixing
Y Takayama, A Okamoto, K Sato
ELECTRONICS AND COMMUNICATIONS IN JAPAN PART II-ELECTRONICS, 81, 2, 1, 8, SCRIPTA TECHNICA-JOHN WILEY & SONS, Feb. 1998, [Peer-reviewed]
English, Scientific journal, A typical method of generating phase conjugate light using photorefractive crystals is four-wave mixing. It is known that the phase conjugate reflectivity is multivalued in a steady state. In this paper, a time domain response analysis of four-wave mixing is carried out and the method for controlling the bistability of the phase conjugate reflectivity is described. First, a steady-state analysis of the four-wave mixing is carried out and the condition is derived for bistability of the phase conjugate reflectivity. Next, by using two different initial conditions, the time response analysis is carried out for the four-wave mixing. Under one of the conditions, no forward pump beam is incident before and after observation of the bistability for measurement of phase conjugate reflectivity. Under another condition, the forward pump is incident before observation of the bistability. The phase conjugate reflectivity is measured after this pump is cut off when a steady state is reached. For each case, the numerical calculations are carried out. It is shown for the first time that the bistability of the phase conjugate reflectivity can be controlled by the initial condition. Further, the temporal and spatial variations of the diffraction grating generated in the crystal are studied and the process of the phase conjugate reflectivity to exhibit bistability is clarified. (C) 1998 Scripta Technica.

Study on optimum incident angles of cross polarized four-wave mixing with a photorefractive crystal
Y Takayama, A Okamoto, K Sato, K Kumagai, Y Aizawa
OPTICAL REVIEW, 5, 1, 49, 53, OPTICAL SOC JAPAN, Jan. 1998, [Peer-reviewed]
English, Scientific journal, We consider the optimum incident angles of cross polarized four-wave mixing with a photorefractive crystal. First, the phase matching angles are obtained for two operation modes: one in which the writing beams are ordinary rays and the reading beam is an extraordinary ray, we call this Mode 1. The other in which the writing beams are extraordinary rays and the reading beam is an ordinary ray, Mode 2. Next, practicable ranges of the incident angles are calculated considering of the total internal reflection of the phase conjugate beam in cases where the two writing beams illuminate the same surface of the BaTiO(3) crystal and where they illuminate the neighboring right-angled surfaces, respectively. Then, the coupling coefficient is determined as a function of the incident angle, and the optimum incident angles for effective beam interaction in Mode 1 and Mode 2 are estimated.

FOURIER OPTICAL ANALYSIS OF IMAGE UPCONVERTER : IN THE CASE OF PLANE WAVE PUMPING
OKAMOTO Atsushi, SATO Kunihiro, MISHIMA Teruhito, SAKURABA Ichiro
ITE Technical Report, 11, 8, 1, 6, The Institute of Image Information and Television Engineers, 1987
Japanese, Coupled wave equations of two-photon-resonant image upconverter and their approximate solutions for plane wave pumping are derived from Maxwell's equations in spatial frequency domain. In the case of plane wave pumping, the image upconverter can be characterized by the extension of optical transfer function (OTF). If the media is thin enough, the OTF has the only phase factor from that the image formations are derived. But if it is thick, the phase mis-matching and the interaction strength affect the conversion efficiency and spatial frequency dependence of the efficiency.

Improvement of Diffraction Efficiency of Mode Demultiplexer Using Volume Hologram at 1550nm
柴 泰純, 岡本 淳, 林 穂高, 小川 和久, 富田 章久, 高畠 武敏, 後藤 優太, 品田 聡, 和田 尚也, 電子情報通信学会技術研究報告 = IEICE technical report : 信学技報, 119, 231, 105, 108, 17 Oct. 2019
電子情報通信学会, Japanese

Improvement of Diffraction Efficiency of Mode Demultiplexer Using Volume Hologram at 1550nm
柴 泰純, 岡本 淳, 林 穂高, 小川 和久, 富田 章久, 高畠 武敏, 後藤 優太, 品田 聡, 和田 尚也, 電子情報通信学会技術研究報告 = IEICE technical report : 信学技報, 119, 230, 105, 108, 17 Oct. 2019
電子情報通信学会, Japanese

Improvement of noise separation accuracy in image reconstruction in virtual phase conjugation based optical tomography
永吉 颯太, 岡本 淳, 後藤 優太, 小川 和久, 富田 章久, 電子情報通信学会技術研究報告 = IEICE technical report : 信学技報, 118, 449, 71, 74, 19 Feb. 2019
電子情報通信学会, Japanese

Improvement of noise separation accuracy in image reconstruction in virtual phase conjugation based optical tomography
永吉 颯太, 岡本 淳, 後藤 優太, 小川 和久, 富田 章久, 映像情報メディア学会技術報告 = ITE technical report, 43, 5, 71, 74, Feb. 2019
映像情報メディア学会, Japanese

光の連続性を活用した量子誤り耐性向上手法　　　　　　　　　　　　　　　
福井浩介, 藤井啓祐, 富田章久, 岡本淳, 日本物理学会誌, 74, 10, 720, 726, 2019
Japanese

Experiment on digital image multiplexing/demultiplexing using virtual phase conjugation for high density holographic memory
後藤 優太, 岡本 淳, 小川 和久, 富田 章久, 電子情報通信学会技術研究報告 = IEICE technical report : 信学技報, 117, 432, 261, 265, 15 Feb. 2018
電子情報通信学会, Japanese

Experiment on digital image multiplexing/demultiplexing using virtual phase conjugation for high density holographic memory
後藤 優太, 岡本 淳, 小川 和久, 富田 章久, 電子情報通信学会技術研究報告 = IEICE technical report : 信学技報, 117, 431, 261, 265, 15 Feb. 2018
電子情報通信学会, Japanese

Experiment on digital image multiplexing/demultiplexing using virtual phase conjugation for high density holographic memory
後藤 優太, 岡本 淳, 小川 和久, 富田 章久, 映像情報メディア学会技術報告 = ITE technical report, 42, 4, 261, 265, Feb. 2018
映像情報メディア学会, Japanese

Experiment on selective mode conversion using dual-phase modulation
前田 智弘, 岡本 淳, 小川 和久, 富田 章久, 若山 雄太, 釣谷 剛宏, 電子情報通信学会技術研究報告 = IEICE technical report : 信学技報, 117, 196, 51, 55, 31 Aug. 2017
電子情報通信学会, Japanese

Separation Characteristics of Volume Holographic Spatial Mode Demultiplexer at 850 nm Wavelength
清水 新平, 岡本 淳, 水川 郁弥, 小川 和久, 富田 章久, 高畠 武敏, 品田 聡, 和田 尚也, 電子情報通信学会技術研究報告 = IEICE technical report : 信学技報, 117, 196, 45, 50, 31 Aug. 2017
電子情報通信学会, Japanese

Experiment on Virtual Shift Method for Alignment Error Reduction of Holographic Diversity Interferometry
山岸 信博, 岡本 淳, 野澤 仁, 後藤 優太, 小川 和久, 富田 章久, 電子情報通信学会技術研究報告 = IEICE technical report : 信学技報, 116, 464, 153, 156, 20 Feb. 2017
電子情報通信学会, Japanese

Characterization of multiplexing technique using virtual phase conjugation for high density holographic memory
後藤 優太, 岡本 淳, 小川 和久, 富田 章久, 電子情報通信学会技術研究報告 = IEICE technical report : 信学技報, 116, 463, 147, 152, 20 Feb. 2017
電子情報通信学会, Japanese

Experiment on Dual-Wavelength Method toward Spatial Mode De-Multiplexing with Volume Hologram in Optical Communication Wavelength Band
清水 新平, 岡本 淳, 水川 郁弥, 小川 和久, 富田 章久, 高畠 武敏, 品田 聡, 和田 尚也, 電子情報通信学会技術研究報告 = IEICE technical report : 信学技報, 116, 463, 163, 168, 20 Feb. 2017
電子情報通信学会, Japanese

Experiment on Dual-Wavelength Method toward Spatial Mode De-Multiplexing with Volume Hologram in Optical Communication Wavelength Band
清水 新平, 岡本 淳, 水川 郁弥, 小川 和久, 富田 章久, 高畠 武敏, 品田 聡, 和田 尚也, 映像情報メディア学会技術報告 = ITE technical report, 41, 5, 163, 168, Feb. 2017
映像情報メディア学会, Japanese

Experiment on Virtual Shift Method for Alignment Error Reduction of Holographic Diversity Interferometry
山岸 信博, 岡本 淳, 野澤 仁, 後藤 優太, 小川 和久, 富田 章久, 映像情報メディア学会技術報告 = ITE technical report, 41, 5, 153, 156, Feb. 2017
映像情報メディア学会, Japanese

Characterization of multiplexing technique using virtual phase conjugation for high density holographic memory
後藤 優太, 岡本 淳, 小川 和久, 富田 章久, 映像情報メディア学会技術報告 = ITE technical report, 41, 5, 147, 152, Feb. 2017
映像情報メディア学会, Japanese

Basic Operation Simulation of Novel 3D Display Based on High-speed Analysis Method for Volume Hologram
舟越 久敏, 岡本 淳, 渋川 敦史, 電子情報通信学会技術研究報告 = IEICE technical report : 信学技報, 115, 458, 309, 313, 22 Feb. 2016
電子情報通信学会, Japanese

Virtual interferogram-generation algorithm for high-accurate phase measurement using only two holograms
野澤 仁, 岡本 淳, 小川 和久, 富田 章久, 映像情報メディア学会技術報告 = ITE technical report, 40, 6, 303, 307, Feb. 2016
映像情報メディア学会, Japanese

C-3-34 Complex-amplitude Control Using Lens-less Type Spatial Cross Modulation Method
Kan Yuta, Okamoto Atsushi, Shibukawa Atsushi, Funakoshi Hisatoshi, Sakuma Hiroki, Tomita Akihisa, Proceedings of the Society Conference of IEICE, 2015, 1, 108, 108, 25 Aug. 2015
The Institute of Electronics, Information and Communication Engineers, Japanese

B-10-33 Reduction of Modal Crosstalk using Random Diffuser for Spatial Mode Conversion with Spatial Light Modulator
Ishii Koki, Okamoto Atsushi, Tsuritani Takehiro, Wakayama Yuta, Goto Yuta, Tomita Akihisa, Proceedings of the Society Conference of IEICE, 2015, 2, 197, 197, 25 Aug. 2015
The Institute of Electronics, Information and Communication Engineers, Japanese

Dual GPU Acceleration of Compute Engine in Full Motion Simulator for Holographic Memory
舟越 久敏, 岡本 淳, 電子情報通信学会技術研究報告 = IEICE technical report : 信学技報, 114, 459, 27, 30, 23 Feb. 2015
電子情報通信学会, Japanese

EXPERIMENT ON THREE-DIMENSIONAL DISPLAY USING SPATIAL CROSS MODULATION METHOD WITH AN OPTICAL RANDOM DIFFUSER
H. Sakuma, A. Okamoto, A. Shibukawa, H. Funakoshi, Y. Goto, Y. Kan, A. Tomita, 2015 20TH MICROOPTICS CONFERENCE (MOC), 9386, 2015
We performed an experiment on a three-dimensional ( 3D) display using the spatial cross modulation (SCM) method with a single phase-only spatial light modulator and an optical random diffuser. The experimental result revealed the SCM has great potential to realize the 3D display with unprecedented high resolution and light utilization efficiency., IEEE, English

Dynamic wavefront compensation of signal beam in optical satellite communication system using phase conjugation technique
NISHIMAKI Kaori, OKAMOTO Atsushi, SHIBUKAWA Atsushi, TOMITA Akihisa, TAKAYAMA Yoshihisa, IEICE technical report. Circuits and systems, 114, 122, 87, 92, 09 Jul. 2014
We propose an optical satellite communication system which can dynamically compensate the signal beam wavefront using phase conjugation technique. The proposed system converts the signal beam wavefront into the phase conjugate wavefront using the double phase conjugate mirror formed by the photorefractive materials and communication beams. By using the time reversal wave and wavefront compensation effect produced by the phase conjugate wavefront, the automatic tracking of satellites and the background light reduction can be achieved at the same time. In addition, we consider the application of proposed method for the visible light communication on the ground., The Institute of Electronics, Information and Communication Engineers, English

B-10-58 Conversion and Extraction of Spatial Modes in a Multi-mode Fiber using Progressive Phase Conjugation Technique
Hirasaki Yuki, Okamoto Atsushi, Tomita Akihisa, Maeda Tomohiro, Proceedings of the IEICE General Conference, 2014, 2, 426, 426, 04 Mar. 2014
The Institute of Electronics, Information and Communication Engineers, Japanese

B-10-61 Reconfigurable Spatial Mode Conversion using a Spatial Light Modulator
Okamoto Atsushi, Hirasaki Yuki, Maeda Tomohiro, Zhao Yanfeng, Tomita Akihisa, Proceedings of the IEICE General Conference, 2014, 2, 429, 429, 04 Mar. 2014
The Institute of Electronics, Information and Communication Engineers, English

Readout Properties of Single Recorded Hologram in Self-Referential Holographic Data Storage
TAKABAYASHI Masanori, ETO Taisuke, BUNSEN Masatoshi, OKAMOTO Atsushi, OKAMOTO Takashi, IEICE technical report. Magnetic recording, 113, 267, 11, 16, 24 Oct. 2013
We describe the procedures, principles and properties of self-referential holography (SRH) in which any reference beam is not required to record and readout holograms.To improve the readout quality of SRH, we performed the numerical simulations and investigated the recording and readout properties in detail. As a results, we could successfully achieve the drastically improvement of the readout quality by shifting the focal position and by using oversampled additional pattern., The Institute of Electronics, Information and Communication Engineers, Japanese

Performance evaluation of hologram recording/retrieving with phase-shift embedded SQAM datapages
Umetsu Shuuhei, Bunsen Masatoshi, Takabayashi Masanori, Okamoto Atsushi, Proceedings of the Society Conference of IEICE, 2013, 1, 195, 195, 03 Sep. 2013
The Institute of Electronics, Information and Communication Engineers, Japanese

Recording and Reconstruction of 38-Level Spatial Quadrature-Amplitude Modulation Signal in Double-Referential Holographic Memory
ZUKERAN Keisuke, OKAMOTO Atsushi, TAKABAYASHI Masanori, SHIBUKAWA Atsushi, TOMITA Akihisa, ITE Technical Report, 37, 10, 1, 7, 15 Feb. 2013
We propose a double-referential holographic memory (DRHM) that can detect phase modulation signal by just entering reference beam into recording medium without additional system for generation and irradiation of the beam to interfere with signal beam. In this technique, by highly-accurate and simplified complex amplitude detection, high multi-level phase modulation signal and spatial quadrature-amplitude modulation (SQAM) signal become available, so it is expected that storage capacity and data transfer rate are greatly increased. In this paper, we describe the basic operation of the DRHM and evaluate multiple recording/reconstruction characteristics by numerical simulation. Besides, the method for furthermore improving reconstruction quality is newly proposed and its effectiveness is demonstrated., The Institute of Image Information and Television Engineers, Japanese

Improvement of Success Probability by Repeated Measurements in Entanglement Generation by Communication using Squeezed Light
松岡 史晃, 富田 章久, 岡本 淳, 量子情報技術研究会資料, 27, 73, 78, 27 Nov. 2012
量子情報技術時限研究専門委員会, Japanese

A Protocol of the Quantum Relay Using Quantum Group Secret Sharing and Distributed Computing
鈴木 貴士, 富田 章久, 岡本 淳, 量子情報技術研究会資料, 27, 16, 18, 27 Nov. 2012
量子情報技術時限研究専門委員会, English

2重位相共役鏡を用いた光衛星間通信システムにおける2値位相板による背景光低減手法
西牧可織, 岡本淳, 富田章久, 若山雄太, 高山佳久, 電気・情報関係学会北海道支部連合大会講演論文集(CD-ROM), 2012, ROMBUNNO.24, 20 Oct. 2012
Japanese

A-7-12 Quantum relay method using group secret sharing with quantum states
Suzuki Takashi, Tomita Akihisa, Okamoto Atushi, Proceedings of the IEICE General Conference, 2012, 180, 180, 06 Mar. 2012
The Institute of Electronics, Information and Communication Engineers, Japanese

Acquisition and tracking in inter-satellite communication with dynamically reconfigurable optical device(JC-SAT 2011)
Nishimaki Kaori, Okamoto Atsushi, Wakayama Yuta, Tomita Akihisa, Takayama Yoshihisa, Technical report of IEICE. SAT, 111, 336, 137, 140, 05 Dec. 2011
We propose an innovative acquisition and tracking system using a dynamically reconfigurable optical device for optical inter-satellite communication without growing in size and complications due to directivity control of laser beams. The proposed system provides relaxation of acquisition accuracy and suppression of beam divergence by utilization of phase conjugation to form an inter-satellite communication link. This paper reports on the temporal and spatial characteristics of our system for various incident beam angles to consider relaxation of acquisition accuracy and tracking speed., The Institute of Electronics, Information and Communication Engineers, English

BCI-1-7 Spatial mode excitation and separation for mode division multiplexing technology
Okamoto Atsushi, Soma Daiki, Oda Takuya, Tomita Akihisa, Wakayama Yuta, Proceedings of the Society Conference of IEICE, 2011, 1, "SS, 39"-"SS-40", 30 Aug. 2011
The Institute of Electronics, Information and Communication Engineers, Japanese

B-10-34 Holographic wavelength filter with ultra-broad tuning range for reconfigurable optical add-drop multiplexer
Wakayama Yuta, Okamoto Atsushi, Tomita Akihisa, Proceedings of the Society Conference of IEICE, 2011, 2, 247, 247, 30 Aug. 2011
The Institute of Electronics, Information and Communication Engineers, Japanese

B-10-35 Recording and Reconstruction of LP Modes in Volume Holographic Mode Multiplexer
Aoki Kohei, Okamoto Atsushi, Tomita Akihisa, Honma Satoshi, Proceedings of the Society Conference of IEICE, 2011, 2, 248, 248, 30 Aug. 2011
The Institute of Electronics, Information and Communication Engineers, Japanese

B-10-36 Experiment on LP Modes Excitation with Multi-mode Fiber for Mode Division Multiplex Communication
Soma Daiki, Okamoto Atsushi, Oda Takuya, Tomita Akihisa, Sato Kunihiro, Proceedings of the Society Conference of IEICE, 2011, 2, 249, 249, 30 Aug. 2011
The Institute of Electronics, Information and Communication Engineers, Japanese

Analysis of LP Mode Separation on All-optical Demultiplexer with Dynamic Multiple Holograms for Mode Division Multiplexing Communication
ODA Takuya, OKAMOTO Atsushi, SOMA Daiki, TOMITA Akihisa, Technical report of IEICE. LQE, 111, 186, 75, 80, 18 Aug. 2011
This study aims at the realization of mode division multiplexing (MDM) communication using multi-mode fiber by all-optical mode demultiplexer consisted of the dynamic multiple holograms. In this paper, we consider the separation of three multiplexed MDM signals, and investigate a mode separation characteristic for six combinations composed of three LP modes. In addition, to improve the separation performance of the all-optical mode demultiplexer, we clarify the dependence of the mode separation on the intensity ratio by varying of the two light intensities used in the hologram recording. Moreover, we show that the signal-to-noise ratio is greatly improved by choosing the combination of LP modes and intensity ratio adequately., The Institute of Electronics, Information and Communication Engineers, Japanese

B-10-98 Ultra-broad tuning range of reconfigurable optical add-drop multiplexer using dynamic holographic diffraction grating
Wakayama Yuta, Okamoto Atsushi, Tomita Akihisa, Proceedings of the IEICE General Conference, 2011, 2, 407, 407, 28 Feb. 2011
The Institute of Electronics, Information and Communication Engineers, Japanese

B-10-58 Experiment on Separating of LP Modes with Dynamic Multiplex Holographic Element for Mode Division Multiplex Communication
Soma Daiki, Okamoto Atsushi, Oda Takuya, Tomita Akihisa, Proceedings of the IEICE General Conference, 2011, 2, 367, 367, 28 Feb. 2011
The Institute of Electronics, Information and Communication Engineers, Japanese

Strongly confined light in a singe mode near quantum dots embedded in photonic crystals
Hiroyuki Nihei, Atsushi Okamoto, Proceedings of the International Conference on Numerical Simulation of Optoelectronic Devices, NUSOD, 139, 140, 2011
The strong confinement of light composed of a single localized mode inside photonic crystals can be achieved by coherent control, which is useful for keeping and processing quantum information. © 2011 IEEE., English

Apodization along thickness direction of holographic transmission grating in Sb-doped Sn2P2S6
Y. Wakayama, A. Okamoto, A. Tomita, A. A. Grabar, K. Sato, H. Nihei, Proceedings of the International Conference on Numerical Simulation of Optoelectronic Devices, NUSOD, 41, 42, 2011
This report demonstrates a grating apodization method along the thickness direction in a real-time holographic medium for maximizing the diffraction efficiency. Dynamic photo-induced index modulation is examined by the finite-difference beam-propagation method. © 2011 IEEE., English

Double‐Referential Collinear Holographic Memory and Spatial Quadrature Amplitude Modulation　　　　　　　　　　　　　　　
Technical Digest of The Joint International Symposium on Optical Memory and Optical Data Storage 2011 (ISOM/ODS’11), OTuD12, 2011

Holographic Diversity Detection of Spatial Quadrature Amplitude Modulation Signal for Dual‐Stage Holographic Memory　　　　　　　　　　　　　　　
Technical Digest of The Joint International Symposium on Optical Memory and Optical Data Storage 2011 (ISOM/ODS’11), OMB3, 2011

Evaluation of the Performance in Multilayer Collinear Holographic Memory with Movable Random Phase Mask　　　　　　　　　　　　　　　
Technical Digest of The Joint International Symposium on Optical Memory and Optical Data Storage 2011 (ISOM/ODS’11), OMD16, 2011

Self‐Referential Holographic Data Storage by Phase‐Modulation Technique　　　　　　　　　　　　　　　
Technical Digest of The Joint International Symposium on Optical Memory and Optical Data Storage 2011 (ISOM/ODS’11), OMB4, 2011

High‐Speed Full Motion Analysis Based on FFT-BPM for Collinear Holographic Memory　　　　　　　　　　　　　　　
Technical Digest of The Joint International Symposium on Optical Memory and Optical Data Storage 2011 (ISOM/ODS’11), OMD22, 2011

B-10-52 Experiment on All-optical Demultiplexer for Mode Division Multiplex Communication Technique
Oda Takuya, Okamoto Atsushi, Morita Kazuyuki, Proceedings of the IEICE General Conference, 2010, 2, 390, 390, 02 Mar. 2010
The Institute of Electronics, Information and Communication Engineers, Japanese

BI-8-2 High Performance Intersatellite Communication based on Double Phase Conjugation Technology
Okamoto Atsushi, Fujita Tomohiro, Wakayama Yuta, Takayama Yoshihisa, Proceedings of the IEICE General Conference, 2010, 1, "SS, 87"-"SS-88", 02 Mar. 2010
The Institute of Electronics, Information and Communication Engineers, Japanese

All-optical Demultiplexer for mode division multiplex communication technique with a multimode optical fiber
OKAMOTO ATSUSHI, ODA TAKUYA, MORITA KAZUYUKI, Tech Dig Int Conf Opt photonics Des Fabr, 7th, 169, 170, 2010, [Peer-reviewed]
English

Spatial Arrangement of Speckle-multiplexed Holograms using Directional Control of Shift Selectivity with Holographic Diffuser
Shuji Takahashi, Masatoshi Bunsen, Hirosuke Furuta, Atsushi Okamoto, TENCON 2010: 2010 IEEE REGION 10 CONFERENCE, 1625, 1628, 2010
We propose a method for directional control of the shift selectivity of the speckle-multiplexed holograms using the holographic diffuser whose surface profile varies with the orthogonal direction. The method improves the tolerance of the spatial multiplexed holograms for the repositioning error in the holographic storage. In addition, we utilize the nature that the shift selectivity in the propagation direction of the reference beam is intrinsically relaxed, and experimentally implement the spatial arrangement of the multiplexed holograms in both the "controlled" and the "intrinsically relaxed" directions. We show that the high quality output is obtained using our method by the measurement of the BER of the data-pages that are retrieved from the spatially arranged multiple holograms., IEEE, English

Spatial Quadrature Amplitude Modulation Method by Dual-Stage Holographic Memory
OKAMOTO A., International Workshop on Holographic Memories and Display 2010, Nov., 49, 50, 2010

Dual-Stage Holographic Memory based on Optical Recording and Digital Readout Technique　　　　　　　　　　　　　　　
Technical Digest of MOC 2010(CD-ROM), WP62, 2010

Experiment on Separating of LP modes by Dynamic Multiplex Holographic Element for Mode Division Multiplex Communication
SOMA D., MOC'10, Hsinchu, Taiwan, Oct., WB2, 2010

High Performance Intersatellite Communication Based on Background Light Reduction Technique with Double Phase Conjugate Mirror　　　　　　　　　　　　　　　
Technical Digest of MOC 2010(CD-ROM), WP44, 2010

Experiment on Photorefractive Collinear Holographic Data Storage by Semicircular Phase-Shift Methods　　　　　　　　　　　　　　　
Technical Digest of IWHM&D 2010, 53, 2010

Low Inter-page Crosstalk Recording by Multi-layer Collinear Holographic Memory　　　　　　　　　　　　　　　
Technical Digest of ISOM 2010(CD-ROM), Th-N-03, 2010

Symbol Error Rate Characteristics of Hybrid-Modulated Holographic Data Storage with Multi-Phase and 2/4 Intensity Modulation Code　　　　　　　　　　　　　　　
Technical Digest of ISOM 2010(CD-ROM), Th-N-02, 2010

Demonstration of Optical Threshold Secret Sharing Scheme with Secure Holographic Memory and Mutually Pumped Phase Conjugator　　　　　　　　　　　　　　　
Technical Digest of ISOM 2010(CD-ROM), Mo-E-03, 2010

Full Motion Analysis for Holographic Memory by Three-Dimensional Fast Fourier Transform Beam-Propagation Method　　　　　　　　　　　　　　　
Technical Digest of ISOM 2010(CD-ROM), Tu-I-14, 2010

Low-loss Coherent of Light Confined Near a Defect in Photonic Crystal　　　　　　　　　　　　　　　
Technical Digest of ISOM 2010(CD-ROM), Mo-B-04, 2010

Targeted optical control of confined light inside photonic crystals　　　　　　　　　　　　　　　
The proceedings of the Fourth International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (Metamaterials 2010), 16, 2010

Photorefractive Collinear Holographic Data Storage by Phase Shift Recording　　　　　　　　　　　　　　　
Fourth International Conference on Optical, Optelectronic and Photonic Materials and Applications (ICOOPMA 2010), A-0082, 2010

All-Optical Reconfigurable Add-Drop Multiplexer with Photorefractive Sn2P2S6:Sb Crystal　　　　　　　　　　　　　　　
Fourth International Conference on Optical, Optelectronic and Photonic Materials and Applications (ICOOPMA 2010), A-0080, 2010

Experiment on Dynamic Reconfigurable Diffraction Element for Mode Division Multiplex Communication
A. Okamoto, D. Soma, Y. Wakayama, A. Tomita, K. Sato, A. A. Grabar, 2010 15TH OPTOELECTRONICS AND COMMUNICATIONS CONFERENCE (OECC), 302, +, 2010
Light speed mode de-multiplexing is demonstrated by 3-dimentional phase matching for multiple spatial modes through holographic multiplexing technique. Separating of around 60-70% was achieved in experiments of separating multiplexed three modes by dynamic reconfigurable diffraction., IEICE-INST ELECTRONICS INFORMATION & COMMUNICATION ENGINEERS, English

Improvement of Diffraction Efficiency for All-Optical Tunable Wavelength Filter by Apodized Photorefractive Grating
Y. Wakayama, A. Okamoto, A. Tomita, H. Nihei, S. Honma, K. Suzuki, 2010 15TH OPTOELECTRONICS AND COMMUNICATIONS CONFERENCE (OECC), 692, +, 2010
A great improvement of diffraction efficiency in all-optical tunable holographic wavelength filters is shown by activating four corners of the material with photorefractive apodization method by optimizing the intensity ratio of the writing beams., IEICE-INST ELECTRONICS INFORMATION & COMMUNICATION ENGINEERS, English

Compatibility to WDM of Volume Holographic Demultiplexer for Spatial Mode Division Multiplexing
K. Morita, A. Okamoto, A. Tomita, M. Takabayashi, M. Bunsen, 2010 15TH OPTOELECTRONICS AND COMMUNICATIONS CONFERENCE (OECC), 252, +, 2010
WDM signals can be transmitted through a spatial mode division system with a multi-mode fiber and a volume holographic demultiplexer. Separation-angle for 100 channels of WDM signal can be suppressed two degrees on the demultiplexer., IEICE-INST ELECTRONICS INFORMATION & COMMUNICATION ENGINEERS, English

Polarization Dependence of Double Phase Conjugate Mirror with Sn2P2S6:Sb 1.5% Crystals　　　　　　　　　　　　　　　
Abstract Book of the 10th Russia/CIS/Baltic/Japan Symposium on Ferroelectricity (RCBJSF-10), 193, 2010

Mode division multiplex communication technique based on dynamic volume hologram and phase conjugation
Atsushi Okamoto, Kazuyuki Morita, Yuta Wakayama, Junya Tanaka, Kunihiro Sato, MICRO-OPTICS 2010, 7716, 771627, 2010
We propose mode division multiplex communication technique that can split a specific spatial mode in light from a spatial mode multiplexed in an optical fiber by fusion of a phase conjugation technique with spatial filtering processing by multiplexed volume holograms and random diffusers. In mode division multiplexing, the optical signal outgoing from the multimode optical fiber is in a condition that optical information of plural spatial modes is overlapped, therefore it is difficult to de-multiplex electrically after light detection. Our technique enables to split it into each mode all optically and to compensate temporal modal shift dynamically. Mode de-multiplexing is realized by multiplexed holographic arithmetic device and phase matching of a wave surface for the spatial mode orthogonal to time. Therefore, if we use indices in conventional electronic processing, a very high-speed operation equivalent to that of 10-100PFLOPS can be realized without causing any delay in light information to be transmitted. Moreover, it can realize constructions of a system that can dynamically respond to temporal mode variations and distortions with fiber transmissions by using a photorefractive medium. Separating of around 60-70% was achieved in an experiment of separating three multiplexed spatial modes by controlling a volume type dynamic reconfigurable device based on LiNbO3. It was clarified that the separation performance improved by an appropriate random phase mask in the numerical analysis., SPIE-INT SOC OPTICAL ENGINEERING, English

All-optical Demultiplexer for mode division multiplex communication technique with a multimode optical fiber　　　　　　　　　　　　　　　
Technical Digest of 7th International Conference on Optics-photonics Design & Fabrication (ODF’10), 20PSa-57, 2010

Polarization Alignment Free Interconnection by Dynamically Reconfigurable Double Phase Conjugation　　　　　　　　　　　　　　　
Technical Digest of 7th International Conference on Optics-photonics Design & Fabrication (ODF’10), 20S3-05, 2010

C-3-13 Dynamically Reconfigurable Optical Interconnection by Polarization-independent Mutually Pumped Phase-conjugate Mirror
Wakayama Yuta, Okamoto Atsushi, Grabar Alexander A, Proceedings of the Society Conference of IEICE, 2009, 1, 168, 168, 01 Sep. 2009
The Institute of Electronics, Information and Communication Engineers, Japanese

Development of Image-Based Simulation for Holographic Data Storage System by Fast Fourier Transform Beam-Propagation Method
Junya Tanaka, Atsushi Okamoto, Motoki Kitano, JAPANESE JOURNAL OF APPLIED PHYSICS, 48, 3, 03A028, Mar. 2009
We apply the fast Fourier transform beam-propagation method (FFT-BPM) to analyze holographic data storage systems (HDSSs), and develop an image-based simulation for diffraction characteristics in a transmission-type HDSS. The FFT-BPM is known as a very effective method for the design of large waveguides. By applying this method, we can obtain a beam profile in a recording medium that consists of a three-dimensional (3D) complex refractive-index distribution, and analyze the diffraction characteristics in page-oriented multiplexing holograms for an analytic region more practical than that required for the finite-difference time-domain (FDTD) method because of much lower computation time and memory. In this study, we demonstrate angular multiplexing by recording three data pages at different angles and visualize angular selectivity for diffraction efficiency and the sharpness of reconstructed images by a 3D numerical simulation. 2009 The Japan Society of Applied Physics DOI: 10.1143/JJAP.48.03A028, JAPAN SOCIETY APPLIED PHYSICS, English

Time-Domain Differential Detection of Phase-Modulated Signals for Phase-Only Holographic Data Storage
Masanori Takabayashi, Atsushi Okamoto, Kunihiro Sato, JAPANESE JOURNAL OF APPLIED PHYSICS, 48, 3, 03A032, Mar. 2009
Holographic data storage with phase-modulated signals has great advantages over conventional intensity-based memory. These include the efficient use of material dynamic range and light power in a spatial light modulator. On the other hand, phase-based holographic data storage has a disadvantage, which is the difficulty in distinguishing phase-modulated signals. We propose and demonstrate a new phase-modulated signal detection method with photorefractive two-wave mixing. This method has several advantages such as high energy efficiency, detection of multi valued phase-modulated signals, and alignment-free optics. In this study, we investigate the spatial resolution of the phase-modulated signal detection method and obtain a spatial resolution of 300-500 mu m of incident pixels. (C) 2009 The Japan Society of Applied Physics DOI: 10.1143/JJAP.48.03A032, JAPAN SOCIETY APPLIED PHYSICS, English

Security Assessment of Two-Wave Encryption
Motoki Kitano, Atsushi Okamoto, Takayuki Sano, JAPANESE JOURNAL OF APPLIED PHYSICS, 48, 3, 03A036, Mar. 2009
To determine the degree of security in two-wave encryption under practical conditions, we present a novel numerical technique for simulating the recording and readout of two-wave encryption. The calculation results of the retrieval characteristics show that the diffraction efficiency in an incorrect decryption is 10 times as low as that in correct decryption key and that the output data with an incorrect key is a white noise image. We estimate the necessary key correlation to decrypt an encrypted data is 0.2 when the length of an encryption key is 2313. This means that the decoding probability of the encryption key in two-wave encryption is less than 10(-6) even if such a short key is used. (C) 2009 The Japan Society of Applied Physics DOI: 10.1143/JJAP.48.03A036, JAPAN SOCIETY APPLIED PHYSICS, English

Nanophotonic quantum dot embedded in photonic crystals using a coherent control with a high spectrum resolution
Fumiaki Matsuoka, Hiroyuki Nihei, Atsushi Okamoto, PHOTONIC AND PHONONIC CRYSTAL MATERIALS AND DEVICES IX, 7223, 72231F.1-72231F.8, 2009
We demonstrate that the emission spectrum from a quantum dot near the edge of a photonic band gap (PBG) can be spectrally resolved on the subwavelength scale using coherent control. In the case of the coherent control, confined light near a quantum dot embedded in photonic crystals can be released by changing the phase of the external laser phase, without closing the PBG. Moreover, in this demonstration, we examine the spectrum resolution of the coherent control, which indicates that the spectrum resolution is the subwavelength scale. Therefore, even if there are many quantum dots are embedded in photonic crystals, we can be operated a quantum dot with a specific resonant frequency. This technique may provide a basis for N-qubit operation for quantum computations and nanophotonic devices., SPIE-INT SOC OPTICAL ENGINEERING, English

Photorefractive Time-Domain Differential Detection Method for High-Precision Distinction of Phase-Modulated Signals in Holographic Data Storage
Masanori Takabayashi, Atsushi Okamoto, ADVANCED OPTICAL CONCEPTS IN QUANTUM COMPUTING, MEMORY, AND COMMUNICATION II, 7225, 72250G.1-72250G.8, 2009
We develop a photorefractive time-domain differential detection (PR-TDDD) method in holographic data storage systems with considering the temporal response of photorefractive two-wave mixing (PR-TWM). Optimizing the parameters of PR-TDDD method provides high-precision distinction of phase-modulated signals, i.e. distinction of small phase difference. In PR-TDDD method, the phase information can be sequentially-distinguished by monitoring the output intensity of PR-TWM. This is because the output intensity of PR-TWM is changed when the signal phase is changed. In addition, the changing rate of the output intensity corresponds to that of the signal phase. The advantages of our method are high energy efficiency, alignment-free optics and the distinction of multi-valued phase-modulated signals. Especially, we focus attention on applying to phase-based holographic data storage systems, which can achieve homogeneous intensity distribution on recording plane, i.e. Fourier transform plane, in general, and high energy efficiency because of 100% white rate. More noteworthy is that multi-valued phase-based holographic data storage can be realized by using PR-TDDD method. In this work, we consider the important parameters in PR-TDDD method; signal-to-pump beam intensity ratio, photorefractive coupling strength, and photorefractive time constant. The balance between these parameters is important for realizing the high-precision distinction of phase-modulated signal., SPIE-INT SOC OPTICAL ENGINEERING, English

Shift selectivity in multi-layered collinear holographic system by medium shift along the thickness direction　　　　　　　　　　　　　　　
Technical Digest of IWHM&D 2009, 13, 14, 2009

Fundamental Experiment on Rewritable Collinear Holographic Data Storage　　　　　　　　　　　　　　　
Technical Digest of IWHM&D 2009, 35, 36, 2009

Dynamically reconfigurable optical device with nanoscale dynamic self-organization in Sn2P2S6 crystal　　　　　　　　　　　　　　　
Technical Digest of the 7th Asia-Pacific Conference on Near-Field Optics (APNFO-7), 127, 2009

Spectrum resolution of a coherent control of Er3+ ions embedded in inverse opal structure　　　　　　　　　　　　　　　
Technical Digest of the 7th Asia-Pacific Conference on Near-Field Optics (APNFO-7), 128, 2009

Apodization method by nonuniform spatial distribution of diffraction gratings for photorefractive wavelength filter　　　　　　　　　　　　　　　
Asia Communications and Photonics Conference and Exhibition (ACP 2009), WL15, 2009

Volume Holographic Demultiplexer for Spatial Mode Division Multiplexing in Optical Fiber Communication　　　　　　　　　　　　　　　
Asia Communications and Photonics Conference and Exhibition (ACP 2009), WL16, 2009

Spatial Filtering System on Optical Intersatellite Communication with Double Phase Conjugate Mirror　　　　　　　　　　　　　　　
Asia Communications and Photonics Conference and Exhibition (ACP 2009), WL54, 2009

Coherent Control of Targeted Quantum Dot in Photonic Crystals for Nanophotonics Devices　　　　　　　　　　　　　　　
Asia Communications and Photonics Conference and Exhibition (ACP2009), FQ2, 2009

Dynamically reconfigurable fiber coupling by polarization-independent double phase-conjugation　　　　　　　　　　　　　　　
Technical Digest of MOC 2009, 272, 273, 2009

Directional control of shift selectivity of speckle-multiplexed holograms for improving repositioning tolerance　　　　　　　　　　　　　　　
Technical Digest of ISOM 2009, Tu-G-18, 2009

Reproducing evaluations of optical threshold secret sharing technique based on two-wave encryption　　　　　　　　　　　　　　　
Technical Digest of ISOM 2009, Tu-G-33, 2009

Phase-oriented simulation for shift-multiplexed holographic data storage system by fast-Fourier transform beam-propagation method　　　　　　　　　　　　　　　
Technical Digest of ISOM 2009, Tu-G-26, 2009

Phase-differential modulation for phase-based holographic data storage with photorefractive time-domain differential detection method　　　　　　　　　　　　　　　
Technical Digest of ISOM 2009, Tu-G-32, 2009

High Speed Phase Detection for Holographic Data Storage by Photorefractive Time-Domain Differential Detection with Sb: Sn2P2S6 Crystal
M. Takabayashi, A. Okamoto, Y. Kojima, A. A. Grabar, PS: 2009 INTERNATIONAL CONFERENCE ON PHOTONICS IN SWITCHING, 174, +, 2009
We demonstrated photorefractive time-domain differential phase detection method with Sb: Sn2P2S6 (SPS) which has very fast response speed. SIPS crystal can improve the phase detection speed in holographic data storage than the other photorefractive material., IEEE, English

Optical interconnection for multi-wavelength signals with volume holographic router
Satoshi Honma, Sheng Baw Luog, Shinzo Muto, Atsushi Okamoto, 2009 14TH OPTOELECTRONICS AND COMMUNICATIONS CONFERENCE (OECC 2009), 442, +, 2009
We propose an optical interconnection for multi-wavelength signals with a volume holographic router. 100 wiring patterns for two wavelength signal are switched by 1mm range of movement of the router., IEEE, English

Targeted coherent control inside photonic band gaps for nanophotonics devices
Hiroyuki Nihei, Fumiaki Matsuoka, Atsushi Okamoto, 2009 14TH OPTOELECTRONICS AND COMMUNICATIONS CONFERENCE (OECC 2009), 616, +, 2009
We propose targeted coherent control of light confined near a quantum dot embedded in three-dimensional photonic crystals, which provides the basis of quantum information processing that can be used for nano-photonics devices., IEEE, English

Dynamically Reconfigurable Optical Waveguides with Sn2P2S6 Crystal for Free Space Optical Wiring
Kazutaka Hira, Atsushi Okamoto, Yasunori Kojima, Alexander A. Grabar, 2009 14TH OPTOELECTRONICS AND COMMUNICATIONS CONFERENCE (OECC 2009), 322, +, 2009
We demonstrated a dynamically reconfigurable optical waveguide based on a double phase conjugate mirror with a Sn2P2S6 crystal, which is applicable to future optical communication technologies such as three dimensional optical wiring and free space optics., IEEE, English

Spatial resolutions for applying photorefractive polymers to diffractive elements
Atsushi Okamoto, Kazuhiro Harasaka, Masatoshi Bunsen, Masanori Takabayashi, Shuji Rokutanda, JOURNAL OF MODERN OPTICS, 56, 12, 1323, 1334, 2009
Spatial resolutions of diffracted beams by photorefractive polymers are investigated in detail for applying the polymers to diffractive optical elements. The coupled wave equations for the four-wave mixing in photorefractive polymers and their solutions by applying the two-beam coupling approximation are derived taking the orientational enhancement effect into consideration. Characteristics of the diffraction efficiency of the polymers for the applied electric field, the incident angles of beams, the incident radiation intensity and the polarization are clarified. Furthermore, resolutions of diffracted images with the polymers are discussed by a numerical analysis from the viewpoint of the Bragg diffraction in a spatial frequency domain. An experiment with the TPD (tetra-phenyl-diphenyldiamine) acrylate based photorefractive polymers and the USAF test target is also performed to measure the spatial resolution of two-dimensional images diffracted by the polymer and to verify the calculated results. It is revealed that high resolution over 50 lp mm-1 can be obtained with sufficient diffraction efficiency in the case of the polymer thickness of several 10 mu m., TAYLOR & FRANCIS LTD, English

Link Budget Analysis for Optical Intersatellite Communication System with Double Phase Conjugate Mirror　　　　　　　　　　　　　　　
Proceedings of 1st International Conference on Space Optical Systems and Applications (ICSOS), 32, 2009

Nanophotonic quantum dot embedded in photonic crystals using a coherent control with a high spectrum resolution
Fumiaki Matsuoka, Hiroyuki Nihei, Atsushi Okamoto, PHOTONIC AND PHONONIC CRYSTAL MATERIALS AND DEVICES IX, 7223, 72231F1-72231F8, 2009
We demonstrate that the emission spectrum from a quantum dot near the edge of a photonic band gap (PBG) can be spectrally resolved on the subwavelength scale using coherent control. In the case of the coherent control, confined light near a quantum dot embedded in photonic crystals can be released by changing the phase of the external laser phase, without closing the PBG. Moreover, in this demonstration, we examine the spectrum resolution of the coherent control, which indicates that the spectrum resolution is the subwavelength scale. Therefore, even if there are many quantum dots are embedded in photonic crystals, we can be operated a quantum dot with a specific resonant frequency. This technique may provide a basis for N-qubit operation for quantum computations and nanophotonic devices., SPIE-INT SOC OPTICAL ENGINEERING, English

Photorefractive Splicing Device with Double Phase Conjugate Mirror Using Sn2P2S6:Sb Crystal
Yuta Wakayama, Atsushi Okamoto, Kohei Shimayabu, Yasunori Kojima, Alexander A. Grabar, OPTICAL COMPONENTS AND MATERIALS VI, 7212, 72120Q1-72120Q10, 2009
We develop a splicing device for photonic crystal fibers (PCFs) based on a double phase conjugate mirror (DPCM) using a novel photorefractive (PR) Sn2P2S6:Sb 1.5% crystal. This PR splicer has many attractive characteristics including modal field compensation and the automatic reconfiguration of the optical path. Utilizing a DPCM as the splicer, our device can adapt to misalignments automatically since the incident beams continuously rewrite an index grating which formed in the crystal. By the implementation of the Sn2P2S6:Sb crystal, the response time for the characteristic of dynamic reconfiguration is improved several-hundred-fold compared with conventional materials, e. g. BaTiO3. We demonstrate that the high angular tolerance is provided using the DPCM with the Sn2P2S6:Sb crystal. When the misalignment of the incident angle is from -7 degrees to 8 degrees, the increment of coupling loss is less than 0.6dB. This is several-ten-fold compared with the fusion splicing. We reveal the dependence of the coupling loss on the position of the incident beams and also the dependence of the energy flow on the propagation distance for the first time with the two-dimensional finite-difference beam-propagation method. Using our numerical simulation tool, we can visually investigate the beam propagation property considering the influence of the fanning effect in the Sn2P2S6 crystals., SPIE-INT SOC OPTICAL ENGINEERING, English

Photorefractive Time-Domain Differential Detection Method for High-Precision Distinction of Phase-Modulated Signals in Holographic Data Storage
Masanori Takabayashi, Atsushi Okamoto, ADVANCED OPTICAL CONCEPTS IN QUANTUM COMPUTING, MEMORY, AND COMMUNICATION II, 7225, 72250G1-72250G8, 2009
We develop a photorefractive time-domain differential detection (PR-TDDD) method in holographic data storage systems with considering the temporal response of photorefractive two-wave mixing (PR-TWM). Optimizing the parameters of PR-TDDD method provides high-precision distinction of phase-modulated signals, i.e. distinction of small phase difference. In PR-TDDD method, the phase information can be sequentially-distinguished by monitoring the output intensity of PR-TWM. This is because the output intensity of PR-TWM is changed when the signal phase is changed. In addition, the changing rate of the output intensity corresponds to that of the signal phase. The advantages of our method are high energy efficiency, alignment-free optics and the distinction of multi-valued phase-modulated signals. Especially, we focus attention on applying to phase-based holographic data storage systems, which can achieve homogeneous intensity distribution on recording plane, i.e. Fourier transform plane, in general, and high energy efficiency because of 100% white rate. More noteworthy is that multi-valued phase-based holographic data storage can be realized by using PR-TDDD method. In this work, we consider the important parameters in PR-TDDD method; signal-to-pump beam intensity ratio, photorefractive coupling strength, and photorefractive time constant. The balance between these parameters is important for realizing the high-precision distinction of phase-modulated signal., SPIE-INT SOC OPTICAL ENGINEERING, English

High sensitive and efficient photorefractive tunable optical wavelength filter with applied external field
Katsuhito Suzuki, Atsushi Okamoto, Masanori Takabayashi, Satoshi Honma, OPTICAL COMPONENTS AND MATERIALS VI, 7212, 72120W1-72120W9, 2009
We develop a tunable optical wavelength filter with PR (photorefractive) materials applied the external field for achieving higher sensitivity and efficiency. In the past, the diffraction efficiency of the PR tunable filters with transmission gratings has been much lower than other conventional wavelength filters, such as the array wavelength gratings filter, the thin film filter, and the fiber Bragg gratings filter. By applying the external field to PR materials, we can obtain the refractive index modulation depth of 13 times larger than that without applied field, specifically in lithium niobate with the acceptor density of similar to 10(22) [1/m(3)] and the voltage of 10 [kV/cm]. Our PR tunable filter provides reconfigurable wavelength routing of the signal beam since the various diffraction gratings can be immediately induced and multiplexed by changing incident conditions of two coherent writing beams viewpoint in comparing experimental results to numerical simulations, and can be rewritten dynamically through the PR effect. These advantages allow us to achieve more flexible optical net work based on the wavelength division multiplexing technique. In this work, we calculate the relationship between the diffraction efficiency and the magnitude of the applied external field by solving coupled wave equations in the case of lithium niobate, respectively., SPIE-INT SOC OPTICAL ENGINEERING, English

Experiments on Double Phase Conjugate Mirror with a Photorefractive Sb:Sn2P2S6 Crystal
Yasunori Kojima, Atsushi Okamoto, Alexander A. Grabar, Masanori Takabayashi, Kohei Shimayabu, FERROELECTRICS, 378, 121, 128, 2009
We present various optical basic properties of a 1.5% doped Sb:Sn2P2S6 crystal experimentally and demonstrate a double phase conjugate mirror (DPCM). We measured the reflection, absorption and scattering of this crystal. The large coupling strength L = 8.2 was obtained by the experiment of two-wave mixing. In addition, we succeeded in the formation of the DPCM and achieved the high diffraction efficiency of 42%. This crystal was suitable for DPCM applications of high speed response., TAYLOR & FRANCIS LTD, English

Coherent control of excited atomic states inside a three-dimensional photonic bandgap
Journal of Modern Optics, 55, 15, 2391, 2399, 10 Sep. 2008
English

Filtering property of all-optical tunable filter with photorefractive waveguide and suppression of cross-talk
TSUDA Naoya, HONMA Satoshi, MUTO Shinzo, OKAMOTO Atsushi, IEICE technical report, 108, 192, 133, 137, 28 Aug. 2008
Development of tunable optical filters has been expected for improvement of data transmission capacitance in optical communications. In this report, we propose a tunable frequency filter with a photorefractive (PR) waveguide. It is able to induce index gratings having arbitrary wavelength by radiation of low power interfering light in the PR materials. The PR waveguide is therefore promising device to be applied to optical filters and switches. We analyze the filtering property such as diffraction efficiency and bandwidth. We consider suppression method of channel crosstalk using PR two-wave mixing., The Institute of Electronics, Information and Communication Engineers, Japanese

Targeted Optical Control of an Active Medium Embedded In Photonic Crystals
Nihei Hiroyuki, Okamoto Atsushi, Jpn J Appl Phys, 47, 7, 5781, 5783, 25 Jul. 2008
We demonstrate optical control of an active medium, such as a quantum dot or an impurity atom, embedded in three-dimensional photonic crystals. The optical control provides a very high spectral selectivity, which allows us to control confined light near a targeted active medium with a specific resonant frequency. Using such an optical control, even if the other active mediums are embedded nearby, we may selectively control only the targeted active medium, leading to a basic operation of an optical memory on the nanoscale below the light wavelength., INSTITUTE OF PURE AND APPLIED PHYSICS

Targeted optical control of an active medium embedded in photonic crystals
Hiroyuki Nihei, Atsushi Okamoto, Japanese Journal of Applied Physics, 47, 7, 5781, 5783, 18 Jul. 2008
We demonstrate optical control of an active medium, such as a quantum dot or an impurity atom, embedded in three-dimensional photonic crystals. The optical control provides a very high spectral selectivity, which allows us to control confined light near a targeted active medium with a specific resonant frequency. Using such an optical control, even if the other active mediums are embedded nearby, we may selectively control only the targeted active medium, leading to a basic operation of an optical memory on the nanoscale below the light wavelength., English

Improved holographic recording techniques for data-page rewriting
Masatoshi Bunsen, Hirosuke Furuta, Kuniaki Aragane, Atsushi Okamoto, JAPANESE JOURNAL OF APPLIED PHYSICS, 47, 7, 5977, 5980, Jul. 2008
Novel holographic recording configurations capable of selective erasure of multiplexed holograms for data-page rewriting in holographic storage are presented. By using a half wave plate and a polarizing beam splitter as the phase control device of the interference pattern in holographic recording/erasure procedure, comparatively large-area and finespun data-pages may be recorded, selectively erased, and rewritten in simple operations. We experimentally demonstrate the selective erasure of multiplexed data-pages in photorefractive iron-doped LiNbO(3) crystals, and show the effectiveness of the configuration. We also propose a method to improve the in-plane uniformity of the erasure making use of the diffuser in the optical path of the object beam which is employed for dispersing the object image and the phase conjugate readout technique., JAPAN SOCIETY APPLIED PHYSICS, English

Improved holographic recording techniques for data-page rewriting
Masatoshi Bunsen, Hirosuke Furuta, Kuniaki Aragane, Atsushi Okamoto, JAPANESE JOURNAL OF APPLIED PHYSICS, 47, 7, 5977, 5980, Jul. 2008
Novel holographic recording configurations capable of selective erasure of multiplexed holograms for data-page rewriting in holographic storage are presented. By using a half wave plate and a polarizing beam splitter as the phase control device of the interference pattern in holographic recording/erasure procedure, comparatively large-area and finespun data-pages may be recorded, selectively erased, and rewritten in simple operations. We experimentally demonstrate the selective erasure of multiplexed data-pages in photorefractive iron-doped LiNbO(3) crystals, and show the effectiveness of the configuration. We also propose a method to improve the in-plane uniformity of the erasure making use of the diffuser in the optical path of the object beam which is employed for dispersing the object image and the phase conjugate readout technique., JAPAN SOCIETY APPLIED PHYSICS, English

Targeted optical control of an active medium embedded in photonic crystals
Hiroyuki Nihei, Atsushi Okamoto, JAPANESE JOURNAL OF APPLIED PHYSICS, 47, 7, 5781, 5783, Jul. 2008
We demonstrate optical control of an active medium, such as a quantum dot or an impurity atom, embedded in three-dimensional photonic crystals. The optical control provides a very high spectral selectivity, which allows us to control confined light near a targeted active medium with a specific resonant frequency. Using such an optical control, even if the other active mediums are embedded nearby, we may selectively control only the targeted active medium, leading to a basic operation of an optical memory on the nanoscale below the light wavelength., JAPAN SOCIETY APPLIED PHYSICS, English

Image cross-connector using a photorefractive polymer
Atsushi Okamoto, Kazuhiro Harasaka, Hidenobu Muranaka, Takayuki Sano, Akinori Nishio, JOURNAL OF MODERN OPTICS, 55, 2, 311, 322, 2008
We propose an image cross-connector using an organic photorefractive polymer. With this device, it is possible to perform a reconfigurable connection between multiple input-output image ports by setting the incident angle of individual control beams to minute levels. The use of a polymer can reduce the thickness of the index grating to be induced inside the medium, which can also reduce the distortion of the output image and bring about high precise image connection without an additional optical system. We conduct an experiment with a hole-transport polymer PATPD to verify the operations of an image cross-connector, in which different images from a vertical array of input images would be connected separately to two output ports by two control beams that were injected at different angles., TAYLOR & FRANCIS LTD, English

High-resolution coherent control of a quantum dot embedded in photonic crystals
Hiroyuki Nihei, Atsushi Okamoto, 2008 IEEE PHOTONICSGLOBAL@SINGAPORE (IPGC), VOLS 1 AND 2, 261, +, 2008
We present the coherent control with a high-resolution spectrum of a quantum dot embedded in photonic crystals, which can he used for nanophotonics devices in a subwavelength region., IEEE, English

Coherent control of excited atomic states inside a three-dimensional photonic bandgap
Hiroyuki Nihei, Atsushi Okamoto, JOURNAL OF MODERN OPTICS, 55, 15, 2391, 2399, 2008
We demonstrate the coherent control of the excited state of an atom embedded in three-dimensional photonic bandgap (3D PBG) structures. The coherent control allows us to obtain a long-lifetime Rabi oscillation or several types of steady-state inversion, depending on the laser phase, in which the relaxation of an excited atom is strongly suppressed. Such a coherent control suggests the possibility of extending the atomic system to a low loss quantum logic gate for optical quantum computation., TAYLOR & FRANCIS LTD, English

Optical Intersatellite Communication System with Double Phase Conjugate Mirror
Kohei Shimayabu, Atsushi Okamoto, Yoshihisa Takayama, Kunihiro Sato, Yusuke Nakayama, 2008 34TH EUROPEAN CONFERENCE ON OPTICAL COMMUNICATION (ECOC), P.4.05, 2008
Optical intersatellite communication system with double phase conjugate mirror is proposed. We experimentally demonstrate that double phase conjugate mirror can be performed as optical amplifier besides auto tracking., IEEE, English

Analysis of double phase-conjugate mirror using the FD-BPM
Y. Wakayama, Y. Nakayama, A. Okamoto, Y. Takayama, 2008 INTERNATIONAL CONFERENCE ON PHOTONICS IN SWITCHING, 114, +, 2008
We present a new optical fiber coupling device with doublle phase-conjugate mirror which corresponds to photonic crystal fiber. In our report, diffraction efficiency of the double phase-conjugate mirror is calculated using finite-difference beam propagation method., IEEE, English

Nano-photonic switching in a quantum dot embedded in photonic crystals
F. Matsuoka, H. Nihei, A. Okamoto, 2008 INTERNATIONAL CONFERENCE ON PHOTONICS IN SWITCHING, 94, +, 2008
We demonstrate that light near a targeted quantum dot embedded in photonic crystals can be strongly confined or completely released using pump laser pulses, which may provide a basic operation of nano-photonic switching., IEEE, English

Suppression of crosstalk by apodization of photorefractive transmission grating for wavelength filter
K. Suzuki, H. Yoshida, A. Okamoto, S. Honma, 2008 INTERNATIONAL CONFERENCE ON PHOTONICS IN SWITCHING, 88, +, 2008
We propose apodization of transmission grating for the wavelength filter controlled by writing beam intensity in photorefractive crystal. The interchannel crosstalk is suppressed by about 6dB compared with that without apodization., IEEE, English

Simulation technique for diffraction efficiency characteristics in holographic data storage system based on FFT-BPM　　　　　　　　　　　　　　　
Technical Digest of ISOM/ODS 2008, 87, 89, 2008

Numerical Simulation of Retrieving Characteristics in Holographic Data Storage by Two-Wave Encryption　　　　　　　　　　　　　　　
Technical Digest of ISOM/ODS 2008, 90, 92, 2008

Spatial Resolution of Phase-Modulated Signal Detection Method using Photorefractive Two-Wave Mixing for Holographic Data Storage System　　　　　　　　　　　　　　　
Technical Digest of ISOM/ODS 2008, 81, 83, 2008

Selective Erasure of Multiplexed Holograms Using Beam Amplification by Mutually Pumped Phase Conjugate Mirror　　　　　　　　　　　　　　　
Technical Digest of ISOM/ODS 2008, 78, 80, 2008

Nanophotonic Active Devices using Tunability of Photonic Band Gap　　　　　　　　　　　　　　　
ABSTRACT BOOK of Russia/CIS/Baltic/Japan symposium on Ferroelectricity (RCBJSF-9), 64, 64, 2008

Double Phase Conjugate Mirror in a Photorefractive Sb:Sn2P2S6 Crystal　　　　　　　　　　　　　　　
ABSTRACT BOOK of Russia/CIS/Baltic/Japan symposium on Ferroelectricity (RCBJSF-9), 165, 165, 2008

Image cross-connector using a photorefractive polymer
Atsushi Okamoto, Kazuhiro Harasaka, Hidenobu Muranaka, Takayuki Sano, Akinori Nishio, JOURNAL OF MODERN OPTICS, 55, 2, 311, 322, 2008
We propose an image cross-connector using an organic photorefractive polymer. With this device, it is possible to perform a reconfigurable connection between multiple input-output image ports by setting the incident angle of individual control beams to minute levels. The use of a polymer can reduce the thickness of the index grating to be induced inside the medium, which can also reduce the distortion of the output image and bring about high precise image connection without an additional optical system. We conduct an experiment with a hole-transport polymer PATPD to verify the operations of an image cross-connector, in which different images from a vertical array of input images would be connected separately to two output ports by two control beams that were injected at different angles., TAYLOR & FRANCIS LTD, English

Shift-phase code multiplexing technique for holographic memories and optical interconnection
Satoshi Honma, Shinzo Muto, Atsushi Okamoto, HOLOGRAPHY AND DIFFRACTIVE OPTICS III, 6832, 68322P, 2008
Holographic technologies for optical memories and interconnection devices have been studied actively because of high Storage capacity.. many wiring patterns and high transmission rate. Among multiplexing techniques such as angular, phase code and wavelength-multiplexing, speckle multiplexing technique have gotten attention due to the simple optical setup having an adjustable random phase filter in only one direction.
To keep simple construction and to suppress crosstalk among adjacent page data or wiring patterns for efficient ZD holographic memories and interconnection, we have to consider about optimum randomness of the phase filter. The high randomness causes expanding an illumination area of reference beam on holographic media. On the other hands, the small randomness causes the crosstalk between adjacent hologram data.
We have proposed the method of holographic multiplexing, shift-phase code multiplexing with a two-dimensional orthogonal matrix phase filter. A lot of orthogonal phase codes can be produced by shifting the phase filter in one direction. It is able to read and record the individual holograms with low crosstalk. We give the basic experimental result on holographic data multiplexing and consider the phase pattern of the filter to suppress the crosstalk between adjacent holograms sufficiently., SPIE-INT SOC OPTICAL ENGINEERING, English

Suppression of crosstalk by apodization of photorefractive transmission grating for wavelength filter
YOSHIDA Hirofimi, OKAMOTO Atsushi, HONMA Satoshi, IEICE technical report. EMD, 107, 196, 139, 143, 16 Aug. 2007
We propose the suppression method of the crosstalk by the apodization of photorefractive(PR) transmission gratings for wavelength filter. When two coherent writing beams illuminate a PR crystal, an index grating is induced by PR effect and the asymmetric energy transfer occurs. The crosstalk is suppressed by the apodization of the grating in a PR crystal. In this paper, we analyze the bandwidth of diffracted beam for the writing beam intensity. We also show the optimum writing beam intensity ratio for minimizing the crosstalk. Compared with the case that without apodization, the crosstalk is suppressed by about 4dB under a coupling strength of γL=6.0., The Institute of Electronics, Information and Communication Engineers, Japanese

High-speed replication system using photorefractive amplifier for holographic ROMs : Equalization of diffraction efficiency of copy holograms
TAKAHASHI Nobuhiro, OKAMOTO Atsushi, SANO Takayuki, ITO Terumasa, IEICE technical report. EMD, 107, 196, 133, 137, 16 Aug. 2007
In order to reduce the replication time of holographic ROMs, we propose a high-speed replication system using a photorefractive amplifier (PRA). Our system enables high-speed replication of holographic ROMs by amplification of rather weak beams diffracted from a master medium with a PRA. We show that our system allows high-speed replication of holographic ROMs, compared with the other copy systems. Our system has the problem that diffraction efficiency of copy holograms at each spot is not equal because gain given by a PRA depends on the incident beam angle. We can equalize diffraction efficiency of copy holograms by adjusting diffraction efficiency of master holograms., The Institute of Electronics, Information and Communication Engineers, Japanese

Recording schedule for partially coherent hologram multiplexing in a photorefractive medium
Applied Optics, 46, 23, 5902, 5911, 10 Aug. 2007
English

All-optical multifunctional logic gates for image information using photorefractive two-wave mixing
Daisuke Ishikawa, Atsushi Okamoto, Satoshi Honma, Terumasa Ito, Kohei Shimayabu, Kunihiro Sato, Optical Review, 14, 4, 246, 251, Jul. 2007
In this paper, we propose all-optical multifunctional logic gates for image information using photorefractive (PR) two-wave mixing. The optical setup is simply configured compared with the other all-optical logic gates for image information. The XOR-, OR-, and AND-operation are all-optically performed in the same optical setup through the transitional response of the PR medium. One can switch these logic operations simply by means of the on-off control of the signal and the pump beam illumination. We analyze the spatial distribution of beam intensity in these logic gates using a finite-difference beam propagation method (FD-BPM) and the crosstalk between adjoining pixels is examined from the result. We also experimentally verify that the XOR-, OR-, and AND-gates are realized in the same optical setup. © 2007 The Optical Society of Japan., English

Analysis of diffuser shift margin in spatial spread-spectrum holographic multiplexing
Terumasa Ito, Atsushi Okamoto, Kunihiro Sato, Optical Review, 14, 4, 219, 223, Jul. 2007
We present a novel numerical model for analyzing shift margin in spatial spread-spectrum (SSS) multiplexing, in which the spatial phase of signal beams, not in reference beams, is modulated and demodulated by a random diffuser to multiplex holograms. The shift margin is determined not by the Bragg effect of a thick hologram, but mainly by the phase correlation property of the diffuser used. In our model, we simulate signal data patterns and a smooth rough surface of a diffuser using oversampling and zero-padding, which allows us to cover crosstalk calculations and direct bit-errors calculations, with a fine shift resolution and a wide diffusion angle range. Calculation results revealed that the practical shift margin that ensures a signal to noise ratio more than 3.0 and a bit-error rate less than 10-2 is in the range of 0.3ωeff-0.5ωeff, where ωeff is the effective autocorrelation length of the diffuser transmission function. This model will be helpful in designing the optimum random diffuser profile for SSS multiplexing. © 2007 The Optical Society of Japan., English

Analysis of diffuser shift margin in spatial spread-spectrum holographic multiplexing
Terumasa Ito, Atsushi Okamoto, Kunihiro Sato, OPTICAL REVIEW, 14, 4, 219, 223, Jul. 2007
We present a novel numerical model for analyzing shift margin in spatial spread-spectrum (SSS) multiplexing, in which the spatial phase of signal beams, not in reference beams, is modulated and demodulated by a random diffuser to multiplex holograms. The shift margin is determined not by the Bragg effect of a thick hologram, but mainly by the phase correlation property of the diffuser used. In our model, we simulate signal data patterns and a smooth rough surface of a diffuser using oversampling and zero-padding, which allows LIS to cover crosstalk calculations and direct bit-errors calculations. with a fine shift resolution and a wide diffusion angle range. Calculation results revealed that the practical shift margin that ensures a signal to noise ratio more than 3.0 and a bit-error rate less than 10(-2) is in the range of 0.3 omega(eff)-0.5 omega(eff), where omega(eff) is the effective autocorrelation length of the diffuser transmission function. This model will be helpful in designing the optimum random diffuser profile for SSS multiplexing. (c) 2007 The Optical Society of Japan., OPTICAL SOC JAPAN, English

All-optical multifunctional logic gates for image information using Photorefractive two-wave mixing
Daisuke Ishikawa, Atsushi Okamoto, Satoshi Honma, Terumasa Ito, Kohei Shimayabu, Kunihiro Sat, OPTICAL REVIEW, 14, 4, 246, 251, Jul. 2007
In this paper, we propose all-optical multifunctional logic gates for image information using photorefractive (PR) two-wave mixing. The optical setup is simply configured compared with the other all-optical logic gates for image information. The XOR-, OR-, and AND-operation are all-optically performed in the same optical setup through the transitional response of the PR medium. One can switch these logic operations simply by means of the on-off control of the signal and the pump beam illumination. We analyze the spatial distribution of beam intensity in these logic gates using a finite-difference beam propagation method (FD-BPM) and the crosstalk between adjoining pixels is examined from the result. We also experimentally verify that the XOR-, OR-, and AND-gates are realized in the same optical setup. (c) 2007 The Optical Society of Japan., OPTICAL SOC JAPAN, English

Mutually pumped phase conjugate mirror using cross polarized photorefractive coupling
Atsushi Okamoto, Satoshi Honma, Shunsuke Uemura, Terumasa Ito, OPTICS AND LASER TECHNOLOGY, 39, 4, 881, 884, Jun. 2007
This paper presents a new proposal for a mutually pumped phase conjugate mirror (MPPCM) using cross polarization. In the cross polarized MPPCM, two light beams, whose polarizations are orthogonal to each other, incident on a photorefractive crystal, Causing photorefractive interaction to generate phase conjugate waves with an orthogonal polarization to an incident beam. The use of Ar+ laser and BaTiO3 crystal in an experiment for the cross polarized MPPCM found that diffraction efficiency for an extraordinary beam is about 20%. As opposed to a conventional parallel polarized MPPCM in which the use of a beam splitter is required to separate a diffraction beam, the cross polarized MPPCM can efficiently extract phase conjugate waves by means of a polarized beam splitter, demonstrating the advantage of substantially improved efficiency. (c) 2006 Elsevier Ltd. All rights reserved., ELSEVIER SCI LTD, English

Selective erasure for multiplexed holograms in Photorefractive crystal using phase conjugator
Takayuki Sano, Atsushi Okamoto, Kunihiro Sato, Masatoshi Bunsen, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 46, 6B, 3822, 3827, Jun. 2007
A novel selective erasure method for multiplexed holograms in a photorefractive crystal using a phase conjugator is presented. In this method, the pi-phase shift effect on the diffracted beam due to the photorefractive effect is used. There is a pi-phase shift between the interference pattern formed by the reading and diffraction beams, and that formed in the recording process. By returning the reading and reconstructed beams to a recording medium with a phase conjugator, the hologram can be selectively erased in parallel with the readout. Therefore, a dynamic selective erasure can be realized without requiring the accurate alignment of the selective erasure beams. The calculations using coupled-wave equations and experiment results demonstrate the implementability of our method. Furthermore, we analytically determine the requisite conditions of incident beams in the selective erasure process for the reduction of the decay of other multiplexed holograms., INST PURE APPLIED PHYSICS, English

Coherent parallel copying of holograms recorded by spatial spread-spectrum multiplexing
Terumasa Ito, Atsushi Okamoto, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 46, 6B, 3816, 3821, Jun. 2007
In this paper, we propose a new parallel hologram copying system in which multiplexed holograms are coherently copied from a master medium to a copy medium. The diffraction efficiency in spatial spread-spectrum multiplexing, which is a type of phase multiplexing based on phase modulation onto signals, can be significantly enhanced by coherent parallel copying. We theoretically and experimentally showed that the diffraction efficiency of M multiplexed holograms can be increased up to 1/M of that of a single hologram, which is an improvement by a factor of M compared with the 1/M-2 formula in conventional multiplexing systems., INST PURE APPLIED PHYSICS, English

Selective erasure of holograms in Photorefractive and photopolymer materials for rewritable and secure data storage
Masatoshi Bunsen, Hirosuke Furuta, Atsushi Okamoto, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 46, 6B, 3858, 3861, Jun. 2007
A selective erasure/update method of multiplexed photorefractive and photopolymer holograms by use of the double Mach-Zehnder (DMZ) interferometric arrangement is proposed. The DMZ arrangement is used as the optical phase-control device for holographic recording/erasure/update operations, which can produce a pair of pi-phase-shifted interference patterns with a simple optical setup. We intend to erase the holograms recorded in not only the inherently rewritable photorefractive crystal but also the photopolymer material generally used for the write-once (i.e., unerasable) holographic recording. It is experimentally confirmed that our method can erase the write-once type photopolymer holograms as well as the photorefractive holograms, although there will be a certain degree of restriction on the rewrite cycles limited by the monomer density, the degree of multiplexing and so on., INST PURE APPLIED PHYSICS, English

Coherent parallel copying of holograms recorded by spatial spread-spectrum multiplexing
Terumasa Ito, Atsushi Okamoto, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 46, 6B, 3816, 3821, Jun. 2007
In this paper, we propose a new parallel hologram copying system in which multiplexed holograms are coherently copied from a master medium to a copy medium. The diffraction efficiency in spatial spread-spectrum multiplexing, which is a type of phase multiplexing based on phase modulation onto signals, can be significantly enhanced by coherent parallel copying. We theoretically and experimentally showed that the diffraction efficiency of M multiplexed holograms can be increased up to 1/M of that of a single hologram, which is an improvement by a factor of M compared with the 1/M-2 formula in conventional multiplexing systems., INST PURE APPLIED PHYSICS, English

Selective erasure of holograms in Photorefractive and photopolymer materials for rewritable and secure data storage
Masatoshi Bunsen, Hirosuke Furuta, Atsushi Okamoto, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 46, 6B, 3858, 3861, Jun. 2007
A selective erasure/update method of multiplexed photorefractive and photopolymer holograms by use of the double Mach-Zehnder (DMZ) interferometric arrangement is proposed. The DMZ arrangement is used as the optical phase-control device for holographic recording/erasure/update operations, which can produce a pair of pi-phase-shifted interference patterns with a simple optical setup. We intend to erase the holograms recorded in not only the inherently rewritable photorefractive crystal but also the photopolymer material generally used for the write-once (i.e., unerasable) holographic recording. It is experimentally confirmed that our method can erase the write-once type photopolymer holograms as well as the photorefractive holograms, although there will be a certain degree of restriction on the rewrite cycles limited by the monomer density, the degree of multiplexing and so on., INST PURE APPLIED PHYSICS, English

Mutually pumped phase conjugate mirror using cross polarized photorefractive coupling
Atsushi Okamoto, Satoshi Honma, Shunsuke Uemura, Terumasa Ito, OPTICS AND LASER TECHNOLOGY, 39, 4, 881, 884, Jun. 2007
This paper presents a new proposal for a mutually pumped phase conjugate mirror (MPPCM) using cross polarization. In the cross polarized MPPCM, two light beams, whose polarizations are orthogonal to each other, incident on a photorefractive crystal, Causing photorefractive interaction to generate phase conjugate waves with an orthogonal polarization to an incident beam. The use of Ar+ laser and BaTiO3 crystal in an experiment for the cross polarized MPPCM found that diffraction efficiency for an extraordinary beam is about 20%. As opposed to a conventional parallel polarized MPPCM in which the use of a beam splitter is required to separate a diffraction beam, the cross polarized MPPCM can efficiently extract phase conjugate waves by means of a polarized beam splitter, demonstrating the advantage of substantially improved efficiency. (c) 2006 Elsevier Ltd. All rights reserved., ELSEVIER SCI LTD, English

Nondestructive readout of a photorefractive hologram by phase-conjugate copying in a one-crystal configuration
Applied Optics, 46, 13, 2443, 2452, 01 May 2007
English

Secure holographic memory by two-wave encryption method with a photorefractive crystal
Atsushi Okamoto, Akifumi Mita, Hisatoshi Funakoshi, Kiyoshi Moritake, Takayuki Sano, JOURNAL OF MODERN OPTICS, 54, 4, 599, 609, Mar. 2007
We propose a new all-optical encryption technique, which is a two-wave encryption method, and discuss security and holographic memory using this technique. Unlike the DRPE method, this technique is characterized by its ability to reduce output intensity for unauthorized memory access, along with the property to output a recorded white-noise image. Thus, the monitoring of output intensity achieves easy detection of unauthorized access. According to our numerical simulation, a particularly significant difference can be found in Output intensity, with a correlation coefficient of 20% or under between a key using unauthorized access and a compatible key to find detection sensitivity of unauthorized access. Robustness can be readily improved by increasing key length, and the probability was observed to be 10(-6) or under on identifying a randomly generated key with a key length of about 32 x 32 for the compatible key, even though the key length is too small. It is shown experimentally that the use of a compatible key reproduced a clear original image, but unauthorized key-based reproduction reduced output strength to approximately 1/20., TAYLOR & FRANCIS LTD, English

Secure holographic memory by two-wave encryption method with a photorefractive crystal
Atsushi Okamoto, Akifumi Mita, Hisatoshi Funakoshi, Kiyoshi Moritake, Takayuki Sano, JOURNAL OF MODERN OPTICS, 54, 4, 599, 609, Mar. 2007
We propose a new all-optical encryption technique, which is a two-wave encryption method, and discuss security and holographic memory using this technique. Unlike the DRPE method, this technique is characterized by its ability to reduce output intensity for unauthorized memory access, along with the property to output a recorded white-noise image. Thus, the monitoring of output intensity achieves easy detection of unauthorized access. According to our numerical simulation, a particularly significant difference can be found in Output intensity, with a correlation coefficient of 20% or under between a key using unauthorized access and a compatible key to find detection sensitivity of unauthorized access. Robustness can be readily improved by increasing key length, and the probability was observed to be 10(-6) or under on identifying a randomly generated key with a key length of about 32 x 32 for the compatible key, even though the key length is too small. It is shown experimentally that the use of a compatible key reproduced a clear original image, but unauthorized key-based reproduction reduced output strength to approximately 1/20., TAYLOR & FRANCIS LTD, English

Ultralow-loss optical quantum information processing in photonic bandgap devices
Hiroyuki Nihei, Atsushi Okamoto, PHOTON COUNTING APPLICATIONS, QUANTUM OPTICS, AND QUANTUM CRYPTOGRAPHY, 6583, 656830Q.1-656830Q.8, 2007
We have demonstrated the coherent control of photonic bandgap (PBG) devices composed of a three-level atom embedded in three-dimensional PBG structures, which enables us to strongly suppress the loss of quantum information not only during its storage but also during its processing. We find that this ultralow-loss optical quantum information processing can be realized by generating the upper atomic level splitting inside the PBG and by tuning one of the split levels to a dark line in the emission spectrum (zeros in the spectrum at certain values of the emitted photon frequency). Furthermore, we show that the coherent control may provide a basis for the universal quantum logic gate operation in quantum computing., SPIE-INT SOC OPTICAL ENGINEERING, English

Quantum information processing using nanoscale objects embedded in photonic crystals
Hiroyuki Nihei, Atsushi Okamoto, OPTOMECHATRONIC MICRO/NANO DEVICES AND COMPONENTS III, 6717, 671703.1-671703.8, 2007
We have demonstrated the coherent control of nanoscaleobjects (such as quantum dots) embedded in photonic crystals, which provides a basis for a one-qubit phase rotation gate that is one of the universal quantum logic gates for quantum information processing. In this demonstration, the quantum electrodynamics of the atomic system is calculated by the Schrodinger equation. Using the results of the calculation, the quantum electrodynamics is graphically represented by a Bloch sphere. This shows that the quantum state is rotated on the Bloch sphere, and this rotation is stopped or started, depending on the laser phase, which can act as a one-qubit phase rotation gate., SPIE-INT SOC OPTICAL ENGINEERING, English

High-speed holographic read-only memory replication systems with two-wave and four-wave photorefractive amplifier
Terumasa Ito, Atsushi Okamoto, Nobuhiro Takahashi, Takayuki Sano, OPTICAL DATA STORAGE 2007, 6620, 66201B.1-66201B.7, 2007
Copying speed is an important characteristic for optical read-only memory (ROM) replication systems. The copying speed of holographic ROM replication is, however, limited by small energy efficiency of the optical system due to the small diffraction efficiency of multiplexed holograms. In this paper we propose new holographic ROM replication systems with a photorefractive amplifier, and analyze the speed gain performance. We improve energy efficiency significantly and speed up replication by amplifying weak diffraction signal beams using photorefractive wave mixing. Our new theory and numerical calculations revealed that achievable speed gain can be evaluated from only a single dimensionless parameter that is the product of the three as follows: (i) the pump beam intensity ratio in the amplifier, (ii) the ratio of the photopolymer and photorefractive sensitivities, and (iii) the dynamic range per hologram of the copy medium. In current holographic recording systems, a practical copying speed gain of more than 10 is achievable with currently available photorefractive materials., SPIE-INT SOC OPTICAL ENGINEERING, English

Analysis of composite interpage crosstalk in shift multiplexing　　　　　　　　　　　　　　　
IWHM 2007 Digests, 1st International Workshop on Holographic Memories 2007, no.26p13, 2007

Improvement of holographic recording configuration for data page rewriting　　　　　　　　　　　　　　　
Technical Digest of International Symposium on Optical Memory 2007 (ISOM’07), no. We-J-01, 2007

Targeted control of a quantum dot in photonic crystals for a nanoscale optical memory　　　　　　　　　　　　　　　
Technical Digest of International Symposium on Optical Memory 2007 (ISOM’07), no. We-I P05, 2007

Decay Reduction of Multiplexed Holograms on Selective Erasure by Amplified Phase Conjugate Beams　　　　　　　　　　　　　　　
Technical Digest of International Symposium on Optical Memory 2007 (ISOM’07), no.We-J-18, 2007

Security Improvement by Multiplexing Dummy Data for Optical Random Phase Encryption　　　　　　　　　　　　　　　
Technical Digest of International Symposium on Optical Memory 2007 (ISOM’07), no.We-J-21, 2007

Improvement in copying speed and diffraction efficiency of holographic ROMs by photorefractive amplification and coherent parallel copying　　　　　　　　　　　　　　　
Technical Digest of International Symposium on Optical Memory 2007 (ISOM’07), no.Th-K-08, 2007

Noise reduction strategy in high-speed replication of holographic memories using photorefractive amplification
Nobuhiro Takahashi, Atsushi Okamoto, Takayuki Sano, Terumasa Ito, 2007 PACIFIC RIM CONFERENCE ON LASERS AND ELECTRO-OPTICS, VOLS 1-4, 609, 610, 2007
We propose a high-speed replication system using photorefractive amplification for holographic memories. Also, we show a noise reduction strategy that enables to ensure a high signal-to-noise ratio of replicated holograms by using a transient gain of photorefractive amplification., IEEE, English

Intrapage crosstalk in one-beam holographic recording system using a blazed grating
Joji Sasaki, Atsushi Okamoto, Terumasa Ito, Eiji Nakagawa, Toshio Ando, Hiroshi Umehara, 2007 PACIFIC RIM CONFERENCE ON LASERS AND ELECTRO-OPTICS, VOLS 1-4, 425, +, 2007
We analyzed intrapage crosstalk characteristics in the one-beam holographic recording system in which a hologram is recorded with a signal and its diffraction beam split by a blazed grating. Calculations show that low-crosstalk holographic reconstruction can be achieved even with a non-modulated reference beam by optimizing the optical system., IEEE, English

Time-domain differential detection using photorefractive two-wave mixing in phase-only holographic data storage system
Masanori Takabayashi, Atsushi Okamoto, Terumasa Ito, 2007 PACIFIC RIM CONFERENCE ON LASERS AND ELECTRO-OPTICS, VOLS 1-4, 607, 608, 2007
We propose a new method for detection of phase-modulated signals that provides higher energy efficiency detection and simplified alignments of position and intensity between interference images. By using time-domain differential detection with 2x over sampling, phase-modulated signals can be exactly distinguished., IEEE, English

Recording schedule for partially-coherent hologram multiplexing in a photorefractive medium
ITO Terumasa, OKAMOTO Atsushi, SATO Kunihiro, Applied Optics, 46, 23, 5902, 5911, 2007

All-optical tunable wavelength filter using photorefractive material　　　　　　　　　　　　　　　
Technical Digest of 12th Optoelectronics and Communications Conference (OECC2007), no.10E1-4, 2007

Apodization of photorefractive transmission grating for wavelength filter　　　　　　　　　　　　　　　
Technical Digest of 12th Optoelectronics and Communications Conference (OECC2007), no.12E2-5, 2007

All-optical interconnection for two-dimensional data using photorefractive organic film　　　　　　　　　　　　　　　
Technical Digest of 12th Optoelectronics and Communications Conference (OECC2007), no.11P-32, 2007

Optical Parallel Interconnects Using Organic Photorefractive Polymer　　　　　　　　　　　　　　　
Technical Digest of 12th Optoelectronics and Communications Conference (OECC2007), no.11P-34, 2007

Nondestructive readout of a photorefractive hologram using phase-conjugate copying in a one-crystal configuration
ITO Terumasa, OKAMOTO Atsushi, FUNAKOSHI Hisatoshi, SATO Kunihiro, Applied Optics, 46, 13, 2443, 2452, 2007

High-speed holographic read-only memory replication systems with two-wave and four-wave photorefractive amplifier
Terumasa Ito, Atsushi Okamoto, Nobuhiro Takahashi, Takayuki Sano, OPTICAL DATA STORAGE 2007, 6620, no.TuD2, 2007
Copying speed is an important characteristic for optical read-only memory (ROM) replication systems. The copying speed of holographic ROM replication is, however, limited by small energy efficiency of the optical system due to the small diffraction efficiency of multiplexed holograms. In this paper we propose new holographic ROM replication systems with a photorefractive amplifier, and analyze the speed gain performance. We improve energy efficiency significantly and speed up replication by amplifying weak diffraction signal beams using photorefractive wave mixing. Our new theory and numerical calculations revealed that achievable speed gain can be evaluated from only a single dimensionless parameter that is the product of the three as follows: (i) the pump beam intensity ratio in the amplifier, (ii) the ratio of the photopolymer and photorefractive sensitivities, and (iii) the dynamic range per hologram of the copy medium. In current holographic recording systems, a practical copying speed gain of more than 10 is achievable with currently available photorefractive materials., SPIE-INT SOC OPTICAL ENGINEERING, English

Efficient coupling for bidirectional pumping in EDFA with two mutually-pumped phase-conjugate mirrors
Shugo Kano, Atsushi Okamoto, Yoshihisa Takayama, Kunihiro Sato, NONLINEAR OPTICS AND APPLICATIONS II, 6582, 65821U1-65821U9, 2007
We propose a new LD-fiber-coupling-method for bidirectionally-pumped erbium-doped fiber amplifier (EDFA) using two mutually-pumped phase-conjugate mirrors (MPPCMs). MPPCM is formed by two mutually incoherent beams in photorefractive crystal (PRC) and can convert each incident beam into each phase-conjugate beam of them. Owing to mode conversion by phase-conjugate characteristics, the coupling loss due to mode mismatching between a pump beam and a fiber is improved. Therefore, precision lens and lensed fiber for mode matching are not required. Additionally, because photorefractive index gratings that compose a MPPCM are rewritable in real time, MPPCM can dynamically adapt to a variety of system error factors, such as misalignment of components, mode conversion generated by LDs or fibers with defects. In our system, the overall coupling efficiency of pump beams is mainly determined by diffraction efficiency of MPPCMs that depends on the photorefractive coupling strength and the intensity ratio of two incident beams. However, achievable diffraction efficiency in this system is restricted by optical loss between two MPPCMs. This is because the transmitted pump beams passing through the EDF are reused for forming the opposite MPPCM. To achieve a high signal amplification gain, absorption loss of pump beam powers in the EDF is unavoidable. Therefore, we analytically and experimentally evaluate the acceptable loss between two PRCs to form both MPPCMs., SPIE-INT SOC OPTICAL ENGINEERING, English

Tunable optical filter for wavelength division multiplexing using photorefractive planar waveguide
Satoshi Honma, Hirokazu Ito, Mitsuhiro Komatsu, Shinzo Muto, Atsushi Okamoto, NONLINEAR OPTICS AND APPLICATIONS II, 6582, 65821S1-65821S9, 2007
In this paper, we propose a tunable optical filter using a photorefractive planar waveguide. The index grating generated by the control beam drops off a part of wavelength components in the wavelength division multiplexed signal beam. It make possible to select the wavelength components of the signal beam by optically adjusting the wave vector of the grating. The photorefractive effect is one of the most efficient nonlinear effects, and therefore the signal beam can be controlled by the relative low beam power. The proposed optical filter can be applied to an active add-drop module when the signal beam is fed back to the module as a control beam. Therefore, it contribute to development of the all-optical network systems. It is also able to apply to photonic label processing technology by multiplexing the index gratings. We investigated the signal beam propagation and the permittivity distribution in the photorefractive waveguide by using a finite dimensional beam propagation method (FD-BPM) and analyzed the filtering property. Considering the two optical setups using the transmission and reflection grating, we compared these performances., SPIE-INT SOC OPTICAL ENGINEERING, English

Splice of photonic crystal fibres by use of double phase-conjugate mirror
Yusuke Nakayama, Atsushi Okamoto, Yoshihisa Takayama, Yutaka Hayano, PHOTONIC CRYSTAL FIBERS, 6588, 6588131, 6588138, 2007
We present a novel splicing method for photonic crystal fibres (PCFs) with a double phase-conjugate mirror (DPCM). The DPCM is an optical device with photorefractive crystal (PRC) which generatEs phase-conjugate beams easily. In this report, we experimentally measure the splice losses of the DPCM for transverse PCF offset. We numerically estimate the splice losses in the case that butt coupled PCFs without DPCM. Comparing the experimental and numerical values of the splice loss of PCFs, we discuss the tolerance of the DPCM for the PCF displacement. Also, we discuss the causes of loss inside the DPCM module., SPIE-INT SOC OPTICAL ENGINEERING, English

Experiment on long-term readout of binarized image in photorefractive memory with double mutually pumped phase conjugators
Optics & Laser Technology, 38, 8, 604, 613, Nov. 2006
English

Experiment on long-term readout of binarized image in photorefractive memory with double mutually pumped phase conjugators
H Funakoshi, A Okamoto, OPTICS AND LASER TECHNOLOGY, 38, 8, 604, 613, Nov. 2006
We demonstrate long-term readout of a binarized image with a dynamic refreshment technique by mutually pumped phase conjugate mirrors (MPPCMs). Long-term continuous readout without any fixing technique can be achieved by the refreshment with image-bearing beam resonance between the phase conjugate mirrors. Our technique additionally offers image binarization by intensity thresholding of MPPCM without any external image processing systems. In this paper, we show grayscale-to-binary conversion as well as long-term readout can be realized by adjusting the appropriate incident beam intensities and the coupling strength of crystals. We perform recording and retrieving experiment with barium titanate crystals and demonstrate the binarized image can be reconstructed over 10 min in the double MPPCM configuration. (C) 2005 Elsevier Ltd. All rights reserved., ELSEVIER SCI LTD, English

Selective erasure of speckle-multiplexed holograms by use of a double Mach-Zehnder interferometric arrangement
Applied Optics, 45, 27, 7035, 7042, 20 Sep. 2006
English

Volume holographic recording using spatial spread-spectrum multiplexing
T Ito, A Okamoto, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 45, 2B, 1270, 1276, Feb. 2006
A new recording method called spatial spread-spectrum (SSS) multiplexing, which is particularly suitable for holographic disc recording, is proposed. Multiplexing holograms by phase modulation and demodulation onto the signal beams themselves (not onto reference beams) provides a new degree of freedom in the design of holographic storage systems, thereby making it possible to improve storage density by combining with other multiplexing methods. In our newly proposed recording geometry with spatial filtering, uncorrelated noise coming from undesired pages can be efficiently deflected away from a detector. Calculations show that the theoretically achievable multiplicity of the SSS recording system with spatial filtering is improved up to 70 when the numerical aperture (NA) of the signal beam is 0.1., INST PURE APPLIED PHYSICS, English

Volume holographic recording using spatial spread-spectrum multiplexing
T Ito, A Okamoto, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 45, 2B, 1270, 1276, Feb. 2006
A new recording method called spatial spread-spectrum (SSS) multiplexing, which is particularly suitable for holographic disc recording, is proposed. Multiplexing holograms by phase modulation and demodulation onto the signal beams themselves (not onto reference beams) provides a new degree of freedom in the design of holographic storage systems, thereby making it possible to improve storage density by combining with other multiplexing methods. In our newly proposed recording geometry with spatial filtering, uncorrelated noise coming from undesired pages can be efficiently deflected away from a detector. Calculations show that the theoretically achievable multiplicity of the SSS recording system with spatial filtering is improved up to 70 when the numerical aperture (NA) of the signal beam is 0.1., INST PURE APPLIED PHYSICS, English

All-optical XOR-, OR-, and AND-gates using Photorefractive Two-Wave Mixing
5th, 213, 214, 2006
English

Coherent control of excited atomic states inside a photonic band gap
Hiroyuki Nihei, Atsushi Okamoto, PHOTONIC CRYSTAL MATERIALS AND DEVICES III (I.E. V), 6182, 61821B.1-61821B.8, 2006
We demonstrate the coherent control of the excited states of the atom embedded in a photonic band gap (PBG) structure by means of a Rabi oscillation. In this demonstration, we show that the atomic decay is strongly suppressed not only during the Rabi oscillation but also during switching process to the final steady state. This switching is achieved by eliminating one of localized field modes arising from the localization of the emitted photon in the vicinity of the atom due to the PBG, where the suppression of the atomic decay during the switching is facilitated by achieving this elimination not outside the PBG but inside the PBG. Such a coherent control of excited states without the atomic decay suggests the possibility of extending the atomic system for quantum computing to act as nearly lossless., SPIE-INT SOC OPTICAL ENGINEERING, English

Shift Margin of a Random Diffuser in Spatial Spread-Spectrum Multiplexing
5th, 187, 188, 2006
English

All-optical XOR-, OR-, and AND-Gates using Photorefractive Two-Wave Mixing　　　　　　　　　　　　　　　
5th International Conference of Optics-photonics Design & Fabrication (ODF’06) Technical Digest, no. 7PS4-04, 2006

Shift margin of a random diffuser in spatial spread-spectrum multiplexing　　　　　　　　　　　　　　　
5th International Conference of Optics-photonics Design & Fabrication (ODF’06) Technical Digest, no.7PS3-06, 2006

Selective erasure of photorefractive and photopolymer holograms for rewriteable and secure data storage　　　　　　　　　　　　　　　
Technical Digest of International Symposium on Optical Memory 2006 (ISOM 2006), no.Th-I-43, 2006

Elimination of edge enhancement on hologram refresh system using two photorefractive crystals　　　　　　　　　　　　　　　
Technical Digest of International Symposium on Optical Memory 2006 (ISOM 2006), no.Th-I-30, 2006

Reduction of decay of multiplexed holograms in selective erasure using phase conjugate mirror　　　　　　　　　　　　　　　
Technical Digest of International Symposium on Optical Memory 2006 (ISOM 2006), no.Th-I-31, 2006

One-beam holographic recording using a blazed grating　　　　　　　　　　　　　　　
Technical Digest of International Symposium on Optical Memory 2006 (ISOM 2006), no.Th-I-45, 2006

Coherent parallel copying of holographic recorded by spatial spread-spectrum multiplexing
ITO T., Tech. Dig. ISOM2006, no.Mo-D-07, 2006

Shift-phase code multiplexing technique for holographic memory　　　　　　　　　　　　　　　
Technical Digest of International Symposium on Optical Memory 2006 (ISOM 2006), no.Th-I-44, 2006

Selective erasure of speckle-multiplexed holograms by use of a double Mach-Zehnder interferometric arrangement
BUNSEN Masatoshi, FURUTA Hirosuke, OKAMOTO Atsushi, Applied Optics, 45, 27, 7035, 7042, 2006

Estimation of crosstalk in holographic optical interconnection with shift-phase code multiplexing　　　　　　　　　　　　　　　
Technical Digest of 11th Optoelectronics and Communications Conference (OECC2006), no.5E3-2, 2006

Optical interconnection with photorefractive connection module by using polymeric material　　　　　　　　　　　　　　　
Technical Digest of 11th Optoelectronics and Communications Conference (OECC2006), no.4P-8, 2006

All-optical logic gates using photorefractive two-wave mixing for two-dimensional information processing　　　　　　　　　　　　　　　
Technical Digest of 11th Optoelectronics and Communications Conference (OECC2006), no.6B2-3, 2006

Ultra low-less coherent control of excited atomic states in photonic bandgap　　　　　　　　　　　　　　　
Technical Digest of 11th Optoelectronics and Communications Conference (OECC2006), Post Deadline Paper, 2006

Coherent control of excited atomic states inside a photonic band gap
Hiroyuki Nihei, Atsushi Okamoto, PHOTONIC CRYSTAL MATERIALS AND DEVICES III (I.E. V), 6182, 61821B, 2006
We demonstrate the coherent control of the excited states of the atom embedded in a photonic band gap (PBG) structure by means of a Rabi oscillation. In this demonstration, we show that the atomic decay is strongly suppressed not only during the Rabi oscillation but also during switching process to the final steady state. This switching is achieved by eliminating one of localized field modes arising from the localization of the emitted photon in the vicinity of the atom due to the PBG, where the suppression of the atomic decay during the switching is facilitated by achieving this elimination not outside the PBG but inside the PBG. Such a coherent control of excited states without the atomic decay suggests the possibility of extending the atomic system for quantum computing to act as nearly lossless., SPIE-INT SOC OPTICAL ENGINEERING, English

Efficient pump beam coupling in EDFA with two Mutually Pumped Phase Conjugate Mirrors
Shugo Kano, Atsushi Okamoto, Yoshihisa Takayama, Kunihiro Sato, Hideyuki Kaseda, RELIABILITY OF OPTICAL FIBER COMPONENTS, DEVICES, SYSTEMS, AND NETWORKS III, 6193, 61930F, 2006
In the bidirectional pumped Erbium Doped Fiber Amplifier (EDFA), we propose the new method with two Mutually Pumped Phase Conjugate Mirrors (MPPCMs) to couple the pump beam into the fiber. This method makes it possible to couple the pump beam into the propagation mode of the fiber without high precision adjustment by the characteristic of MPPCM. Additionally, high precision readjustment is not required when a LD, fiber or lens is exchanged due to failures. In our method it is important to obtain high diffraction efficiency of MPPCM for high coupling efficiency between the pump beam and the fiber. Diffraction efficiency of MPPCM depends on the intensity ratio of two incident beam intensities inside the PRC. We analyze the coupling efficiency for the intensity ratio of two pump beams, and show the optimum intensity ratio of two pump beams. Then, we perform an experiment to couple the pump beam (Ar' laser 514.5nm) to the fiber (multimode fiber of 62.5 mu m core diameter). In the experiment, coupling efficiency higher than 35% was confirmed. Moreover, in our method, the time to complete the coupling depends on the beam intensities in the early stage of the process. Therefore, we also propose the 4f imaging system to achieve a faster coupling at the early stage, and design the optical system to improve the time to complete the coupling in our method., SPIE-INT SOC OPTICAL ENGINEERING, English

Optical intersatellite data transmission with phase conjugate mirror for formation flying
Tatsuya Shiratori, Atsushi Okamoto, Yoshihisa Takayama, Terumasa Ito, PHOTON MANAGEMENT II, 6187, U418, U425, 2006
We propose a new optical intersatellite communications system with a phase conjugate mirror (PCM) information flying (IFF). In conventional optical intersatellite communications, high-accurate target acquisition and tracking are required for both the transmitter and the receiver. In our system with a PCM, when a control beam from the receiver is captured by a PCM in the transmitter, the signal beam from the transmitter introduced back to the receiver as its phase-conjugate replica. Thus, it is not necessary for the transmitter to target the receiver. Another advantage of using a PCM is that we can utilize spatial filtering. Background noise by sunlight with the laser wavelength can also be efficiently suppressed by a spatial phase modulation/demodulation and filtering processes using phase compensation by the PCM, which leads to the improvement of the signal-to-noise ratio (SNR) and hence provides high data transmission rates in the system. In order to efficiently filter out the background noise, a large beam propagation angle is required in spatial filtering. We spatially modulate the background noise by the diffuser and reduce the beam diameter by the expansion/downscale optical system as a method to enlarge the beam propagation angle.
In this paper, we show that our system can separate the noise from the signal by using the expansion/downscale optical system even under spatial phase modulation. In the analysis, the SNR is 32.6[dB] at scale = 8.0 x 10(4), when a spatial phase modulation by the diffuser is theta = 1.5 x 10(-5) [rad]., SPIE-INT SOC OPTICAL ENGINEERING, English

Fault tolerant function of dynamic refreshing holographic memory with shutter-less optical feedback circuit
A Okamoto, T Ito, M Bunsen, Y Takayama, JOURNAL OF MODERN OPTICS, 52, 17, 2453, 2465, Nov. 2005
The optical system, consisting of two photorefractive memories and a shutter-less optical feedback circuit, will be demonstrated to function as data mirroring. This function is known to automatically detect the data dropout and restore data, using unimpaired data in another memory, in the event that part or all of the data in either of them were lost for some reason. This memory system also can cope with a damaged hologram, a result of reading beams, which is a disadvantage of rewritable photorefractive memory, to ensure non-destructive holographic reading. It can be achieved by using no electronic circuits or mechanical structures; our optical experimental method in particular obtains this basic action., TAYLOR & FRANCIS LTD, English

A-7-14 Security enhancement by dummy data multiplexing for optical encryption method using random phase code
Moritake Kiyoshi, Okamoto Atushi, Sano Takayuki, Proceedings of the Society Conference of IEICE, 2005, 187, 187, 07 Sep. 2005
The Institute of Electronics, Information and Communication Engineers, Japanese

C-3-47 Encryption method with photorefractive inverse filter
Honma Satoshi, Higuchi Tomomi, Muto Shinzo, Okamoto Atsushi, Proceedings of the Society Conference of IEICE, 2005, 1, 191, 191, 07 Sep. 2005
The Institute of Electronics, Information and Communication Engineers, Japanese

C-13-1 Image Cross Connecter with Photorefractive Polymer
Muranaka Hidenobu, Okamoto Atsushi, Bunsen Masatoshi, Yamamoto Michiharu, Proceedings of the Society Conference of IEICE, 2005, 2, 123, 123, 07 Sep. 2005
The Institute of Electronics, Information and Communication Engineers, Japanese

Suppression of Fanning Noise for Holographic Memory with Refresh System
ISHII Hiroyuki, OKAMOTO Atsushi, ITO Terumasa, Technical report of IEICE. LQE, 105, 251, 31, 34, 19 Aug. 2005
Holographic memory with the refresh system using two photorefractive crystals is expected to realize Holographic Random Access Memory(RAM). However, in this method, it is necessary to defeat fanning noise that is main cause of degradation of output signal and decrease in SNR. We propose a new optical noise filter system using a random phase diffuser, which can be used in holographic refresh systems to obtain high quality output signal and achieve higher SNR, by suppression of fanning noise between the two crystals., The Institute of Electronics, Information and Communication Engineers, Japanese

Efficient Coupling of Pump Beam using Two Mutually Phase conjugate Minors in EDFA
KASEDA Hideyuki, OKAMOTO Atsushi, TAKAYAMA Yoshihisa, Technical report of IEICE. LQE, 105, 251, 45, 50, 19 Aug. 2005
We propose a new method to coupled a pump beam to a fiber using two mutually phase conjugate mirrors (MPPCMs). According to characteristic of MPPCM, a pump beam is coupled to a fiber as the phase conjugate beam of the beam from the fiber. Therefore, we can obtain high coupling efficiency without the processing technique and precision adjustment. The coupling efficiency in this method depends on the intensity ration of two incident beam in the photorefractive crystal. We analyze the coupling efficiency for the ratio of two pump beams, and then show the optimum ratio of two pump beams, The Institute of Electronics, Information and Communication Engineers, Japanese

Long-term reading experiment on a photorefractive holographic memory with the hologram sustainment technique by optical feedback
H Funakoshi, A Okamoto, K Sato, JOURNAL OF MODERN OPTICS, 52, 11, 1511, 1527, Jul. 2005
We demonstrate a long-term continuous readout of a two-dimensional image in a photorefractive holographic memory with a BaTiO3 crystal. A considerable extension of reading time is achieved by use of a hologram sustainment technique with an optical feedback circuit. Hologram rewritings by the simultaneous illumination of the reading beam and the feedback beam, which is incident on a crystal from the opposite direction to the reading beam, contribute to all-optical hologram sustainment without any. xing technique. In this paper, the effectiveness of the hologram sustainment technique is explained by the analysis of the temporal property of the amplitude of the index grating in a crystal. By calculating the temporal properties of the reconstructed beam intensity, we reveal the feedback rate and the coupling strength for high output efficiency. We perform an experiment on two-dimensional image reading and writing with a 45 degrees cut BaTiO3 crystal and show that a recorded image can be reconstructed over 20 min without critical image degradation whereas a reconstructed image fades away within 20 s in the conventional readout technique., TAYLOR & FRANCIS LTD, English

Mutually pumped phase conjugate mirror with cross-polarized beams and all-optical bus system
HONMA Satoshi, KISHIHARA Syunsuke, OKAMOTO Atsushi, MUTO Shinzo, Technical report of IEICE. OCS, 105, 120, 1, 6, 10 Jun. 2005
We propose a mutually pumped phase conjugate mirror (MPPCM) with cross-polarized beams. The incident beams and the generated phase conjugation beams are orthogonal polarized each other, and the optical passes are efficiently divided by using a polarized beam splitter. Therefore it is possible to suppress the energy loss of the beams compared with conventional MPPCM with parallel-polarized beams. We investigate the coupling strength threshold for buildup of the cross-polarized MPPCM and the optimum intensity ratio of the incident beams. Comparison of the numerical analysis with a basic experiment is given. A qualitative agreement is exhibited. In the end, we suggest the application of the CP-MPPCM to an all-optical bus system., The Institute of Electronics, Information and Communication Engineers, Japanese

Theoretical and experimental studies of hologram multiplexing that uses a random wave front generated by photorefractive beam fanning.
Applied Optics, 44, 8, 1454, 1463, 10 Mar. 2005
English

COHERENT CONTROL OF A QUBIT EMBEDDED IN PHOTONIC CRYSTALS USING A DARK LINE IN EMISSION SPECTRA
13, 17, 20, Mar. 2005
English

Improvement of coupling efficiency between pump light source and fiber in EDFA using mutually pumped phase conjugate mirrors
H Kaseda, A Okamoto, Y Takayama, H Kato, 2005 PACIFIC RIM CONFERENCE ON LASERS AND ELECTRO-OPTICS, 2005, 803, 804, 2005
We propose a new method of dynamic coupling between a pump light source and a fiber using mutually pumped phase conjugate mirrors. High efficient coupling is possible without a wedge shaped fiber and so on., IEEE, English

Experiment on all-optical bi-directional interconnection with double mutual-pumped phase conjugate mirrors
S Hondo, A Okamoto, K Sato, S Honma, OPTOELECTRONIC DEVICES AND INTEGRATION, PTS 1 AND 2, 5644, Pt.2, 549, 556, 2005
Recently the scheme of bi-directional optical communication with a mutual-pumped phase conjugate mirror (MPPCM) has attracted attention. Bi-directional communication enables the integration of devices because input port and output port can be shared. We propose a new design for an all-optical bi-directional interconnection with the double MPPCMs. This interconnection is composed of two photorefractive crystals and a polarized beam splitter which is located between the two crystals. The bi-directional connection is formed via two MPPCMs produced by illumination of the signal beams and the control beam. The wiring pattern can be reconfigured flexibly by changing the spatial distribution of the control beam without any adjustment of the signal beams. It is possible to combine and divide the optical pass of the signal beam and the control beam by using polarized beam splitter without loss because the signal beams and the control beam are orthogonal polarized. In addition, the signal beams transmitting through the two crystals enhance the MPPCMs efficiently under the appropriate condition. After buildup of MPPCMs, the connection is maintained without consecutive illumination of the control beam. Therefore self-holding is achieved and it enables the interconnection with lower power consumption. In this paper, we analyze the optimum intensity ratio of the control beam for the signal beam in order to shorten the time for establishment of connection. Moreover, as a basic experiment.. we confirm that the connection can be maintained by two MPPCMs after cutoff of the control beam by using a BaTiO3 crystals and an Ar+ laser., SPIE-INT SOC OPTICAL ENGINEERING, English

Photorefractive bi-directional connection module with mutual-pumped phase conjugate mirror
Kazumasa Kori, Atsushi Okamoto, Yoshihisa Takayama, Masatoshi Bunsen, Hisatoshi Funakoshi, Terumasa Ito, Proceedings of SPIE - The International Society for Optical Engineering, 5642, 487, 496, 2005
The purpose of this study is to apply a free-space optical interconnection to a reconfigurable board-to-board connection where the wiring patterns connecting boards are optically formed without electrical-optical conversion. We regard a photorefractive bi-directional connection module (PBCM) based on a mutually pumped phase conjugate mirror as a key device to construct such a connection network and employ PBCMs at input/output interfaces of each board. Although optical behaviors of PBCM are influenced by the exposure conditions, we especially focus on the diameter of beams illuminating photorefractive media placed inside PBCM so as to find some geometrical restrictions hi a design of networking system. Through numerical analyses, we show a sample configuration of PBCM for the board-to-board interconnection and present a conceptual design of input/output interface., English

Optical controlled matrix switch and free-space optical interconnection by photorefractive polymers
Atsushi Okamoto, Hisatoshi Funakoshi, Masatoshi Bunsen, Akinori Nishio, Proceedings of SPIE - The International Society for Optical Engineering, 5642, 599, 608, 2005
By irradiating alternative external light into the system with four-wave mixing in photorefractive polymers, the restriction on the generation of a phase conjugate beam or diffracted light will be demonstrated in this experiment. In addition, in order to verify the use of a two-dimensional array for simultaneous switching, the elimination of only part of diffraction grating recorded will be experimentally conducted., English

Experiment on signal extraction in photorefractive connection module with organic polymer PATPD
Kazuhiro Harasaka, Atsushi Okamoto, Masatoshi Bunsen, Michiharu Yamamoto, Proceedings of SPIE - The International Society for Optical Engineering, 6050, 60500V.1-60500V.8, 2005
We propose an optically controllable device Photorefractive Connection Module (PRCM) for free-space optical interconnection between boards. The optical signal composed of a large number of spatially divided channels passes through the photorefractive material which is core of PRCM. In the photorefractive material, diffraction gratings are induced only where the control beam and the pump beam are illuminated. The signal beams in desired spatial channels can be diffracted by setting an appropriate pattern of the control beam and extracted by separating from the control beam with a beam splitter. In this study, we use organic photorefractive polymer PATPD as the photorefractive material. Diffraction efficiency of PATPD is comparable with thick inorganic crystals although the thickness of PATPD is less than 1/10 of these crystals. Thin gratings have a large advantage for PRCM because the thickness of the gratings causes large crosstalk between spatial channels. In addition, the constraint of phase matching is reduced because the phase mismatch is proportional to the thickness of the material. The decrease of the phase mismatch provides large allowance for misalignment of incident angle of beams
therefore it becomes easy to adjust incident angles. We reveal the relation of diffraction efficiency to angular difference of PATPD by analysis and experiment. Diffraction efficiency decreases by half at the difference of 0.5°, which is about ten times larger than that of thick crystals. We demonstrate that it is possible to extract the signal beams in desired channels and reconfigure the extraction pattern according to optical control by using PATPD., English

Shift selectivity of spatial spread-spectrum holographic recording system
Terumasa Ito, Atsushi Okamoto, Masatoshi Bunsen, Proceedings of SPIE - The International Society for Optical Engineering, 6050, 605009.1-605009.8, 2005
Volume holographic recording is a promising solution for next-generation optical disc storage that has a high capacity more than 1 TB. This huge capacity is achieved by superimposing many holograms, each of which has millions of bits, at the same recording spot. We proposed a new technique, Spatial Spread Spectrum (SSS) multiplex recording in Ref 1. Unlike conventional multiplex holography based on Bragg effect of thick holograms, our technique utilizes spatial phase modulation and demodulation of the signal beam itself with a random diffuser to address the multiplexed page data. SSS multiplexing is additionally combined with other multiplexing methods, and provides further improvement of the total capacity of holographic storage. In this paper we experimentally verify the basic recording and readout feasibility, and investigate the shift selectivity and the aligning margin of the SSS holographic recording that are an important factor to determine the tolerance against vibration. It is shown that a clear 2-dimensional image is successfully reconstructed from the hologram even in the case the central part of the diffused signal beam is blocked in recording, and that a sharp shift selectivity about 5 μm was obtained by a diffuser with a diffusion angle of 15 degree, and the aligning margin for a sufficient SNR was approximately 1 μm., English

Selective erasure for multiplexed holograms in photorefractive crystal using phase conjugate mirror
Takayuki Sano, Atsushi Okamoto, Kunihiro Sato, Masatoshi Bunsen, Proceedings of SPIE - The International Society for Optical Engineering, 6050, 60500X.1-60500X.8, 2005
In this paper, we propose a selective erasure method for multiplexed holograms in a photorefractive crystal using a phase conjugate mirror (PCM). In this method, for the accurate selective erasure, we use π phase shift between the relative phase of the diffracted beam to the transmitted beam by the hologram in photorefractive crystal and the relative phase of the object beam to reference beam in recording process by setting the direction of c-axis to the appropriate direction. In the selective erasure process, the diffracted beam and the transmitted beam by the original hologram in main memory are returned to main memory by PCM. These returned beams automatically propagate through the strictly same pass as the diffracted beam and the transmitted beam. Furthermore, by these returned beams, the π-phase shifted hologram is overwritten on the original hologram by setting c-axis of main memory to the appropriate direction. Therefore, the π-phase shifted hologram is automatically overwritten on the strictly same position as the original hologram without the high precise alignment and the original hologram is selectively erased. We perform the analysis and the experiment on selective erasure and demonstrate that one of the multiplexed holograms is selectively erased with our method., English

Optimization of Incident Beam Intensities for Mutually Pumped Four-Wave Mixing and Multi-Valued Property of Phase Conjugation
HONMA Satoshi, AMANO Takashi, UEMURA Syunsuke, FUNAKOSHI Hisatoshi, OKAMOTO Atsushi, MUTO Shinzo, The IEICE transactions on electronics C, Vol.J88-C, 2, 91, 98, 2005
位相共役光学を応用した光デバイスの開発が盛んに行われており, 位相共役光の高効率かつ簡便な発生方法が求められている.我々はこれまでに相互励起型位相共役鏡と縮退4波混合を組み合わせた相互励起型4波混合を新たに提案した.本手法では互いに波面が一致しかつ対向に伝搬する理想的なポンプ光を自動的に作り出せるので, 入射する光の波面及び角度を微調整する必要はなく, 簡便に位相共役光を発生させることができる.その実験的検証に加えて, 相互励起型位相共役鏡のみを用いた場合よりも位相共役光の立上りが早くなることを示した.しかし, これまでに相互励起型4波混合の理論的な検討が行われていない.本論文では, 位相共役光発生の高効率化を図る目的から, フォトリフラクティブ相互励起型4波混合の二つの相互作用領域における結合強度を考慮に入れた位相共役変換効率を解析し, それぞれの結合強度に応じた最適な入射条件について検討を行う.また, 媒質の効率が高い場合に位相共役変換効率に複数の解が出現することを示し, その発生条件について検討を行う., The Institute of Electronics, Information and Communication Engineers, Japanese

「相互励起型位相共役鏡による揮発性ホログラムの全光学的維持手法」　　　　　　　　　　　　　　　
電子情報通信学会論文誌, Vol.J88-C, 4, 286, 289, 2005

Ito, T., Okamoto, A. and Bunsen, M.: “Shift selectivity of spatial spread-spectrum holographic recording system”, Proceedings of. SPIE(ISOT2005), Vol.6050-09(2005)＊*　　　　　　　　　　　　　　　
2005

「フォトニック結晶に埋め込まれた原子のラビ振動」　　　　　　　　　　　　　　　
電子情報通信学会論文誌, Vol.J88-C, 11, 998, 999, 2005

Kaseda, H., Okamoto, A., Y. Takayama and Kato, H.: “Improvement of Coupling Efficiency between Pump Light Source and Fiber in EDFA using Mutually Pumped Phase Conjugate Mirrors”, Technical Digest of International Quantum Electronics Conference and the ・・・　　　　　　　　　　　　　　　
2005
Kaseda, H., Okamoto, A., Y. Takayama and Kato, H.: “Improvement of Coupling Efficiency between Pump Light Source and Fiber in EDFA using Mutually Pumped Phase Conjugate Mirrors”, Technical Digest of International Quantum Electronics Conference and the Pacific Rim Conference on Lasers and Elector-Optics 2005 (IQEC and CLEO-PR2005), no. CThC3-P19(2005)＊*

Harasaka, K., Okamoto, A., Bunsen, M. and Yamamoto, M.: “Photorefractive Connection Module with Organic Photorefractive Polymer PATPD”, Technical Digest of International Quantum Electronics Conference and the Pacific Rim Conference on Lasers and Electo・・・　　　　　　　　　　　　　　　
2005
Harasaka, K., Okamoto, A., Bunsen, M. and Yamamoto, M.: “Photorefractive Connection Module with Organic Photorefractive Polymer PATPD”, Technical Digest of International Quantum Electronics Conference and the Pacific Rim Conference on Lasers and Elector-Optics 2005 (IQEC and CLEO-PR2005), no.CthC3-P21(2005)＊*

Muranaka, H., Okamoto, A., Uemura, S., Bunsen, M., and Nishio, A.: “Optical Image Cross Connector with Multiple-layered Photorefractive Polymers”, Technical Digest of International Quantum Electronics Conference and the Pacific Rim Conference on Lasers・・・　　　　　　　　　　　　　　　
2005
Muranaka, H., Okamoto, A., Uemura, S., Bunsen, M., and Nishio, A.: “Optical Image Cross Connector with Multiple-layered Photorefractive Polymers”, Technical Digest of International Quantum Electronics Conference and the Pacific Rim Conference on Lasers and Elector-Optics 2005 (IQEC and CLEO-PR2005), no.CThC3-P20(2005)＊*

Nihei, H. and Okamoto, A.: “Coherent control of a qubit embedded in photonic crystals using a dark line in emission spectra”, Proceedings of 12th European Conference on Integrated Optics (ECIO’05) , pp.598 (2005)＊*　　　　　　　　　　　　　　　
2005

Sano, T., Okamoto, A., Sato, K. and Bunsen, M.: “Selective erasure for multiplexed holograms by using photorefractive phase-shift”, The European Conference on Lasers and Electro-Optics (CLEO Europe 2005), CC-2-WED (2005)＊*　　　　　　　　　　　　　　　
2005

Ito, T. and Okamoto, A.: “Spatial spread-spectrum multiplexing for holographic data storage using random diffuser and circular spatial filter”, The European Conference on Lasers and Electro-Optics (CLEO Europe 2005), CC1-4-TUE(2005)＊*　　　　　　　　　　　　　　　
2005

Harasaka, K., Okamoto, A., Bunsen, M., and Yamamoto, M.: “Experiment on signal extraction in photorefractive connection module with organic polymer PATPD”, Proceedings of. SPIE(ISOT2005), Vol. 6050-0V(2005)＊*　　　　　　　　　　　　　　　
2005

Moritake, K., Okamoto, A., Funakoshi, H. and Ito, T.: “Security improvement with multiplexing for optical encryption based on cross-correlation of random phase masks”, Technical Digest of International Quantum Electronics Conference and the Pacific Ri・・・　　　　　　　　　　　　　　　
2005
Moritake, K., Okamoto, A., Funakoshi, H. and Ito, T.: “Security improvement with multiplexing for optical encryption based on cross-correlation of random phase masks”, Technical Digest of International Quantum Electronics Conference and the Pacific Rim Conference on Lasers and Elector-Optics 2005 (IQEC and CLEO-PR2005), no.CTuN1-2(2005)＊*

Sano, T., Okamoto, A., Sato, K. and Bunsen, M.: “Selective erasure for multiplexed holograms in photorefractive crystal using phase conjugate mirror”, Proceedings of SPIE(ISOT2005) vol.6050-0X, (2005)＊*　　　　　　　　　　　　　　　
2005

Okamoto, A., Funakoshi, H., Bunsen, M., Ito, T. and Sato, K.: “Optical security switch based on spatially phase matching in photorefractive media”, The European Conference on Lasers and Electro-Optics (CLEO Europe 2005), CC-2-WED(2005)＊*　　　　　　　　　　　　　　　
2005

Ito, T. and Okamoto, A.: “Volume holographic recording with spatial spread-spectrum multiplexing technique”, Technical Digest of International Symposium on Optical Memory and Optical Data Storage Topical Meeting 2005 (ISOM/ODS2005), no.MP-20(2005)＊*　　　　　　　　　　　　　　　
2005

Nihei, H. and Okamoto, A.: “Optical switching of an atomic system in photonic crystals using a dark line in emission spectra”, Technical Digest of Optoelectronics and Communications Conference (OECC2005), pp. 294-295(2005)＊*　　　　　　　　　　　　　　　
2005

Bunsen, M., Okamoto, A. and Furuta, H.: “A method for selective erasure of multiplexed holograms by use of double Mach-Zehnder interferometer”, Technical Digest of 10th Optoelectronics and Communications Conference (OECC2005), pp.624-625 (2005)＊*　　　　　　　　　　　　　　　
2005

Shiratori, T., Okamoto, A., Kori, K., and Funakoshi, H.: “All-optical Reconfigurable Waveguide with Mutually-pumped Phase Conjugate Mirrors for Free-space Optical Interconnection”, Technical Digest of 10th Optoelectronics and Communications Conference ・・・　　　　　　　　　　　　　　　
2005
Shiratori, T., Okamoto, A., Kori, K., and Funakoshi, H.: “All-optical Reconfigurable Waveguide with Mutually-pumped Phase Conjugate Mirrors for Free-space Optical Interconnection”, Technical Digest of 10th Optoelectronics and Communications Conference (OECC2005), no.7P-032(2005)＊*

Muranaka, H., Okamoto, A., Uemura, S., Bunsen, M., and Nishio, A.: “Optically Controlled Image Cross Connector with Photorefractive Polymer”, Technical Digest of 10th Optoelectronics and Communications Conference (OECC2005), no.7P-118(2005)＊*　　　　　　　　　　　　　　　
2005

Honma, S., Matsuyama, D., Ito, T., Okamoto, A., and Muto, S.: “Optical interconnection by holographic router and movement with orthogonal phase matrix pattern”, Technical Digest of 10th Optoelectronics and Communications Conference (OECC2005), no.6E4-7・・・　　　　　　　　　　　　　　　
2005
Honma, S., Matsuyama, D., Ito, T., Okamoto, A., and Muto, S.: “Optical interconnection by holographic router and movement with orthogonal phase matrix pattern”, Technical Digest of 10th Optoelectronics and Communications Conference (OECC2005), no.6E4-7(2005)＊*

Ito, T., Okamoto, A., and Funakoshi, H.: “Static holographic random access memory using two photorefractive crystals”, Technical Digest of 10th Optoelectronics and Communications Conference (OECC2005), no.7P-069(2005)＊*　　　　　　　　　　　　　　　
2005

Kaseda, H., Okamoto, A., Takayama, Y., Kato, H. and Sato, K.: “Effective coupling method between pump light source and fiber in EDFA with one mutually pumped phase conjugate mirror”, Technical Digest of 10th Optoelectronics and Communications Conferenc・・・　　　　　　　　　　　　　　　
2005
Kaseda, H., Okamoto, A., Takayama, Y., Kato, H. and Sato, K.: “Effective coupling method between pump light source and fiber in EDFA with one mutually pumped phase conjugate mirror”, Technical Digest of 10th Optoelectronics and Communications Conference (OECC2005), no.7P-055(2005)＊*

Okamoto, A., Terumasa Ito, Bunsen, M. and Takayama, Y.: “Fault tolerant function of dynamic refreshing holographic memory with shutter-less optical feedback circuit”, Journal of Modern Optics Vol. 52(17), pp.2453-2465 (2005)＊*　　　　　　　　　　　　　　　
2005

Nihei, H. and Okamoto, A. : “Coherent control of spontaneous emission near a photonic band edge using a dark line in emission spectra”, The European Conference on Lasers and Electro-Optics (CLEO Europe 2005), CK3-4(2005)＊*　　　　　　　　　　　　　　　
2005

Sano, T., Okamoto, A., Sato, K. and Bunsen, M.: “Experiment on selective erasure for multiplexed holograms by using photorefractive phase shift”, Technical Digest of International Quantum Electronics Conference and the Pacific Rim Conference on Lasers ・・・　　　　　　　　　　　　　　　
2005
Sano, T., Okamoto, A., Sato, K. and Bunsen, M.: “Experiment on selective erasure for multiplexed holograms by using photorefractive phase shift”, Technical Digest of International Quantum Electronics Conference and the Pacific Rim Conference on Lasers and Elector-Optics 2005 (IQEC and CLEO-PR2005), no.CWAB3-P89(2005)＊*

2-D Image Operation and Its Application to XOR Encryption with Photorefractive Crystal and Double Mach-Zehnder Interferometer
BUNSEN Masatoshi, OKAMOTO Atsushi, SATO Kunihiro, The transactions of the Institute of Electronics, Information and Communication Engineers. C, vol.J88-C, 1, 72, 73, 2005
フォトリフラクティブ結晶と二重マッハツェンダ干渉光学系による二次元画像演算を応用し,ホログラフィックメモリ中の記録データを光学的にXOR暗号化する手法を提案する.多重記録された複数のホログラムをそれぞれ独立に暗号化,復号化できることを実験により示す., The Institute of Electronics, Information and Communication Engineers, Japanese

Bunsen, M. and Okamoto, A.: “Theoretical and experimental studies of hologram multiplexing that uses a random wave front generated by photorefractive beam fanning”, Applied Optics, Vol.44(8), pp.1454-1463 (2005)＊*　　　　　　　　　　　　　　　
2005

Funakoshi, H., Okamoto, A. and Sato, K.: “Long-term reading experiment on photorefractive holographic memory with hologram sustainment technique by optical feedback”, Journal of Modern Optics, Vol. 52(11), pp. 1511-1527 (2005)＊*　　　　　　　　　　　　　　　
2005

Hologram multiplexing with photorefractive beam-fanning speckle
M Bunsen, A Okamoto, Y Takayama, OPTICS COMMUNICATIONS, 235, 1-3, 41, 47, May 2004
We propose a hologram multiplexing method with a speckled reference beam generated by the photorefractive beam-fanning effect. In this method, a bulk photorefractive crystal takes the role of generating various speckle fields as well as storing holograms. The speckle field of a reference beam used for holographic recording is generated by the photorefractive beam-fanning effect in the storage crystal. This speckle field can be changed by varying the spatial intensity distribution, the spatial phase distribution, the incident angle or the incident position of the original reference beam at the crystal surface. We experimentally demonstrate hologram multiplexing and retrieving with the speckled reference beams generated by the beam-fanning effect in a photorefractive BaTiO3 crystal. Here we vary the speckle field by changing the incident position of the original reference beam. We can successfully reconstruct stored images from four multiplexed holograms with the reference beams speckled by the beam-fanning effect. This method has the great possibility for all-optical control of hologram multiplexing, besides the simplification of an optical system compared with conventional speckle multiplexing methods using external diffusers such as ground glass and multimode optical fiber. (C) 2004 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, English

Optical manipulation of multiple stable states in photorefractive four-wave mixing
Y Takayama, A Okamoto, JOURNAL OF MODERN OPTICS, 51, 2, 197, 208, Jan. 2004
We propose an approach to manipulate the convergence in multiple solutions of phase conjugate reflectivity in photorefractive four-wave mixing. Although a method forcibly adding a pi-phase shift to an incident beam has been already proposed to control the reflectivity, some restrictions have been required in the boundary conditions for the successful operation. Here, we control the reflectivity with the boundary conditions in which the phase shift operation is ineffective by itself. In our method, the phase shift operation is combined with the procedure of turning an incident beam on and off. With a numerical analysis of four-wave mixing, we show that our new approach brings drastic change in the spatial distribution of the index grating and leads the phase conjugate reflectivity which was not manipulated previously., TAYLOR & FRANCIS LTD, English

Uemura, S., Okamoto, A. and Honma, S.: “All-optical interconnection with cross-polarized double phase conjugate mirror” Proceedings of SPIE, 5350 (Photonics West 2004): 234-242(2004).*　　　　　　　　　　　　　　　
2004

Bunsen, M., Okamoto, A. and Sato, K. :“Photorefractive holographic memory by use of beam-fanning phenomenon in storage crystal” Proceedings of 10th Microoptics Conference (MOC’04), no.F-31:CD-ROM(2004).*　　　　　　　　　　　　　　　
2004

T. Ito, Okamoto, A. and Sato, K. :“Compact dynamic holographic storage system using parallel phase-conjugate refreshment for multiplexed holograms” Proceedings of 10th Microoptics Conference (MOC’04), no.F-32:CD-ROM(2004).*　　　　　　　　　　　　　　　
2004

Okamoto, A., Funakoshi, H., Moritake, K. and Bunsen, M. :“Security measures in optical devices by spatial phase matching in a photorefractive crystal” Proceedings of 10th Microoptics Conference (MOC’04), no.F-38:CD-ROM(2004).*　　　　　　　　　　　　　　　
2004

Nihei, H. and Okamoto, A.:“Optical quantum gate using a qubit embedded in photonic bandgap structures”, 10th Microoptics Conference (MOC), H-3:CD-ROM(2004).*　　　　　　　　　　　　　　　
2004

H. Nihei and Okamoto, A.: “Coherent control of a qubit embedded in photonic bandgap structures with high-speed switching,” Proceedings of 30th European Conference on Optical Communication (ECOC2004), 5:78-79(2004).*　　　　　　　　　　　　　　　
2004

Funakoshi, H., Okamoto, A. and Sato, K.: “Long-term retrieving experiment on rewritable holographic memory with dynamic refreshment by mutual-pumped phase conjugator,” Proceedings of SPIE, 5636-93 (2004).*　　　　　　　　　　　　　　　
2004

Honma, S., Muto, S. and Okamoto, A.: “All-optical interconnection with mutually pumped four-wave mixing and optimization for high-connection efficiency,” Proceedings of SPIE, 5636-108(2004).*　　　　　　　　　　　　　　　
2004

Kori, K., Okamoto, A., Takayama, Y., Bunsen, M., Funakoshi, H. and Ito, T.: “Photorefractive bi-directional connection module with mutual-pumped phase conjugate mirror,” Proceedings of SPIE, 5642-86(2004).*　　　　　　　　　　　　　　　
2004

Ito, T., Okamoto, A. and Funakoshi, H. :“Noise Reduced Refreshment for Dynamic Holographic Memory with Phase Conjugation in a BaTiO3 Crystal,” Proceedings of 9th Optoelectronics and Communications Conference / 3rd International Conference on Optical In・・・　　　　　　　　　　　　　　　
2004
Ito, T., Okamoto, A. and Funakoshi, H. :“Noise Reduced Refreshment for Dynamic Holographic Memory with Phase Conjugation in a BaTiO3 Crystal,” Proceedings of 9th Optoelectronics and Communications Conference / 3rd International Conference on Optical Internet (OECC/COIN2004), no.16E2-2: 872-873(2004).*

Mita, A., Okamoto, A. and Funakoshi, H.: “Effect of random phase mask on input plane in photorefractive authentic memory with two-wave encryption method,” Proceedings of SPIE, 5362 (Photonics West 2004): 61-68(2004).*　　　　　　　　　　　　　　　
2004

Bunsen, M., Okamoto, A. and Takayama, Y.: “Hologram multiplexing with photorefractive beam-fanning speckle,” Opt. Commun., 235(1-3):41-47(2004).*　　　　　　　　　　　　　　　
2004

「ホトリフラクティブ相互励起型4波混合」　　　　　　　　　　　　　　　
電子情報通信学会論文誌C, VOL.J87-C, 3, 350, 351, 2004

Nihei, H. and Okamoto, A.: “Spontaneous emission from a three-level atom embedded in anisotropic photonic band gap structures”, Journal of Modern Optics, 51(13):1983-1998 (2004).*　　　　　　　　　　　　　　　
2004

「2重マッハツェンダ－干渉光学系によるスペックル多重ホログラムの選択的消去・更新手法」　　　　　　　　　　　　　　　
電子情報通信学会論文誌C, J87-C, 11, 982, 983, 2004

Kato, H., Okamoto, A. and Bunsen, M.: “Stabilization of Signal Beam Intensity for Fault-Tolerant Automatic Routing with Double Phase Conjugate Mirrors,” Proceedings of SPIE, 5363 (Photonics West 2004):148-155(2004).*　　　　　　　　　　　　　　　
2004

Yagai, T., Okamoto, A., Bunsen, M.: “All-optical interconnection with photorefractive grating array for wavelength divided multiplexing signal,” Proceedings of SPIE,5350 (Photonics West 2004): 81-88(2004).*　　　　　　　　　　　　　　　
2004

Hondo, S., Okamoto, A. and Honma, S.: “All-optical bidirectional interconnection by light-induced waveguide with double mutual-pumped phase conjugation” Proceedings of SPIE, 5363 (Photonics West 2004): 156-163(2004).*　　　　　　　　　　　　　　　
2004

Funakoshi, H. and Okamoto, A.: “Noise reduction in photorefractive memory by double mutually pumped phase conjugate mirrors” Proceedings of SPIE, 5362 (Photonics West 2004): 99-106(2004).*　　　　　　　　　　　　　　　
2004

Bunsen, M. and Okamoto, A.: “Hologram multiplexing method with photorefractive beam-fanning speckle,” Proceedings of SPIE,5362 (Photonics West 2004):128-135(2004).*　　　　　　　　　　　　　　　
2004

Takayama, Y. and Okamoto, A., “Optical manipulation of multiple stable states in photorefractive four-wave mixing,” Journal of Modern Optics, 51(2): 197-208 (2004).*　　　　　　　　　　　　　　　
2004

Kori, K., Okamoto, A., Takayama, Y. and Bunsen, M.: “All-optical Free-space Board to Board Interconnection with Photorefractive Bi-directional Connection Module,” Proceedings of 9th Optoelectronics and Communications Conference / 3rd International Conf・・・　　　　　　　　　　　　　　　
2004
Kori, K., Okamoto, A., Takayama, Y. and Bunsen, M.: “All-optical Free-space Board to Board Interconnection with Photorefractive Bi-directional Connection Module,” Proceedings of 9th Optoelectronics and Communications Conference / 3rd International Conference on Optical Internet (OECC/COIN2004), no.13P-46:204-205(2004).*

Funakoshi, H. and Okamoto, A.: “Digital Recording with Dynamic Refreshing Technique by Mutually Pumped Phase Conjugator in Photorefractive Memory,” Proceedings of Optics in Computing 2004:pp.63-64(2004).*　　　　　　　　　　　　　　　
2004

Nihei, H. and Okamoto, A.:”All-optical rotation gates using an atom embedded in photonic bandgap structures”, Proceedings of Optics in Computing: 151-152(2004).*　　　　　　　　　　　　　　　
2004

Hondo, S., Okamoto, A. and Honma, S.: “All-Optical Bi-Directional Interconnection with Double Mutual-Pumped Phase Conjugators by using Cross-Polarized Control Beam,” Proceedings of. Optics in Computing 2004:59-60(2004).*　　　　　　　　　　　　　　　
2004

Moritake, K., Okamoto, A., Mita, A. and Funakoshi, H.:“Security Enhancement of Authentic Memory by Two-Wave Encryption Method with High Resolution Phase Mask,” Proceedings of Optics in Computing 2004:53-54(2004).*　　　　　　　　　　　　　　　
2004

Bunsen, M. and Okamoto, A.: “Hologram multiplexing method with random wavefront generated by photorefractive beam-fanning effect,” Proceedings of Optics in Computing 2004:129-130(2004).*
2004

Ito, T., Okamoto, A., Funakoshi, H.: “Experiment on two-dimensional data restoring in fault-tolerant holographic memory” Proceedings of SPIE, 5362(Photonics West 2004): 111-118(2004).*　　　　　　　　　　　　　　　
2004

Okamoto, A., Bunsen, M. and Funakoshi, H.: “Rewritable Holographic Memory using All-Optical Multiplexing and Nondestructive Reading Technology,” Proceedings of 9th Optoelectronics and Communications Conference / 3rd International Conference on Optical ・・・　　　　　　　　　　　　　　　
2004
Okamoto, A., Bunsen, M. and Funakoshi, H.: “Rewritable Holographic Memory using All-Optical Multiplexing and Nondestructive Reading Technology,” Proceedings of 9th Optoelectronics and Communications Conference / 3rd International Conference on Optical Internet (OECC/COIN2004), no.13P-110: 330-331(2004).*

Experiment on Hologram Multiplexing with Random Wavefront Generated by Photorefractive Beam-Fanning Effect
BUNSEN Masatoshi, OKAMOTO Atsushi, The transactions of the Institute of Electronics, Information and Communication Engineers. C, J87-C, 1, 182, 183, 2004
書換え可能なホログラム媒質であるホトリフラクティブ結晶において, その大きな非線形性により入射光波が結晶のc軸方向へ強く散乱するビームファニング現象が発生する. この現象により記録媒質内部で生成されるランダム波面を参照光としてホログラムを多重記録する手法を新たに提案し, 実験によりその基礎動作を確認する., The Institute of Electronics, Information and Communication Engineers, Japanese

Yagai, T., Okamoto, A. and Bunsen, M., “All-optical wavelength demultiplexer with photorefractive grating array”: Proceedings of SPIE, 5646-47(2004).*　　　　　　　　　　　　　　　
2004

Hondo, S., Okamoto, A., Sato, K. and Honma, S.: “Experiment on all-optical bi-directional interconnection with double mutual pumped phase conjugate mirrors,” Proceedings of SPIE, 5644-85 (2004).*　　　　　　　　　　　　　　　
2004

Okamoto, A., Funakoshi, H., Bunsen, M. and Nishio, A: “Optical controlled matrix switch and free-space interconnection by photorefractive polymers,” Proceedings of SPIE, 5642-109 (2004).*　　　　　　　　　　　　　　　
2004

Analysis of basic operation in photorefractive authentication memory with two-wave encryption method in volume hologram
Mita Akifumi, Okamoto Atsushi, Funakoshi Hisatoshi, Proceedings of the IEICE General Conference, 2003, 1, 302, 302, 03 Mar. 2003
The Institute of Electronics, Information and Communication Engineers, Japanese

“自己励起型位相共役鏡の位相補正作用を用いたフォトリフラクティブメモリにおける画像再生実験”　　　　　　　　　　　　　　　
電子情報通信学会論文誌 C, J86-C, 12, 1360, 1361, 2003

“自由空間光通信におけるフォールトトレラント全光通信路自動切換手法”　　　　　　　　　　　　　　　
電子情報通信学会論文誌 C, J86-C, 11, 1223, 1226, 2003

“二つのホトリフラクティブ結晶を用いたフォールトトレラントホログラフィックメモリ”　　　　　　　　　　　　　　　
電子情報通信学会論文誌 C, J86-C, 11, 1143, 1150, 2003

“フォトニック結晶を用いた光メモリからの量子情報検出”　　　　　　　　　　　　　　　
電子情報通信学会論文誌 C, J86-C, 9, 997, 1006, 2003

”フォトリフラクティブメモリにおける光フィードバック回路を用いた全光学的非破壊再生手法”　　　　　　　　　　　　　　　
電子情報通信学会論文誌 C, J86-C, 3, 236, 243, 2003

Satoshi Honma and Atsushi Okamoto: “All-optical interconnection device with photorefractive semi-linear resonator ”, IEICE Trans. Electron., vol.E86-C, no.10, pp.2103-2110 (2003-10).*　　　　　　　　　　　　　　　
2003

M. Bunsen and A. Okamoto, “Experiment on hologram multiplexing with photorefractive beam-fanning speckle,” Proc. 5th International Conference on Transparent Optical Networks, no.Tu.P.8, pp.287-290, June 2003.*　　　　　　　　　　　　　　　
2003

H. Funakoshi, A. Okamoto and K. Sato, “Experiment on long-term image reading in photorefractive memory with double mutually pumped phase conjugate mirrors,” Proc. 5th International Conference on Transparent Optical Networks, no.Tu.P.9, pp.291-294, June・・・　　　　　　　　　　　　　　　
2003
H. Funakoshi, A. Okamoto and K. Sato, “Experiment on long-term image reading in photorefractive memory with double mutually pumped phase conjugate mirrors,” Proc. 5th International Conference on Transparent Optical Networks, no.Tu.P.9, pp.291-294, June 2003.*

H. Kato, A. Okamoto and M. Bunsen, “Fault-tolerant automatic routing method with two photorefractive double phase conjugate mirrors,” Proc. 5th International Conference on Transparent Optical Networks, no.Tu.P.10, pp.295-298, June 2003.*　　　　　　　　　　　　　　　
2003

Hiroyuki Nihei and Atsushi Okamoto：”Two-qubit operation of two atoms embedded in photonic crystals for optical quantum computing,” Proc. 5th International Conference on Transparent Optical Networks, no.Th.C.6, pp.212-215, June 2003.*　　　　　　　　　　　　　　　
2003

T. Yagai, A. Okamoto K. Sato and M. Bunsen, “All-optical interconnection with photorefractive cross-polarized four-wave mixing and control beam,” Proc. 9th Microoptics Conference, no.H12, pp.170-173, Oct. 2003.*　　　　　　　　　　　　　　　
2003

S. Hondo, A. Okamoto, S. Honma and H. Funakoshi, “All-optical bi-directional interconnection with double mutual-pumped phase conjugation,” Proc. 9th Microoptics Conference, no.H13, pp.174-177, Oct. 2003.*　　　　　　　　　　　　　　　
2003

H. Kato, A. Okamoto and M. Bunsen, “Fault-tolerant automatic routing method with photorefractive double phase conjugate mirrors,” Proc. 9th Microoptics Conference, no.H14, pp.178-181, Tokyo, Japan, Oct. 2003.*　　　　　　　　　　　　　　　
2003

H. Funakoshi, A. Okamoto and K. Sato, “Dynamic Refreshing Technique in Photorefractive Memory with Mutually Pumped and Self-Pumped Phase Conjugate Mirrors,” Proc. International Symposium on Optical Memory (ISOM2003), no.We-F-27, pp.122-123, Nov. 2003.*　　　　　　　　　　　　　　　
2003

M. Bunsen and A. Okamoto “Speckle-Multiplexed Holographic Memory with Photorefractive Beam-fanning Effect,” Proc. International Symposium on Optical Memory (ISOM2003), no.We-F-57, pp.184-185, Nov. 2003.*　　　　　　　　　　　　　　　
2003

A. Mita and A. Okamoto “High Robustness against Unlawful Access in Photorefractive Authentic Memory with Two-wave Encryption Method,” Proc. International Symposium on Optical Memory (ISOM2003), no.We-F-67, pp.204-205, Nov. 2003.*　　　　　　　　　　　　　　　
2003

T. Ito, A. Okamoto, S. Homma and M. Toishi “All-optical Data Restoring Method for Photorefractive Holographic Memory,” Proc. International Symposium on Optical Memory (ISOM2003), no.Th-H-05, pp.242-243, Nara, Japan, Nov. 2003.*　　　　　　　　　　　　　　　
2003

Hiroyuki Nihei and Atsushi Okamoto：”THz emission from a multifunctional active atomic device in photonic crystals,” IEEE LEOS, 5th Pacific Rim Conference on Lasers and Electro-Optics (CLEO/PR), WP-(16)-3, December 2003.*　　　　　　　　　　　　　　　
2003

S. Uemura, A. Okamoto and S. Honma, “All-optical auto-tracking by bi-directional connection switch with cross polarized DPCM,” Proc. 9th Microoptics Conference, no.H15, pp.182-185, Oct. 2003.*　　　　　　　　　　　　　　　
2003

「電子デバイスの基礎」<桜庭一郎，岡本 淳>　　　　　　　　　　　　　　　
森北出版, 2003

Spontaneous emission from a three-level atom placed in three-dimensional photonic crystals in the long-time limit
Hiroyuki Nihei, Atsushi Okamoto, Journal of Modern Optics, 49, 9, 1463, 1477, 20 Jul. 2002
The paper describes the spontaneous emission from a three-level atom placed in a periodic dielectric microstructure which exhibits a complete three-dimensional photonic band gap. By using the Euler approach, the upper level population of the atom is calculated for a wide range of relationships between the Rabi frequency and the detuning of the atomic transition frequency from the upper band edge. The results indicate that there are three cases of the relationship between Rabi frequency and detuning, which determine distinctive states of the atomic population in the long-time limit. When the detuning is greater than the Rabi frequency, the upper level has a zero steady-state atomic population, which leads to enhancement of spontaneous emission. When the magnitude of the detuning is less than the Rabi frequency, the upper level has a nonzero steady-state atomic population, which leads to suppression of spontaneous emission. When the negative detuning is greater than the Rabi frequency, the upper level has a nondecaying oscillatory-state atomic population due to long-time atomic splitting. These three properties of the spontaneous emission are relevant to several optical devices on an atomic scale, such as optical memories, switches and clocks., English

”ホトリフラクティブ相互励起型位相共役現象と結晶端面を利用したセミリニア共振器を用いた全光インタコネクション”　　　　　　　　　　　　　　　
電子情報通信学会論文誌 C, J85-C, 5, 402, 403, 2002

Experiment on Channel Branching in PRCM with Spatial Multiplexed Image
NOMURA Junichi, OKAMOTO Atsushi, SATO Kunihiro, NAKATOGAWA Takahiko, The Transactions of the Institute of Electronics,Information and Communication Engineers. C, J85-C, 1, 35, 37, 2002
光増幅・分岐機能を兼ね備えたPRCMにおいて, 水平方向に並列化した光信号のチャネル分岐を行うために消去光を用いる手法を提案する.空間並列化された画像情報から, 制御光の操作により望みのチャネルの情報のみの分岐が可能であることを実験的に示す., The Institute of Electronics, Information and Communication Engineers, Japanese

Mitsuru Toishi, Atsushi Okamoto, Kunihiro Sato:“Experiment on Image Data Restoring in All-Optical Fault-tolerant Holographic Memory”, Seventh Optoelectronics and Communications Conference (OECC 2002) Technical Digest, 10P-80, pp346-347(2002).*　　　　　　　　　　　　　　　
2002

Hisatoshi Funakoshi, Atsushi Okamoto and Kunihiro Sato: “Wavelength-Multiplexed Photorefractive Memory with Nondestructive Reading/Writing Technique”, Optics in Computing 2002 (OC2002), OTuD5, pp.132-134 (2002).*　　　　　　　　　　　　　　　
2002

Satoshi Honma and Atsushi Okamoto: “Experiment on all-optical interconnection with photorefractive semi-linear resonator”, Optics in Computing 2002 (OC2002), OTuD3, pp.126-128 (2002).*　　　　　　　　　　　　　　　
2002

Toshiya Kaino, Atsushi Okamoto and Satoshi Honma: “Fault Tolerant All-optical Router by Using Two All-optical Switches with Photorefractive Two-wave Mixing”, Optics in Computing 2002 (OC2002), OTuD2, pp.123-125 (2002).*　　　　　　　　　　　　　　　
2002

Hiroyuki Nihei and Atsushi Okamoto: “Rotation Gate Operation in an Atomic System within Photonic Crystals for Quantum Computing”, Optics in Computing 2002 (OC2002), OTuA3, pp.68-70 (2002).*　　　　　　　　　　　　　　　
2002

Tohru Hasegawa, Atsushi Okamoto, Takahiko Nakatagawa and Kunihiro Sato: “Experiment on Reconfigurable Interconnection for Free Space and Wavelength Division Multiplexing System”, Optics in Computing 2002 (OC2002), OMA1, pp.1-3 (2002).*　　　　　　　　　　　　　　　
2002

Yoshihisa Takayama, Satoshi Honma, Atsushi Okamoto, “OPTICAL INVERSE FILTER FOR HOLOGRAPHIC FILTERING BY PHOTOREFRACTIVE FOUR-WAVE MIXING WITH INCOHERENT ERASURE”, Nonlinear Optics, 29, pp. 157-166(2002).*　　　　　　　　　　　　　　　
2002

”相互励起型位相共役鏡を用いた偏波により制御可能な２チャネルの全光クロスコネクションスイッチ”　　　　　　　　　　　　　　　
電子情報通信学会論文誌 C, J85-C, 10, 944, 945, 2002

Tsutomu Nakada, Atsushi Okamoto, Kunihiro Sato, “Reconfigurable free-space all-optical interconnection with beam-fanning switch in photorefractive crystal”, Optics Communications, 208, pp.69-77 (2002).*　　　　　　　　　　　　　　　
2002

Toshiya Kaino, Atsushi Okamoto, Satoshi Honma, “Fault Tolerant All-optical Router with Photorefractive All-optical Switch”, Advanced Optical Materials and Devices(AOMD2002), P28, pp. 151(2002).*　　　　　　　　　　　　　　　
2002

Tokonobu Mitasaki, Atsushi Okamoto, Satoshi Honma, “All-optical interconnection with wiring maintenance technique by integrated full-linear resonator”, Advanced Optical Materials and Devices(AOMD2002), p29, pp152(2002).*　　　　　　　　　　　　　　　
2002

Satoshi Honma, Atsushi Okamoto, “All-optical bi-directional cross-connector with photorefractive double phase conjugation and control beam”, Advanced Optical Materials and Devices(AOMD2002), p30, pp153(2002).*　　　　　　　　　　　　　　　
2002

Mitsuru Toishi, Atsushi Okamoto, Kunihiro Sato, “Dynamic Restoring Technique for Dropout Data in All-optical Fault Tolerant Holographic Memory”, Advanced Optical Materials and Devices(AOMD2002), p31, pp154(2002).*　　　　　　　　　　　　　　　
2002

Hisatoshi Funakoshi, Atsushi Okamoto, “Photorefractive Nondestructive Memory with Kitty-Type Conjugator”, Advanced Optical Materials and Devices(AOMD2002), p32, pp155(2002).*　　　　　　　　　　　　　　　
2002

Satoshi Honma, Atsushi Okamoto, “Bi-directional cross connector with double phase conjugator and polarization multiplexed control signal”, Proceedings of SPIE (Holography, Diffractive Optics, and Applications), 4924, pp.282-293(2002).*　　　　　　　　　　　　　　　
2002

Akifumi Mita, Atsushi Okamoto, Noriyasu Tsuji, Masatoshi Bunsen, “ High Performance Encryption Method and All-optical Authentic Memory with Photorefractive Crystal”, Proceedings of SPIE (Advanced Optical Storage Technology), 4930, pp. 351-358(2002).*　　　　　　　　　　　　　　　
2002

Kazumasa Kori, Atsushi Okamoto, Takahiko Nakatogawa, Kunihiro Sato, Toshiya Kaino:“Experimant on amplification of WDM and spatial multiplexed signals in Photorefractive Connection Module”, Seventh Optoelectronics and Communications Conference (OECC 200・・・　　　　　　　　　　　　　　　
2002
Kazumasa Kori, Atsushi Okamoto, Takahiko Nakatogawa, Kunihiro Sato, Toshiya Kaino:“Experimant on amplification of WDM and spatial multiplexed signals in Photorefractive Connection Module”, Seventh Optoelectronics and Communications Conference (OECC 2002) Technical Digest, 10P-16, pp218-219(2002).*

T. Hasegawa, A. Okamoto, K. Sato, and M. Toishi, “Experiment on all-optical interconnection with wavelength multiplexed signal using single cat conjugator”, 3rd International Conference on Optics-photonics Design & Fabrication(ODF2002), P27, pp.149-150・・・　　　　　　　　　　　　　　　
2002
T. Hasegawa, A. Okamoto, K. Sato, and M. Toishi, “Experiment on all-optical interconnection with wavelength multiplexed signal using single cat conjugator”, 3rd International Conference on Optics-photonics Design & Fabrication(ODF2002), P27, pp.149-150(2002).

M. Bunsen, A. Okamoto, “All optical interconnection using spatial phase-address multiplexed signal and control pattern decoder”, 3rd International Conference on Optics-photonics Design & Fabrication(ODF2002), P26, pp.147-148(2002).　　　　　　　　　　　　　　　
2002

Y. Kawata, A. Okamoto, S. Honma,“Experiment on all-optical interconnection with wavelength multiplexed signal using single cat conjugator,” 3rd International Conference on Optics-photonics Design & Fabrication(ODF2002), P28, pp.151-152(2002).　　　　　　　　　　　　　　　
2002

Masatoshi Bunsen, Atsushi Okamoto, Kunihiro Sato, “Improvement of storage density in photorefractive disk-type memory by logical multilayer recording method”, Proceedings of SPIE Proceedings of SPIE (Advanced Optical Storage Technology),4930, pp.343-35・・・　　　　　　　　　　　　　　　
2002
Masatoshi Bunsen, Atsushi Okamoto, Kunihiro Sato, “Improvement of storage density in photorefractive disk-type memory by logical multilayer recording method”, Proceedings of SPIE Proceedings of SPIE (Advanced Optical Storage Technology),4930, pp.343-350 (2002).*

Tokinobu Mitasaki, Atsushi Okamoto, Satoshi Honma:“Optical maintenance technique for dynamic hologram and its application for all-optical interconnection”, Seventh Optoelectronics and Communications Conference (OECC 2002) Technical Digest, 10P-18, pp22・・・　　　　　　　　　　　　　　　
2002
Tokinobu Mitasaki, Atsushi Okamoto, Satoshi Honma:“Optical maintenance technique for dynamic hologram and its application for all-optical interconnection”, Seventh Optoelectronics and Communications Conference (OECC 2002) Technical Digest, 10P-18, pp222-223(2002).*

Tohru Hasegawa, Atsushi Okamoto, Takahiko Nakatogawa, Kunihiro Sato:“Performance enhancement for all-optical interconnection with WDM signals in photorefractive crystal”, Seventh Optoelectronics and Communications Conference (OECC 2002) Technical Diges・・・　　　　　　　　　　　　　　　
2002
Tohru Hasegawa, Atsushi Okamoto, Takahiko Nakatogawa, Kunihiro Sato:“Performance enhancement for all-optical interconnection with WDM signals in photorefractive crystal”, Seventh Optoelectronics and Communications Conference (OECC 2002) Technical Digest, 10P-17, pp220-221(2002).*

Toshiya Kaino, Atsushi Okamoto, Satoshi Honma:“Swicthing Property of Fault Tolerant All-Optical Router by Using Two All-optical switch with Photorefractive Two-Wave Mixing”, Seventh Optoelectronics and Communications Conference (OECC 2002) Technical Di・・・　　　　　　　　　　　　　　　
2002
Toshiya Kaino, Atsushi Okamoto, Satoshi Honma:“Swicthing Property of Fault Tolerant All-Optical Router by Using Two All-optical switch with Photorefractive Two-Wave Mixing”, Seventh Optoelectronics and Communications Conference (OECC 2002) Technical Digest, 10A3-7, pp102-103(2002).*

Study on image restoration by photorefractive effect
TAKAYAMA Yoshihisa, OKAMOTO Atsushi, ARAKI Kenichi, Technical report of IEICE. OPE, 100, 639, 37, 42, 16 Feb. 2001
A method for image restoration by photorefractive effect is studied.The already proposed methos have respective features;(1)the real-time image restoration is performed but the position to obtain the restored image is different from of the distorted image, or(2)the receive positions of the distorted and restored images are almost the same but it is far from the real-time process.To restore the image at the receive position of the distorted image, we connects the photorefractive four-wave mixing and the holographic filtering technique, where the blur function of the distorted image is introduced into the four-wave mixing process as the erase beam., The Institute of Electronics, Information and Communication Engineers, Japanese

Photorefractive four-wave mixing for optical image restoration
Yoshihisa Takayama, Atsushi Okamoto, Kenichi Araki, Proceedings of SPIE - The International Society for Optical Engineering, 4353, 247, 255, 01 Jan. 2001
We describe an optical image restoration by using holographic filtering and photorefractive four-wave mixing. A beam generated by four-wave mixing, that is, the phase conjugate beam, reads a hologram recorded by a blurred image and blur function, where the four-wave mixing process is influenced by an erase beam which has the information of the blur function. We calculate the generation efficiency of the phase conjugate beam and show that the amplitude of the phase conjugate beam can be inversely proportional to the intensity of the erase beam. We also simulate the image restoration by preparing sample images and show that the blur effect can be removed from the distorted image by this method.

Three-dimensional analysis of code processing in photorefractive holographic memory
Noriyasu Tsuji, Atsushi Okamoto, Yoshihisa Takayama, Takahiko Nakatogawa, Proceedings of SPIE - The International Society for Optical Engineering, 4598, 233, 240, 01 Jan. 2001
We have proposed an all-optical memory with authentication and unlawful access detection using photorefractive four-wave mixing. If the data is read out by the reading beam with the improper key, the output intensity is scarcely zero and any output isn't obtained. Therefore we can judge at a glance whether or not the used decoding key is the proper key. We analyze the diffraction efficiency with consideration of the phase mismatching to evaluate the fidelity of the hologram. In this analysis, we examine the property of the crystal that depends on three-dimensional coupling coefficient. We simulate the encoding and decoding process with some image data in this all-optical memory with authentication and unlawful access detection. We show that the encoded image is restored to its original image in case of retrieving with the proper key, on the other hand the retrieved image of which intensity is scarcely zero is obtained in case of retrieving with the improper key.

「交差偏光４波混合を用いたホトリフラクティブディスクタイプメモリにおける多重記録特性の解析及び実験」　　　　　　　　　　　　　　　
電子情報通信学会論文誌 C, J84-C, 11, 1083, 1089, 2001

「フォトリフラクティブ2波混合と制御光を用いた全光インタコネクション」　　　　　　　　　　　　　　　
電子情報通信学会論文誌 C, J84-C, 9, 900, 901, 2001

「光学的インバースフィルタへのフォトリフラクティブ４波混合の適用」　　　　　　　　　　　　　　　
電子情報通信学会論文誌 C, J84-C, No.3, 222, 223, 2001

Tokinobu Mitasaki, Atsushi Okamoto, Satoshi Honma: “All-optical interconnection and routing memory by photorefractive full-linear resonator”, 8th Microoptics Conference, MOC’01, H25, pp.226-229(2001-10).*　　　　　　　　　　　　　　　
2001

Tokinobu Mitasaki, Atsushi Okamoto and Satoshi Honma: “All-optical interconnection with pattern memory function by photorefractive full-linear resonator”, Proceedings of SPIE (ISPA 2001), Vol.4598-33, pp.225-232, (2001-11).*　　　　　　　　　　　　　　　
2001

Hiroyuki Nihei and Atsushi Okamoto: “All-optical switching scheme using a three-level atomic system within photonic crystals”, Proceedings of SPIE (ISPA 2001), Vol.4598-31, pp.217-224,(2001-11).*　　　　　　　　　　　　　　　
2001

Noriyasu Tsuji, Atsushi Okamoto, Yoshihisa Takayama and Takahiko Nakatogawa: ”Three-dimensional analysis of code processing in photorefractive holographic memory”, Proceedings of SPIE (ISPA 2001), Vol.4598-34, pp.233-240(2001-11).*　　　　　　　　　　　　　　　
2001

Mitsuru Toishi, Atsushi Okamoto and Kunihiro Sato: “Experiment on automatic data duplication in all-optical holographic memory”, Proceedings of SPIE (ISPA 2001), Vol.4598-28, pp.200-207(2001-11).*　　　　　　　　　　　　　　　
2001

Hisatoshi Funakoshi, Atsushi Okamoto and Kunihiro Sato: “Image reading and writing experiment on photorefractive nondestructive memory”, Proceedings of SPIE (ISPA 2001), Vol.4598-27, pp.193-199(2001-11).*　　　　　　　　　　　　　　　
2001

Hiroyuki Nihei, Atsushi Okamoto: “Switching Effect of a Single Three-level Atom Within Photonic Crystals for Quantum Computation”, 8th Microoptics Conference, MOC’01, H41, pp.290-293,(2001-10).*　　　　　　　　　　　　　　　
2001

Noriyasu Tsuji, Atsushi Okamoto, Yoshihisa Takayama, Satoshi Honma: “All-optical Authentication and Unlawful Access Detection by Photorefractive Four-wave Mixing”, 8th Microoptics Conference, MOC’01, H29, pp.242-245(2001-10).*　　　　　　　　　　　　　　　
2001

Takahiko Nakatogawa, Atsushi Okamoto Kunihiro Sato: “Multi-channel reading in free space for WDM signals with photorefractive connection module”, 8th Microoptics Conference, MOC’01, H26, pp.230-233(2001-10).*　　　　　　　　　　　　　　　
2001

Satoshi Honma, Atsushi Okamoto, Yoshihisa Takayama, "Photorefractive duplex two-wave mixing and all-optical deflection switch", J. Opt. Soc. Am. B, 18(7), pp. 974-981, (2001-7).*　　　　　　　　　　　　　　　
2001

Takahiko Nakatogawa, Atsushi Okamoto, Kunihiro Sato: “Multiplicity of free space WDM system with Photorefractive Connection Module”, Conference Proceedings of OEEC/IOOC 2001, Poster Session-Stream 1-1, pp.341-343(2001-07).*　　　　　　　　　　　　　　　
2001

Satoshi Honma, Atsushi Okamoto: “All-optical interconnection by optical feedback and double phase conjugation”, Conference Digest of CLEO/Europe-EQEC Focus Meetings 2001,C-NLP 230, pp.217(2001-06).*　　　　　　　　　　　　　　　
2001

Takahiko Nakatogawa, Atsushi Okamoto, Kunihiro Sato: “Experiment on free space WDM system with Photorefractive Connection Module”, Conference Digest of CLEO/Europe-EQEC Focus Meetings 2001,C-NLP 226, pp.213(2001-06).*　　　　　　　　　　　　　　　
2001

Hiroyuki Nihei, Atsushi Okamoto: “Photonics crystal systems for high-speed optical memory device on an atomic scale”,ICOSM2001-06,Proceedings of SPIE Vol. 4416, pp.470-473(2001-06).*　　　　　　　　　　　　　　　
2001

Atsushi Okamoto, Satoshi Honma, Toshiya Kaino, Mitsuru Toishi: “Fault-tolerant system using all-optical sensing and feed back circuits”,ICOSM2001-06,Proceedings of SPIE Vol. 4416, pp.396-399(2001-06).*　　　　　　　　　　　　　　　
2001

Takayuki Kaneda, Atsushi Okamoto, Kunihiro Sato, “All-optical image cross connector and the picture distribution technology,”Optics in Computing, OSA Technical Digest, OWD2 , pp.96-98 (2001-1).*　　　　　　　　　　　　　　　
2001

Yoshiyasu Kato, Atsushi Okamoto, Kunihiro Sato, “Multi-valued phase-conjugate reflectivity controlled by rotation of the pump beam polarization,”Optics in Computing, OSA Technical Digest, OWD1 ,pp.93-95(2001-1).*　　　　　　　　　　　　　　　
2001

Toshiya Kaino, Atsushi Okamoto, Tsutomu Nakada and Takayuki Kaneda:”Fault tolerant all-optical routing device with two-wave mixng”,CLEO/Pacific Rim 2001 TECHNICAL DIGEST Volume-II,pp.256-257(2001-07).*　　　　　　　　　　　　　　　
2001

Satoshi Honma, Atsushi Okamoto: “Resonant State Switching with Photorefractive Enhanced Semi-Linear Configuration, and It’s Applications”, Conference Proceedings of OEEC/IOOC 2001, Poster Session-Stream 2-6, pp.386-398(2001-07).*　　　　　　　　　　　　　　　
2001

Atsushi Okamoto, Takahiko Nakatogawa, Tohru Hasegawa, Satoshi Honma: “All-optical Reconfigurable Interconnection for Free Space and Wavelength Division Multiplexing System”, 8th Microoptics Conference, MOC’01, H24, pp.222-225(2001-10).*　　　　　　　　　　　　　　　
2001

Hisatoshi Funakoshi, Atsushi Okamoto, Yoshihisa Takayama, Kunihiro Sato: “Thresholding Property of Nondestructive Memory with Photorefractive Crystal”, Conference Proceedings of OEEC/IOOC 2001, Poster Session-Stream 2-7, pp.389-391(2001-07).*　　　　　　　　　　　　　　　
2001

Mitsuru Toishi, Atsushi Okamoto, Satoshi Honma, Masatoshi Bunsen: “Optimization of Beam Intensities For High Efficient Fault-tolerant Holographic Memory”, Conference Proceedings of OEEC/IOOC 2001, Poster Session-Stream 2-9, pp.394-396(2001-07).*　　　　　　　　　　　　　　　
2001

Hiroyuki Nihei, Atsushi Okamoto: “Proposal of Optical Multifunctional Device Composed of an Atomic System Placed Within Photonic Crystals”, Conference Proceedings of OEEC/IOOC 2001, Poster Session-Stream 2-10, pp.397-398(2001-07).*　　　　　　　　　　　　　　　
2001

Hisatoshi Funakoshi, Atsushi Okamoto, Masatoshi Bunsen, Kunihiro Sato: “Photorefractive Nondestructive Memory with Optical Feedback Circuit”, Conference Digest of CLEO/Europe-EQEC Focus Meetings 2001,C-NLP 231, pp.218(2001-06).*　　　　　　　　　　　　　　　
2001

Mitsuru Toishi, Atsushi Okamoto, Satoshi Honma and Masatoshi Bunsen ”Fault-tolerant holographic memory with two photorefractive crystals”,CLEO/Pacific Rim 2001 TECHNICAL DIGEST Volume-II,pp.160-161(2001-07).*　　　　　　　　　　　　　　　
2001

Toshiya Kaino, Atsushi Okamoto, Yasuhiko Nakanishi, Kunihiro Sato: “Experiment of Fault Tolerant All-Optical Routing Device with two-wave mixing”, Conference Proceedings of OEEC/IOOC 2001, Poster Session-Stream 1-11, pp.363-364(2001-07).*　　　　　　　　　　　　　　　
2001

Hiroyuki Nihei and Atsushi Okamoto: “Switching Time of Optical Memory Devices Composed of Photonic Crystals with an Impurity Three-Level Atom”, Jpn. J. Appl. Phys., Vol. 40, Part 1(No. 12), pp.6835-6840 (2001-12).*　　　　　　　　　　　　　　　
2001

Analysis of optimum incident condition in all-optical interconnection by matrix switch with photorefractive two-wave mixing
NAKANISHI Yasuhiko, OKAMOTO Atsushi, HONMA Satoshi, NAKADA Tsutomu, SATO Kunihiro, Technical report of IEICE. OPE, 100, 494, 19, 24, 07 Dec. 2000
We propose an all-optical interconnection by matrix switch with the photorefractive two-wave mixing. We explain the concept of the optical interconnection and experiment on 2×2 operation. We analyze the optimum incident condition of beams by numerical analysis for the improvement of the switching performance., The Institute of Electronics, Information and Communication Engineers, Japanese

Characteristics of multiplex recording in photorefractive disk-type memory
BUNSEN Masatoshi, OKAMOTO Atsushi, SATO Kunihiro, Technical report of IEICE. OPE, 100, 494, 13, 18, 07 Dec. 2000
In this paper, we propose the disk-type memory with the photorefractive crystal. In the photorefractive memory, holograms can be multiplexed in a same spot of the crystal. Among various multiplexing method, we employ the shift multiplexing for our memory. In this method, we can angularly multiplex holograms by means of the shift of the recording position induced by the rotation of the disk. We analyze the amount of shift required for multiplexing differentiable holograms and carry out an experiment to measure the amount of shift. On the other hand, there is a problem that stored data is erased by the subsequent recordings when holograms are multiplexed. To store a grate deal of data, it is essential to balance the subsequent erasure against the initial exposure by means of recording schedule. We suggest two kinds of recording schedule for this multiplexing method, and estimate the optimum recording conditions and the generation efficiency of the output., The Institute of Electronics, Information and Communication Engineers, Japanese

Multi-valued property of phase conjugation and control of its threshold condition
Y. Kato, A. Okamoto, Y. Takayama, Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest, 159, 160, 01 Dec. 2000
Theory and application of cross-polarized four wave mixing in photorefractive crystal has attracted much attention due to its advantage of efficient utilization of multi-valued phase conjugate beam. The multi-valued property of parallel-polarized four wave mixing requires large coupling strength and according to the result the operation of the pump ratio can lower the required value of the coupling strength in cross-polarized four wave mixing.

Optical deconvolution by using photorefractive effect
TAKAYAMA Yoshihisa, OKAMOTO Atsushi, ARAKI Kenichi, Technical report of IEICE. OPE, 100, 95, 61, 66, 19 May 2000
We attempt to utilize the photorefractive effect for optical image restoration that employs the holographic filtering technique. The blur function of the distorted image is introduced in four-wave mixing process as the erase beam. The phase conjugate beam generated by the process reads the hologram. With numerical analysis, the condition in which the amplitude of the phase conjugate beam is inversely proportional to the intensity of the erase beam is determined. As a result we show the optical deconvolution is performed and the original image appears where the distortion is eliminated., The Institute of Electronics, Information and Communication Engineers, Japanese

Experiment of Channel Branching with the Spatial Multiplexed Signal on the Connection Module(PRCM)
NOMURA Junichi, OKAMOTO Atsushi, SATO Kunihiro, 電気学会研究会資料. : The Papers of Technical Meeting on Electromagnetic Theory, IEE Japan. EMT, 電磁界理論研究会, 2000, 14, 7, 12, 19 Jan. 2000
Japanese

Beam distribution of optical distributor in forward four-wave mixing
SEKINE Tomotsugu, OKAMOTO Atsushi, SATO Kunihiro, 電気学会研究会資料. : The Papers of Technical Meeting on Electromagnetic Theory, IEE Japan. EMT, 電磁界理論研究会, 2000, 14, 13, 18, 19 Jan. 2000
Japanese

Quantum fluctuation interference in the atomic population of a photonic band gap crystal
NIHEI Hiroyuki, OKAMOTO Atsushi, 電気学会研究会資料. : The Papers of Technical Meeting on Electromagnetic Theory, IEE Japan. EMT, 電磁界理論研究会, 2000, 1, 51, 56, 18 Jan. 2000
Japanese

Bistability control of phase conjugate reflectivity by erase beam in photorefractive four-wave mixing
H Okada, A Okamoto, Y Takayama, ELECTRONICS AND COMMUNICATIONS IN JAPAN PART II-ELECTRONICS, 83, 6, 8, 14, 2000
When the nonlinear effect of the crystal is strong in four-wave mixing using a photorefractive crystal, the generated phase conjugate light takes multiple values. In this paper, a new method of controlling the bistable values of the phase conjugate reflectivity, that is, the ratio of the phase conjugate beam to the probe beam, via the erase beam is proposed for use in four-wave mixing using the fanning beam generated in the crystal in place of the forward pump beam. It is extremely difficult to solve analytically the problem of four-wave mixing including the fanning beam. By means of a model in which a part of the probe beam is used for fanning and acts as the forward pump beam in the interaction region, the previous method of analysis for four-wave mixing can be used. First, a steady-state analysis of the phase conjugate reflectivity is carried out. It is shown that the phase conjugate reflectivity has bistable values as function of the intensity of the erase beam. Next, by time response analysis, the intensity of the erase beam is varied and the bistable values of the phase conjugate reflectivity are controlled. Finally, the theory is compared with experiments. (C) 2000 Scripta Technica., SCRIPTA TECHNICA-JOHN WILEY & SONS, English

Kaneda, T., Okamoto, A., Honma, S., Nakada, T., and Sato, K.: “Optical image connector with photorefractive four-wave mixing”, proceedings of 2nd International Conference on Optical Design and Fabrication (ODF2000), P27: 229-232 (2000)*　　　　　　　　　　　　　　　
2000

Nomura, J., Okamoto, A., Okada, H., Sato, K.: “Experiment on channel branching in the photorefractive connection module”, proceedings of 2nd International Conference on Optical Design and Fabrication (ODF2000), P28: 233-246 (2000)*　　　　　　　　　　　　　　　
2000

Nihei, H., Okamoto, A.: “Dynamic Phase Properties of Atomic Population on the Excited State in a Photonic Crystal”, Fifth Optoelectronics and Communications Conference (OECC 2000) Technical Digest, 12P-37: 260-261, (2000) . *　　　　　　　　　　　　　　　
2000

Okamoto, A.: “All Optical Interconnection by Photorefractive Effect and Self-Routing Application”, Optics in Computing 2000, SPIE 4089: OC2000, 939-947 (2000)*　　　　　　　　　　　　　　　
2000

Nakada, T., Okamoto, A., Sato, K.: “Experiments of reconfigurable all-optical interconnection by beam fanning switch”, Conference on Lasers and Electro-Optics (CLEO2000), TECHNICAL DIGEST, CLEO2000: 508 (2000) *　　　　　　　　　　　　　　　
2000

Kaneda, T., Okamoto, A., Sato, K., Nakada, T.: “Experiment on All-Optical Interconnection with Photorefractive Four-Wave Mixing”, Fifth Optoelectronics and Communications Conference (OECC 2000) Technical Digest, 12P-5:196-197, (2000) *　　　　　　　　　　　　　　　
2000

Kato, Y., Okamoto, A., Takayama, Y.: “Multi-valued property of phase conjugation and control of its threshold condition”, Conference on Lasers and Electro-Optics, TECHNICAL DIGEST, CLEO2000: 159-160 (2000)*　　　　　　　　　　　　　　　
2000

Nakatogawa, T., Okamoto, A., Kentaro Watanabe, Sato, K., Okada, H.: “Gain Stabilized Configuration in PRCM Circuit and Optical Bus System”, Optics in Computing 2000, SPIE 4089: OC2000, 345-350 (2000) *　　　　　　　　　　　　　　　
2000

Bunsen, M., Okamoto, A., Sato, K.: “Enhancement of storage density in photorefractive disk-type memory with cross polarized four-wave mixing”, Optics in Computing 2000, SPIE 4089: OC2000, .806-814 (2000) *　　　　　　　　　　　　　　　
2000

Honma, S., Okamoto, A., Takayama, Y.: “Optical Demodulator with Photorefractive Cross Polarized Duplex Two-Wave Mixing”, Optics in Computing 2000, SPIE 4089: OC2000, 867-875 (2000)　　　　　　　　　　　　　　　
2000

Yoshida,T., Okamoto, A., Y. Takayama, Sato, K. : “Operable conditions of the beam-fanning novelty filter for the c axis and the incident angle”, App. Opt.,39(32): 5940-5948 (2000)*　　　　　　　　　　　　　　　
2000

Funakoshi, H., Okamoto, A., Bunsen,M. and Sato, K.: “Nondestructive readout technique with photorefractive holographic memory”, proceedings of 2nd International Conference on Optical Design and Fabrication (ODF2000), P29: 237-240 (2000)*　　　　　　　　　　　　　　　
2000

Honma, S., Okamoto, A., Sato, K.: “Experiment on All-Optical Switch with Photorefractive Duplex Two-Wave Mixing”, Conference on Lasers and Electro-Optics/Europe (CLEO/Europe2000), CONFERENCE DIGEST, CtuN6: 156,(2000)*　　　　　　　　　　　　　　　
2000

Takahashi, Y., Okamoto, A., Honma, S.: “All-optical Channel Selector and Angular Resolution of KNbO3 Crystal”, Fifth Optoelectronics and Communications Conference (OECC 2000) Technical Digest, 12P-67: 320-321, ( 2000) .*　　　　　　　　　　　　　　　
2000

Nakanishi, Y., Okamoto, A., Nakada, T., Honma, S.: “All-optical interconnection by matrix switching with photorefractive two-wave mixing”, Conference on Lasers and Electro-Optics /Europe(CLEO/Europe2000), CONFERENCE DIGEST, CTuK86: 129,(2000)*　　　　　　　　　　　　　　　
2000

Bunsen, M., Okamoto, A., Sato, K.: “Optimization of multiplexing scheme in photorefractive disk-type memory”, Conference on Lasers and Electro-Optics/Europe(CLEO/Europe2000), CONFERENCE DIGEST, CtuK77: 125,(2000)*　　　　　　　　　　　　　　　
2000

Tsuji, N., Okamoto, A., Honma, S. and Bunsen, M.: “AUTHENTIC FUNCTION IN PHOTOREFRACTIVE HOLOGRAPHIC MEMORY”, International Symposium on Optical Memory (ISOM2000), Technical Digest, Fr-J-27: 160-161(2000).*　　　　　　　　　　　　　　　
2000

Nihei, H., Okamoto, A.: “Switching time of optical memory devices composed of photonic crystals”, proceedings of 2nd International Conference on Optical Design and Fabrication (ODF2000), P20: 201-204 (2000)*　　　　　　　　　　　　　　　
2000

Analysis of multi-valued property of phase-conjugate reflectivity in cross-polarized four-wave mixing
KATO Yoshiyasu, OKAMOTO Atsushi, TAKAYAMA Yoshihisa, Technical report of IEICE. OME, 99, 350, 61, 66, 13 Oct. 1999
In this report, the multi-valued property of the phase-conjugate reflectivity in cross-polarized four-wave mixing with photorefractive crystal is analyzed. First, the phase-conjugate reflectivity in cross-polarized four-wave mixing is derived by using the grating-integral method, and its property is analyzed. We show that multi-valued property of phase-conjugate reflectivity is appeared when the coupling strength is efficiently strong. In addition, multi-valued property in cross-polarized four-wave mixing for probe ratios and pump ratios is also discussed., The Institute of Electronics, Information and Communication Engineers, Japanese

ホトリフラクティブ多重2波混合における定常および時間応答解析
本間 聡, 岡本 淳, 高山 佳久, 電子情報通信学会技術研究報告, 99, 351, 55, 60, 13 Oct. 1999
電子情報通信学会, Japanese

Concept of photorefractive connection module by photorefractive four-wave mixing with extraordinary writing beams and an ordinary reading beam
A Okamoto, H Matsuoka, M Saito, Y Takayama, M Takamura, OPTICAL REVIEW, 6, 3, 189, 195, May 1999
We propose a new optical network device photorefractive connection module (PRCM) which operates as optical switch, amplifier and signal distributor controlled by parallel optical signals. Simple optical control bus systems can be realized by cascade connection of PRCMs. PRCM branches off a desired channel from the spatial multiplexed optical bus line by appropriate setting of the control beam pattern. PRCM uses cross polarized four wave mixing (CPFWM) with extraordinary polarized writing beams and an ordinary polarized reading beam to achieve a high connection gain to the next PRCM stage. We analyze the phase matching angle of CPFWM in which the optical paths of two pump beams are slightly different. The phase conjugate reflectivity indicating a branching ratio of optical signal is derived and calculated in consideration of the phase mismatching Delta k. The optimum pump ratio and the grating vector orientation for the largest phase conjugate reflectivity and signal amplification factor are discussed for optical design of PRCM. Since the measured signal beam power after passing through the BaTiO(3) crystal is three or four times higher than its incident power, PRCM has a sufficient connection gain for optical bus and interconnection systems., OPTICAL SOC JAPAN, English

Analysis and experiment of beam-ranning novelty filter
吉田 匡, 岡本 淳, 高山 佳久, 佐藤 邦宏, Proceedings of the IEICE General Conference, 1999, 1, 352, 352, 08 Mar. 1999
The Institute of Electronics, Information and Communication Engineers, Japanese

Analysis of Threshold in Controlling of Optical Bistability
OKADA Hajime, OKAMOTO Atsushi, TAKAYAMA Yoshihisa, SATO Kunihiro, Technical report of IEICE. LQE, 98, 510, 31, 36, 20 Jan. 1999
We have reported that one of the bistable value of the phase conjugate reflectivity is selected by illuminating the erase beam in photorefractive four-wave mixing with beam fanning. In this paper, a bistable region of the phase conjugate reflectivity is clarified by solving the coupling wave equations for the first time. Then the phase conjugate reflectivity is calculated by the temporal response analysis in consideration of the intensity variation of the erase beam, and we prove the validity of the bistable region. Besides, we show that one of the bistable value of the phase conjugate reflectivity can be selected in experiments., The Institute of Electronics, Information and Communication Engineers, Japanese

Free-space all-optical interconnection with a photorefractive crystal
Tsutomu Nakada, Atsushi Okamoto, Yoshihisa Takayama, Kunihim SatO, CLEO/Pacific Rim 1999 - Pacific Rim Conference on Lasers and Electro-Optics, 2, 373, 374, 1999
Recently, optical interconnection devices with parallel processing have been studied. Especially, expectations of an all-optical interconnection have been rising, and using a cat conjugator in a photorefractive crystal has been proposed to realize an optically controlled interconnection. In this report we propose a free-space all-optical interconnection device using the beam-fanning effect in a photorefractive crystal and perform 4 × 4 operations experimentally., Institute of Electrical and Electronics Engineers Inc., English

Proposition of all-optical switch with photorefractive crystal and analysis of the influence of the phase mismatching
S. Honma, A. Okamoto, Y. Takayama, K. Sato, CLEO/Pacific Rim 1999 - Pacific Rim Conference on Lasers and Electro-Optics, 2, 573, 574, 01 Jan. 1999
© 1999 IEEE. We propose an all-optical switch controlled by the phase difference of the two control beams with photorefractive effect that induce strong nonlinear effect by relatively low beam power. We explain the concept of this switch, and calculate intensity of signal beam at each output port, then show that the switch can work. We also analyze the influence of phase mismatching in order to operate the switch efficiently.

Photorefractive connection module and multistage optical bus system
Atsushi Okamoto, Junichi Nomusa, Hisashi Matsuoka, Yoshihisa Takayama, Kunihiro Sato, CLEO/Pacific Rim 1999 - Pacific Rim Conference on Lasers and Electro-Optics, 2, 371, 372, 01 Jan. 1999
© 1999 IEEE. We show the advantages of using several photorefractive connection modules (PRCMs) and the properties of the branching gain and the bus gain of the multistage PRCM system. We also performed experiments with two-stage-connected PRCMs composed of BaTiO3 crystals.

Tsutomu Nakada, Atsushi Okamoto, Yoshihisa Takayama, Kunihiro Sato: “Free-space All-optical Interconnection with a Photorefractive Crystal”, CLEO/Pacific Rim99 TECHNICAL DIGEST, Volume 2, pp.373-374 (1999)*　　　　　　　　　　　　　　　
1999

Hajime Okada, Atsushi Okamoto, Yoshihisa Takayama, Kunihiro Sato: “Control Method of Bistable Values of Phase Conjugate Reflectivity by Erase Beam in Photorefractive Four-Wave Mixing with Beam Fanning”, Optical Society of America, Trends in Optics and ・・・　　　　　　　　　　　　　　　
1999
Hajime Okada, Atsushi Okamoto, Yoshihisa Takayama, Kunihiro Sato: “Control Method of Bistable Values of Phase Conjugate Reflectivity by Erase Beam in Photorefractive Four-Wave Mixing with Beam Fanning”, Optical Society of America, Trends in Optics and Photonics, TOPS Volume XXVII, pp.287-291(1999)

Bistability Control of Phase Conjugate Reflectivity by Erase Beam in Photorefractive Four - Wave Mixing
OKADA Hajime, OKAMOTO Atsushi, TAKAYAMA Yoshihisa, SATO Kunihiro, The Transactions of the Institute of Electronics,Information and Communication Engineers. C-(0xF9C1), J82-C-I, 8, 477, 483, 1999
ホトリフラクティブ結晶を用いた4波混合において, 結晶の非線形効果が強い場合には, 発生する位相共役光は多値をとる. 本論文では, 前進ポンプ光の代わりに結晶中で発生するファニング光を用いた4波混合において, プローブ光に対する位相共役光の比である位相共役反射率の双安定値を, 消去光によって制御する方法を新たに提案する. ファニング光を含む4波混合を解析的に解くのは非常に困難であるが, プローブ光の一部がファニングし, 相互作用領域で前進ポンプ光として作用するモデルを用いることによって, 従来の4波混合の解析手法を適用することができる. まず位相共役反射率の定常解析を行い, 消去光の強度に対して位相共役反射率が双安定値をもつことを示す. 次に時間応答解析により, 消去光の強度を変化させ, 位相共役反射率の双安定値を制御する. 最後に実験によって, 理論との比較検討を行う., The Institute of Electronics, Information and Communication Engineers, Japanese

Atsushi Okamoto, Junichi Nomura, Hisashi Matsuoka, Yoshihisa Takayama, Kunihiro Sato: “Complementary Arrangement of Photorefractive Connection Module for Optical Bus System”, Optical Society of America, Trends in Optics and Photonics, TOPS Volume XXVII・・・　　　　　　　　　　　　　　　
1999
Atsushi Okamoto, Junichi Nomura, Hisashi Matsuoka, Yoshihisa Takayama, Kunihiro Sato: “Complementary Arrangement of Photorefractive Connection Module for Optical Bus System”, Optical Society of America, Trends in Optics and Photonics, TOPS Volume XXVII, pp.568-574(1999)

Atsushi Okamoto, Yoshihisa Takayama, Hajime Okada: “ OPTICAL CONTROLLED VECTOR MULTIPLIER WITH PHOTOREFRACTIVE FOUR-WAVE MIXING”, Micro optics Conference-99, MF32, pp.236-239(1999)*　　　　　　　　　　　　　　　
1999

Masatoshi Bunsen, Atsushi Okamoto, Motoyuki Ogawa, Kazunori Ikeda: “CROSS TALK REDUCTION AND NON-DESTRUCTIVE TECHNIQUE WITH PHOTOREFRACTIVE HOLOGRAPHIC MEMORY”, Micro optics Conference-99, MF34, pp.244-247(1999)*　　　　　　　　　　　　　　　
1999

A. Okamoto, K. Watanabe, H. Matsuoka, Y. Takayama：”PRCM and its optical bus application by photorefractive four-wave mixing with cross-polarization pumping”, Proceedings of SPIE(Optical Engineering for Sensing and Nanotechnology - ICOSN'99), 3740, pp.4・・・　　　　　　　　　　　　　　　
1999
A. Okamoto, K. Watanabe, H. Matsuoka, Y. Takayama：”PRCM and its optical bus application by photorefractive four-wave mixing with cross-polarization pumping”, Proceedings of SPIE(Optical Engineering for Sensing and Nanotechnology - ICOSN'99), 3740, pp.450-453 (1999)*

Atsushi Okamoto, Junichi Nomura, Hisashi Matsuoka, Yoshihisa Takayama, Kunihiro Sato: “Photorefractive Connection Module and Multistage Optical Bus System”, CLEO/Pacific Rim99 TECHNICAL DIGEST, Volume 2, pp.371-372 (1999)*　　　　　　　　　　　　　　　
1999

Satoshi Honma, Atsushi Okamoto, and Yoshihisa Takayama: “All-optical Photorefractive Switch with Phase Difference between Control Beams”, Optical Society of America, Trends in Optics and Photonics, TOPS Volume XXVII, pp.575-580(1999)　　　　　　　　　　　　　　　
1999

Atsushi Okamoto, Tsutomu Nakada, Satoshi Honma : ”Reconfigurable Optical Interconnection Controlled by Light, with Photorefractive Technique”, PROCEEDINGS APCC/OECC’99, Vol.1, 136, pp.397-400 (1999)*　　　　　　　　　　　　　　　
1999

Kentaro Watanabe, Atsushi Okamoto, Yoshihisa Takayama : “Gain Stabilization in Optical Bus System with Cascaded PRCM”, PROCEEDINGS APCC/OECC’99, Vol.1, 136, pp.409-412 (1999)*　　　　　　　　　　　　　　　
1999

Satoshi Honma, Atushi Okamoto, Yoshihisa Takayama, Kunihiro Sato: “Proposition of All-optical Switch with Photorefractive Crystal and Analysis of the Influence of the Phase Mismatching”, CLEO/Pacific Rim99 TECHNICAL DIGEST, Volume 2, pp.573-574 (1999)*　　　　　　　　　　　　　　　
1999

Operative conditions of beam-fanning novelty filter in photorefractive crystals
YOSHIDA Tadashi, OKAMOTO Atsushi, TAKAYAMA Yoshihisa, SATO Kunihiro, Technical report of IEICE. OPE, 98, 472, 25, 30, 15 Dec. 1998
We reveal the angle range of c-axis to operate beam-fanning novelty filter in an available photorefractive crystals, which is one of the devices to detect what is new in a input image. First, we explain the phenomenon of beam-fanning and the mechanism of beam-fanning novelty filter. Then, we show the method for analyzing beam-fanning with fourier transforms. We reveal the conditions suitable for the novelty detection of c-axis angular regions in beam-fanning novelty filter by numerical analysis. Besides we verify numerical results experimentally., The Institute of Electronics, Information and Communication Engineers, Japanese

Optical deflect switch with the photorefractive effect
HONMA Satoshi, OKAMOTO Atushi, TAKAYAMA Yoshihisa, Technical report of IEICE. PS, 98, 362, 31, 36, 23 Oct. 1998
We propose a deflect switch with photorefractive effect which can be control optically.First, we present a optical setup of the optical deflect switch. Next, we explain the basic theory of the switch with spatial distribution of the photorefractive grating which depend on the phase difference of control beams. And we derive the coupled wave education of them. Calcuating the intensity variation of signal and control beams, we analyze the deflect switching property., The Institute of Electronics, Information and Communication Engineers, Japanese

The analysis of cross talk in disk-type memory with cross polarized reflection grating
OGAWA Motoyuki, OKAMOTO Atsushi, SATO Kunihiro, TAKAYAMA Yoshihisa, Technical report of IEICE. LQE, 98, 342, 35, 40, 21 Oct. 1998
In this paper, we apply the phase mismatching property of the cross polarized reflection grating in order to show the condition for suppressing the cross talk in the disk-type memory. First, we show that the reflection grating is suitable for realizing the disk-type memory with photorefractive four-wave mixing. Next, we analyze the influence of the signal beam angle and the pump ratio, difined by intensity ratio of reading beam to reference beam, on the phase mismatching property. And we consider the dependency of the cross talk on the phase mismatching. Also we analyze the influence of spherical reference beam on the cross talk. Furthermore, we show the experiment of the phase mismatching property of the cross polarized reflection grating and compare with the theoretical analysis., The Institute of Electronics, Information and Communication Engineers, Japanese

The analysis of refreshing systems in optical neural networks with photorefractive crystals
OKU Yusuke, OKAMOTO Atsushi, TAKAYAMA Yoshihisa, Technical report of IEICE. LQE, 98, 342, 41, 46, 21 Oct. 1998
We report theoretical and expermental analysis of refreshing systems which are necessary for optical neural networks with photorefractive crystals. In the theoretical analysis, first, we show that refreshing systems are effective for sustaining holograms. And we reveal the properties of output beam intensity of the system for a pair of Cat mirrors reflectivities. These Cat Mirrors have an effect on sustenance and amplification of holograms. Then, we consider the optimum conditions to realize refreshing systems. Next, we examine the properties of beam intensity of output from the refreshing system for writing and reading beams intensities. In the end, we prove our theoretical analysis by experiments., The Institute of Electronics, Information and Communication Engineers, Japanese

Multi-solutions control of photorefractive four-wave mixing
TAKAYAMA Yoshihisa, OKAMOTO Atsushi, SATO Kunihiro, Technical report of IEICE. LQE, 98, 255, 13, 18, 27 Aug. 1998
We show a method to converge the phase conjugate reflectivity of the four-wave mixing to one of its multi-solutions for the first time. The phase conjugate reflectivity calculated by steady-state analysis has at most three solutions with a certain coupling strength. Then, we analyze the temporal behavior of the four-wave mixing with consideration of the phase difference of interaction beams, and show that two values of the reflectivity among the three can be selected by controlling the initial condition of the phase difference. In addition, we represent the state transition diagrams of the four-wave mixing and suggest a possibility of an all-optical switch or all-optical memory by the photorefractive four-wave mixing., The Institute of Electronics, Information and Communication Engineers, Japanese

Squeezed-state parameter with respect to phase in the intercavity squeezer
Nihei Hiroyuki, Okamoto Atsushi, Sato Kunihiro, Proceedings of the IEICE General Conference, 1998, 1, 375, 375, 06 Mar. 1998
The Institute of Electronics, Information and Communication Engineers, Japanese

Photorefractive disk-type memory with cross polarized reflection grating
Ogawa Motoyuki, Okamoto Astsushi, Sato Kunihiro, Takayama Yoshihisa, Proceedings of the IEICE General Conference, 1998, 1, 384, 384, 06 Mar. 1998
The Institute of Electronics, Information and Communication Engineers, Japanese

Optical flip-flop with two photorefractive four-wave mixing
Takayama Yoshihisa, Okamoto Atsushi, Sato Kunihiro, Proceedings of the IEICE General Conference, 1998, 1, 06 Mar. 1998
The Institute of Electronics, Information and Communication Engineers, Japanese

Gain stabilization in optical bus system with cascaded PRCM
K. Watanabe, A. Okamoto, Y. Takayama, 5th Asia-Pacific Conference Communications and 4th Optoloelectronics Communications Conference: The Conference-Vitality to New Century, APCC/OECC 1999, 1, 136, 409, 412, 01 Jan. 1998
© 1999 China Inst. Of Communications. We show the method for suppression of the variation of the busline intensity in an optical bus system with cascaded PRCM (PhotoRefractive Connection Module) in spite of turning on or off of the reading beam in each PRCM stage. In this analysis, we use the BaTiO3crystal, to take advantage of the large coupling coefficients, as the photorefractive medium, and accordingly, the response time of this crystal is slow, of the order of several seconds.

2. Takayama, Y., Okamoto, A.,Saito, M. and Sato,K.: "Cross polarized photorefractive four-wave mixing with extraordinary writing beams and an ordinary reading beam", Appl. Opt., 37, 5: 2967-2973 (1998)＊　　　　　　　　　　　　　　　
1998

1. Takayama,Y.,Okamoto, A.,Sato, Kumagai,K. and Aizawa,Y.: "Study on optimum incident angles of cross polarized four-wave mixing with a photorefractive crystal", Opt. Rev., 5, 1: 49-54 (1998)＊　　　　　　　　　　　　　　　
1998

3. Matsuoka, H.,Okamoto, A., Sato, K., Takamura,M.: "Reflectivity of cross-polarized four-wave mixing in consideration of pump depletion", J. Opt. Soc. Am. B, 15, 5: 1545-1552 (1998)＊　　　　　　　　　　　　　　　
1998

4. Takamura, M., Okamoto A. and Sato,K.: "Steady-state analysis of photorefractive ring resonator with self-pumped four-wave mixing (PRRR-SPFWM)", IEICE, Trans. Electron., E81-C, 7: 1122-1127 (1998)＊　　　　　　　　　　　　　　　
1998

5. Okada, H., Okamoto, A., Takayama，Y.: "Bistability control of phase conjugate reflectivity by erase beam in photorefractive four wave mixing", Third Optoelectronics and Communications Conference (OECC'98) Technical Digest, 14P-33:252-253, Makuhari Me・・・　　　　　　　　　　　　　　　
1998
5. Okada, H., Okamoto, A., Takayama，Y.: "Bistability control of phase conjugate reflectivity by erase beam in photorefractive four wave mixing", Third Optoelectronics and Communications Conference (OECC'98) Technical Digest, 14P-33:252-253, Makuhari Messe (1998)＊

「Cat型位相共役器による消去光を用いた光インタコネクション」　　　　　　　　　　　　　　　
『電子情報通信学会論文誌』 C-I, J81-C-I, 9, 535, 543, 1998

Phase matching property of cross polarization four wave mixing in BaTiO3 crystal
M Saito, A Okamoto, K Sato, Y Takayama, OPTICAL REVIEW, 4, 6, 686, 690, Nov. 1997
Four wave mixing (FWM) is of considerable interest in generation of a phase conjugate beam with photorefractive crystals. The common methods of FWM are parallel polarization FWM and cross polarization FWM. In this paper, we analyze the phase matching property of the latter. First, we consider the phase matching condition, and derive equations representing the angler relationship of interacting beams. Then, we consider the phase mismatching which is caused by shift of the probe beam angle from the phase matching condition, and calculate the effect of the shift of this angle on the amount of phase mismatching. We also determine and closely examine the coupling constant., OPTICAL SOC JAPAN, English

Multi-stability and temporal response of phase conjugate reflectivity in SPFWM
OKU Yusuke, OKAMOTO Atsushi, TAKAYAMA Yoshihisa, Technical report of IEICE. OPE, 97, 312, 65, 70, 14 Oct. 1997
We analyze multi-stability and temporal response of phase conjugate reflectivity in SPFWM(Self-Pumped Four-Wave Mixing) theoretically. The analysis is effective in a refreshing system which is necessary for an optical neural network with photorefractive crystals. In the steady-state analysis, we show multi-stability of phase conjugate reflectivity in SPFWM, such as in parallel-polarized four wave mixing. In the analysis of temporal response, we reveal the properties of the phase conjugate reflectivity for the coupling strength, the probe ratio, the reflectivity of a Cat mirror. Then, we consider the appropriate conditions to realize a refreshing system., The Institute of Electronics, Information and Communication Engineers, Japanese

Consideration of optimum incident beam angles of cross polarized four-wave mixing
TAKAYAMA Yoshihisa, OKAMOTO Atsushi, SATO Kunihiro, KUMAGAI Kazuhumi, AIZAWA Yugo, Technical report of IEICE. OPE, 97, 312, 59, 64, 14 Oct. 1997
We consider the optimum incident beam angles of the cross polarized four-wave. First, the phase matching angles are obtained in the both operation modes with ordinary writing beams and an extraordinary reading beam which we call Mode1 and with extraordinary writing beams and an ordinary reading beam which we call Mode2, respectively. Next, practicable angle ranges of the incident beams are shown with consideration of the total reflection of the phase conjugate beam in the both cases that the writing beams are on the same boundary of the crystal and that the writing beams are on the neighboring boundaries, respectively. As the result, the coupling coefficient within the angle range is obtained and the optimum incident beam angles of the cross polarized four-wave mixing to realize the effective beam interaction in Mode1 and Mode2 are obtained, respectively., The Institute of Electronics, Information and Communication Engineers, Japanese

Steady state analysis and experiment of the cross-polarized two-wave mixing under phase matching condition in BaTiO_3 crystals
YOSHIDA Naohiro, OKAMOTO Atsushi, SATO Kunihiro, TAKAYAMA Yosihisa, INOUE Tadahiko, Technical report of IEICE. OPE, 97, 312, 71, 76, 14 Oct. 1997
In this paper, we analyze the codirectional and contradirectional cross polarized two-wave mixing (CPTWM) in BaTiO_3 crystals, and examine experimentally. First, the phase matching condition which gives maximum conversion efficiency in cross polarized forward four-wave mixing (CPFFWM) is studied. CPFFWM is under the specific condition, regarded as CPTWM with polarization switching property as well as amplification property. Then, the closed form solution for codirectional and contradirectional CPTWM is derived, and polarization switching property is revealed. Besides, the polarization switching property is confirmed experimentally., The Institute of Electronics, Information and Communication Engineers, Japanese

High transient reflectivity of four-wave mixing in a BaTiO3 crystal by a pulsed pump beam
Y Takayama, A Okamoto, K Sato, JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS, 14, 10, 2570, 2576, Oct. 1997
We propose a method to obtain higher phase-conjugate reflectivity by using a pulsed pump beam as the reading beam. A qualitative explanation of our method is given. Then we calculate the transient phase-conjugate reflectivity, considering that the reading beam erases the grating in a photorefractive crystal. The reflectivity when a continuous reading beam is used is compared with that when the pulsed beam is used. We prove experimentally that approximately three times greater reflectivity can be obtained with a pulsed reading beam. (C) 1997 Optical Society of America., OPTICAL SOC AMER, English

Phase matching of reflection grating in cross polarized four-wave mixing
Saito Motoki, Okamoto Atsushi, Takayama Yoshihisa, Proceedings of the IEICE General Conference, 1997, 1, 446, 446, 06 Mar. 1997
ホトリフラクティブ結晶を用いた4波混合の研究が盛んに行われ, 交差偏光結合を用いた解析もされている。しかし, その多くは透過形回折格子の解析のみであった。そこで本報告では, 交差偏光結合を用いた透過形及び反射形回折格子について解析し, その上比較を行う。, The Institute of Electronics, Information and Communication Engineers, Japanese

Bistability control of photorefractive four-wave mixing by forward pump beam
Takayama Yoshihisa, Okamoto Atsushi, Sato Kunihiro, Proceedings of the IEICE General Conference, 1997, 1, 444, 444, 06 Mar. 1997
Introduction Four-wave mixing with a photorefractive crystal have been studied actively and their bistable properties have been reported. But no idea to control the bistability have been obtained. So, we propose a method to control the bistability and demonstrate it theoretically and experimentally iri this report., The Institute of Electronics, Information and Communication Engineers, English

Optical Interconnection with four-wave mixing using an erase beam
Aizawa Yugo, Okamoto Atsushi, Sato Kunihiro, Proceedings of the IEICE General Conference, 1997, 1, 451, 451, 06 Mar. 1997
光インターコネクションとは, 従来の計算機では電気的に行われている配線を光で行うものである。これにより超並列計算機の配線ボトルネックの解消が期待できる。本報告では, 入射光と偏波が直交している消去光を用いた画像処理操作を応用して, 4波混合と消去光を用いた新たな光インターコネクションデバイスを提案して, その実験を行う。, The Institute of Electronics, Information and Communication Engineers, Japanese

Analysis and experiment of temporal response in cross polarization four-wave mixing with BaTiO_3 crystal
IKEDA Kazunori, OKAMOTO Atsushi, TAKAYAMA Yoshihisa, AIZAWA Yugo, Technical report of IEICE. LQE, 97, 35, 79, 84, 14 Feb. 1997
We analyze the temporal response of the cross polarization four-wave mixing in BaTiO_3 photorefractive crystal. The coupling equations which describe the interaction among forward pump beam, backward pump beam, phase conjugate beam and probe beam are derived. We explain the correlation between coupling coefficients of ordinary wave and those of extraordinary waves. The generation process of the phase conjugate beam is shown and we analyze that the phase conjugate reflectivity in consideration on the variation of the pump ratio and the probe ratio. In addition, the experiment with a BaTiO_3 crystal is performed., The Institute of Electronics, Information and Communication Engineers, Japanese

Temporal analysis of photorefractive two-wave mixing with phase difference and its application of novelty filter
TAKAYAMA Yoshihisa, OKAMOTO Atsushi, Technical report of IEICE. LQE, 97, 35, 73, 78, 14 Feb. 1997
Temporal property of photorefractive two-wave mixing with phase difference is analyzed for the first time. First, equations which describe the variations of the optical intensity and phase difference between two beams interacting each other are derived. It is shown that the phase difference varies both temporally and spatially even if the coupling coefficient is real number. Next, the temporal properties of the intensity and the phase difference in the photorefractive interaction region are analyzed in the case that the initial phase difference is changed. In addition, one of the setups for the novelty filter by the two-wave mixing is shown. In the case of continuously moving image, the time resolution of the novelty filter is investigated., The Institute of Electronics, Information and Communication Engineers, Japanese

Calculation and experiment on diffraction efficiency of pulse beam operating four-wave mixing in photorefractive crystal
Koji Enbutsu, Atsushi Okamoto, Yoshihisa Takayama, Kunihiro Sato, Electronics and Communications in Japan, Part II: Electronics (English translation of Denshi Tsushin Gakkai Ronbunshi), 80, 10, 18, 01 Jan. 1997
Four-wave mixing using the photorefractive crystal is one of the methods used to generate the phase-conjugate optical beam. This paper considers the case where the pulse beam is used for the backward pump and calculates the diffraction efficiency. The coupled wave equation that describes the four-wave mixing process using the photorefractive crystal is analyzed numerically by Euler's method, and the transient characteristics of the diffraction efficiency are calculated. The following situation is considered. A crystal reaches the steady state, being radiated by two beams, i.e., the forward pump beam and the probe beam, and only the transmission diffraction grating is produced. Then, the continuous beam or the pulse beam is incident to the crystal as the backward pump. The transient characteristics of the diffraction efficiency are compared and it is shown that the diffraction efficiency is greatly improved by using the pulse beam. In order to verify the results of this study, a BaTiO3 crystal is used as the photorefractive crystal, and the phase conjugate beam generation experiment is tried. The measured waveform for the case where the continuous beam and the pulse beam are incident as the backward pump is shown and improvement of the diffraction efficiency is demonstrated by pulsed beam. © 1998 Scripta Technica.

Bistable phase-conjugate reflectivity controlled by a forward pump beam
Yoshihisa Takayama, Atsushi Okamoto, Mototsugu Takamura, Kunihiro Sato, Journal of the Optical Society of America B: Optical Physics, 14, 2664, 2669, 01 Jan. 1997
One of the typical methods to generate the phase-conjugate beam is four-wave mixing with a photorefractive crystal. It is known that the phase-conjugate reflectivity shows the bistability in some cases. Analyzing the temporal property of four-wave mixing, we offer a new method to control the bistable phase-conjugate reflectivity, and we perform an experiment of the bistability control by the method. An equation to obtain the threshold value of the coupling strength for showing the bistability is derived by a steady-state analysis of four-wave mixing, and the temporal property of four-wave mixing is studied with two different initial conditions that are used for letting the phase-conjugate reflectivity R converge to an off state (R = 0) or to an on state (R > 0). The initial condition for the converging off state is that the forward pump beam is turned off throughout. The condition for the converging on state is that the forward pump beam is turned on in advance, and after enough time passes, it is turned off. In both conditions, the backward pump beam and the probe beam continue to illuminate throughout. Whereas both optical arrangements are equivalent after setting up these initial conditions, each phase-conjugate reflectivity converges to different stationary values, R = 0 and R > 0. Besides, an experiment is performed and we actually control the bistability by this method. Furthermore, the temporal and the spatial variation of the refractive-index grating in the photorefractive crystal is investigated, and the process of the bistability is explained. © 1997 Optical Society of America.

Takayama, Y., Okamoto, A., Sato, K. and Takamura, M. : "Bistable phase conjugate reflectivity controlled by forward pump beam", J. Opt. Soc. Am. B., 14(10) : 2664-2669 (1997)＊　　　　　　　　　　　　　　　
1997

Takamura, M., Okamoto, A., Sato, K. and Takayama, Y. : "Unidirectional／Bidirectional Switchable Ring Resonator with Photorefractive Self-Pumped Four-Wave Mixing", Proc. 1997 Topical Meeting on Photorefractive Materials, Effects and Devices (Optical Soc・・・　　　　　　　　　　　　　　　
1997
Takamura, M., Okamoto, A., Sato, K. and Takayama, Y. : "Unidirectional／Bidirectional Switchable Ring Resonator with Photorefractive Self-Pumped Four-Wave Mixing", Proc. 1997 Topical Meeting on Photorefractive Materials, Effects and Devices (Optical Society of America, PR'97), FP 25 : 621-624 (1997)＊

Saito, M., Okamoto, A., Takayama, Y. and Takamura, M. : "Phase matching property of cross polarized four wave mixing in BaTiO3 crystal and optical bus application", Proc. 1997 Topical Meeting on Photorefractive Materials, Effects and Devices (Optical S・・・　　　　　　　　　　　　　　　
1997
Saito, M., Okamoto, A., Takayama, Y. and Takamura, M. : "Phase matching property of cross polarized four wave mixing in BaTiO3 crystal and optical bus application", Proc. 1997 Topical Meeting on Photorefractive Materials, Effects and Devices (Optical Society of America. PR'97), WP 28 : 204-207 (1997)＊

Takayama, Y., Okamoto, A., Sato, K and Saito, M. ＊ : "Method to control the bistability of four-wavemixing with a photorefractive crystal", Proc. 1997 Topical Meeting on Photorefractive Materials, Effects and Devices (Optical Society of America, PR‘97)・・・　　　　　　　　　　　　　　　
1997
Takayama, Y., Okamoto, A., Sato, K and Saito, M. ＊ : "Method to control the bistability of four-wavemixing with a photorefractive crystal", Proc. 1997 Topical Meeting on Photorefractive Materials, Effects and Devices (Optical Society of America, PR‘97), WP26 : 196-197 (1997)＊

「ホトリフラクティブ結晶とパルス光を用いた４光波混合における回折効率の計算と実験」　　　　　　　　　　　　　　　
『電子情報通信学会論文誌』, C-I, J80-C-1(1)/,18-24, 1997

「ホトリフラクティブ結晶を用いた４波混合における双安定性の前進ポンプ光による制御」　　　　　　　　　　　　　　　
『電子情報通信学会論文誌』, c-I, J80-c-I(11)/,510-516, 1997

Cross polarized photorefractive coupling with extraordinary writing beams and an ordinary reading beam and application to optical switch
TAKAYAMA Yoshihisa, OKAMOTO Atsushi, SAITO Motoki, SATO Kunihiro, Technical report of IEICE. OPE, 96, 410, 43, 48, 12 Dec. 1996
Cross polarized photorefractlve coupling with extraordinary writing beams and an ordinary reading beam is analyzed In this paper, first, the coupling coefficient is calculated both cases that the ordinary beams interact and that the extraordinary beams interact respectively. Second, the phase match angle and the phase mismatching is calculated. As the result, sharp angular filtering property of the this four-wave mixing is obtained. Besides the experimental result which measured the phase conjugate beam power by cross polarized coupling is shown. At last, an optical switch is proposed as an application of the cross polarized photorefractive coupling, The Institute of Electronics, Information and Communication Engineers, Japanese

Spatial phase dependence of the Squeezed parameter with respect to phase
NIHEI Hiroyuki, OKAMOTO Atsushi, SATO Kunihiro, Technical report of IEICE. LQE, 96, 399, 91, 96, 10 Dec. 1996
An altemative approach to derive the phase diagram which shows generation process of the squeezed variance is reported. Using this phase diagram, a spatial phase dependence of the squeezed parameter with respect to phase is shown. Furthermore, considering the spatial phase dependence of the squeezed parameter, the transmission characteristic of squeezed quantum noise generated via interactive squeezer is calculated., The Institute of Electronics, Information and Communication Engineers, Japanese

Optical interconnection with a cat conjugator and erase beam
AIZAWA Yuugo, OKAMOTO Atsushi, SATO Kunihiro, IEICE technical report. EMD, 96, 217, 67, 72, 21 Aug. 1996
We can perform the real-time image-processing operations by applying an external crase beam to a self-pumped phase conjugator. Incident beam including the image data creates the index grating inside the photorefractive crystal BaTiO_3. The erase beam has the effect of destroying the index grating, so it can modify the image data. Applying this theory, we suggest a new method to construct the optical interconnection. First, the decreasing of the phase conjugate reflectivity by applying the erase beam is theoretically analyzed. Next, the method of achieving the optical interconnection is shown by optical vector multiplication and erase beam. Finally, the optical interconnection experiments of 2×2 and 4×4 are performed with a BaTiO_3 photorefractive crystal and a Ar laser., The Institute of Electronics, Information and Communication Engineers, Japanese

Bistable condition of phase conjugate reflectivity by four-wave mixing with photorefractive crystal
TAKAYAMA Yoshihisa, OKAMOTO Atsushi, SATO Kunihiro, IEICE technical report. EMD, 96, 217, 61, 66, 21 Aug. 1996
The bistable condition of the phase conjugate reflectivity by the four-wave mixing with a photorefractive crystal is analyzed for the first time. It has been known that the phase conjugate reflectivity has bistable property, that is, two or more values of reflectivity exist for a given set of incident beam power and coupling strength. We show that the convergence value of the phase conjugate reflectivity can be controlled by the initial condition of the backward pump beam, by temporal analysis of the four-wave mixing., The Institute of Electronics, Information and Communication Engineers, Japanese

Reflectivity of Photorefractive Four Wave Mixing with Cross Polarized Pumping Beams in Consideration of Phase Mis-Matching
OKAMOTO Atsushi, SATO Kunihiro, TAKAMURA Mototsugu, SAITO Motoki, TAKAYAMA Yoshihisa, IEICE technical report. EMD, 96, 217, 79, 84, 21 Aug. 1996
To examine the characteristics of photorefractive four-wave mixing that uses cross polarized pump beams, strict solutions for coupling mode equations in undepleted pump approximation are obtained. The acceptance angle when BaTiO_3 crystals are used is first found by calculating the phase conjugate reflectivity of cross polarization coupling systems. Furthermore, an experiment is conducted using BaTiO_3 crystals and phase conjugate beam is generated successfully using cross polarization coupling. In a new trial in the experiment, a high reflectivity is obtained by shifting the angle of the diffraction grating vector on the c-axis of crystals from 90 degrees. Also, a new concept of PRCM is proposed for applications in optical communication systems such as optical interconnection and optical bus systems., The Institute of Electronics, Information and Communication Engineers, Japanese

Properties of oscillation intensities in photorefractive ring resonator with self-pumped four-wave mixing
TAKAMURA Mototsugu, OKAMOTO Atsushi, SATO Kunihiro, Technical report of IEICE. LQE, 96, 98, 85, 90, 18 Jun. 1996
We first suggested a photorefractive ring resonator with self-pumped four-wave mixing in which the backward pump beam is complex conjugate of the forward pump beam, and analyzed the properties of oscillation intensities in it. Giving the boundary conditions of a ring resonator and pump beams, we derived the oscillation intensities by solving the coupling equations of four-wave mixing in photorefractive crystal. Then, we calculated the oscillation intensities as functions of coupling strength for various values of reflectivity of mirrors constituting the cavity and of Cat mirror. We considered such phenomena in detail that the threshold coupling strength or oscillation depends on reflectivity of Cat mirror and that oscillation occurs bidirectionally or unidirectionally due to magnitude of coupling strength., The Institute of Electronics, Information and Communication Engineers, Japanese

Effect of Pump Beam Angle on Diffraction Image of Phase Conjugate Mirror with Gaussian Beam Pumping
Yamada Masahide, Okamoto Atsushi, Sato Kunihiro, Proceedings of the IEICE General Conference, 1996, 1, 354, 354, 11 Mar. 1996
位相共役波を画像処理に応用する際には、位相共役鏡による回折像の特性解析が検討課題となる。本報告では、より実際的な特性解析を行う目的から、ポンプ光にガウスビームを用い、ポンプ光の入射角の変化を考慮した位相共役鏡の回折像について解析レポンプ光の入射角の影響を数値計算によって検討する。, The Institute of Electronics, Information and Communication Engineers, Japanese

High-efficiency transient phase conjugation by turning on reading beam incident upon steady-state transmission grating in BaTiO3 crystal
Y Takayama, A Okamoto, K Sato, OPTICS COMMUNICATIONS, 123, 4-6, 603, 606, Feb. 1996
Transient high diffraction efficiency of phase-conjugate output in a photorefractive crystal of BaTiO3 was measured for the case in which the reading beam illuminates the transmission grating, which has been formed by the two writing beams and in steady-state before the illumination. The experimental results show that the peak value of the diffraction efficiency can be over ten times as large as its stationary value., ELSEVIER SCIENCE BV, English

Analysis of oscillation intensities in photorefractive ring resonator with self-pumped four-wave mixing
Takamura Mototsugu, Okamoto Atsushi, Sato Kunihiro, Proceedings of the IEICE General Conference, 351, 351, 1996
ホトリフラクティブ結晶内での4波混合を用いたリング共振器における双方向発振の解析は既に報告されている。定常発振状態にある場合、発振光強度は4波混合の結合強度によって変化する。本報告では、光学系の簡略化などの目的から自己励起形4波混合を用いたリング共振器を新たに提案し、結合強度に対する発振光強度の特性を理論解析する。, The Institute of Electronics, Information and Communication Engineers, Japanese

「自己励起形４波混合における位相共役反射率の特性」　　　　　　　　　　　　　　　
『電子情報通信学会論文誌C-I』, J79-C-I, 4, 109, 116, 1996

Angular Dependence of Phase Conjugate Intensity in Forward Four-wave Mixing with Gaussian Beam Pumping
HAGIWARA Kei, OKAMOTO Atsushi, KANEKO Hiroyuki, KOYANAGI Kojiro, SATO Kunihiro, The Transactions of the Institute of Electronics,Information and Communication Engineers. C-(0xF9C1), J79-C-I, 8, 295, 302, 1996
位相共役光学の進展に伴い, 前進4波混合に関する研究が盛んに行われている. 実用的な光学系設計の観点から, 有限なスポットサイズのポンピング光を用いた場合における位相共役光強度の光線角度依存性を検討することは, 特に光波の分離を考える上で重要である. 本論文では, 光力ー媒質を用いた前進4波混合において, 位相共役光の光線角度に対する強度分布を初めて理論解析した. まず, 位相共役光強度が比較的小さく, 二つのポンピング光の重なり合った領域に比べ薄い非線形媒質を用いたときの位相共役光強度を導出した. また, その結果を用いて位相共役光のz軸に対する出射角,および,x-y面内における方位角に着目した数値計算を行った. 次に, 二つのポンピング光で形成される相互作用領域が媒質中にすべて含まれる十分に厚い媒質を用いた場合についても同様の解析を行った. 更に, 薄い媒質を用いた場合と厚い媒質の場合との相異を述べ, 平面波ポンピングの場合との比較, 検討も行った. 最後に, 厚い媒質についてガウスビームポンピングにおけるスポットサイズや波面曲率の変化が強度分布に及ぼす影響などについて述べた., The Institute of Electronics, Information and Communication Engineers, Japanese

Angular dependence on conversion efficiency on forward four-wave mixing in consideration of pump depletions
HAGIWARA Kei, OKAMOTO Atsushi, SATO Kunihiro, Technical report of IEICE. LQE, 95, 350, 87, 92, 13 Nov. 1995
In this report, we analyzed the phase-conjugate conversion efficiency of forward four-wave mixing with boxcar optical configration in consideration of pump depletions. First, phase-conjugate conversion efficiency is derived assuming that all beam intensities are variable. Second, we calculated the relation between conversion efficiency and coupling strength, varying the pump beam angle and pump ratio, and showed the possibility of multivalued conversion efficiency when phase matching is violated. At last, we analyzed the effect on angular mismatch between probe beam and pump ones., The Institute of Electronics, Information and Communication Engineers, Japanese

Analysis of the phase conjugate waves in variances
Nihei H, Okamoto A, Sato K, Mishima T, Abstracts of the meeting of the Physical Society of Japan. Annual meeting, 50, 2, 447, 447, 16 Mar. 1995
The Physical Society of Japan (JPS), Japanese

Analysis of and experiment on time response of four‐wave mixing in a photorefractive crystal
Yoshihisa Takayama, Atsushi Okamoto, Kunihiro Sato, Teruhito Mishima, Ichiro Sakuraba, Electronics and Communications in Japan (Part II: Electronics), 78, 4, 9, 19, 1995
Time variations of four‐wave mixing in photore‐fractive crystals is analyzed, and its relation to the physical parameters of the crystal is clarified. Experiments on phase‐conjugate light generation in a BaTiO3 crystal are performed, and the measured data are compared against the results of numerical calculations. Time variations of the coupling coefficient of the photorefractive effect and its relation to the physical parameters of the crystal are derived first and then the phase‐conjugate reflectivity of the transmission‐type diffraction grating is investigated. The pump ratio (the fraction of the forward to the backward pump intensities) and its effects on the time response of the phase‐conjugate reflectivity is for the first time clarified by numerical calculations. Experiments on phase‐conjugate light generation by four‐wave mixing in BaTiO3 are then done and the steady‐state power of the phase‐conjugate light together with the time response to steady state are measured. Finally, the effects of the pump ratio on the phase conjugate power and its time response are compared against experimental data. As a result, it is shown that when the pump ratio is increased nine times, the steady‐state power of the phase‐conjugate light increases approximately 30 times, theoretically, while the measured data indicates an increase that is 24 times. On the other hand, the time response is shown to be delayed four times, theoretically, while the measured value shows a delay of four and a half times. From these results, it is concluded that the time response of the BaTiO3 crystal can be controlled by adjustment of the pump ratio. Copyright © 1995 Wiley Periodicals, Inc., A Wiley Company, English

Analysis and Experiment on Temporal Respose of Four-Wave Mixing in Photorefractive Crystal
TAKAYAMA Yoshihisa, OKAMOTO Atsushi, SATO Kunihiro, MISHIMA Teruhito, SAKURABA Ichiro, The Transactions of the Institute of Electronics,Information and Communication Engineers. C-(0xF9C1), 77, 9, 481, 489, 25 Sep. 1994
ホトリフラクティブ結晶を用いた4波混合の時間応答特性を結晶の物性パラメータを考慮して新たに解析する.BaTiO_3結晶を用いて位相共役光発生の実験を行い,数値計算結果と測定結果を比較する.まず,ホトリフラクティブ効果における結合係数の時間的変化を,結晶の物性パラメータを用いて導き,透過形回折格子による位相共役反射率の時間応答を導出する.前進ポンプ光と後進ポンプ光の入射強度比であるポンプ比が位相共役反射率の時間応答に与える影響を数値計算によって初めて明らかにする.次に,BaTiO_3結晶を用いた4波混合による位相共役光発生の実験を行い,位相共役光電力の定常値と,定常値に達するまでの応答時間を測定する.最後に,ポンプ比の変化が位相共役光の定常値および応答時間に与える影響を解析結果と実験結果を用いて比較検討する.ポンプ比を9倍に大きくした場合,位相共役光電力の定常値は,理論計算値で約30倍,測定値で約24倍に増加した.一方,応答時間は,理論計算値で約4倍,測定値で約4.5倍遅くなった.これらの結果より,BaTiO_3結晶の応答時間をポンプ比によって制御できることを示している., The Institute of Electronics, Information and Communication Engineers, Japanese

28p-E-2 Analisys of the squeezed states with considering the initial phase of fields
Nihei Hiroyuki, Okamoto Atsushi, Mishima Teruhito, Abstracts of the meeting of the Physical Society of Japan. Annual meeting, 49, 2, 359, 359, 16 Mar. 1994
The Physical Society of Japan (JPS), Japanese

Properties of Reflectivities in Self-Pumped Phase Conjugators by Photorefractive Crystal
高山 佳久, 岡本 淳, 三島 瑛人, Bulletin of the Faculty of Engineering,Hokkaido University, 168, p21, 31, Feb. 1994
北海道大学 = Hokkaido University, Japanese

Reflectivity of Self-Pumped Phase Conjugator with Reflection Grating
TAKAYAMA Yoshihisa, OKAMOTO Atsushi, MISHIMA Teruhito, The Transactions of the Institute of Electronics,Information and Communication Engineers. C-(0xF9C1), 77, 1, 30, 32, 25 Jan. 1994
自己励起形位相共役器において,ホトリフラクティブ結晶中に反射形回折格子が生じている場合の位相共役反射率を新たに導出した.結晶の外部にある共振器を構成する鏡の反射率と位相共役反射率の関係を数値計算によって明らかにし,反射形回折格子の特性を検討した., The Institute of Electronics, Information and Communication Engineers, Japanese

Temporal response of four-wave mixing in photorefractive crystal
Takayama Yoshihisa, Okamoto Astushi, Sato Kunihiro, Mishima Teruhito, Sakuraba Ichiro, IEICE technical report. Electron devices, 93, 168, 15, 20, 26 Jul. 1993
We analyzed the temporal response of phase conjugate reflectivities in photorefractive crystal by four wave-mixing. First,assuming only transmission grating is generated,we offered the phase conjugate reflectivity that includes temporal parameters of photorefractive crystal.Where absorption in the crystal is neglected and the undepleted pumps approximatoin is made.Second, keeping probe beam power constant,we calculated the response time and steady-state value of the reflectivity by changing the ratio between forward-pump beam power and backward-pump beam power.In addition,we made a experiment and found the experimental result coincides with theoretical one qualitatively., The Institute of Electronics, Information and Communication Engineers, Japanese

ホログラム最新技術～感光材料の開発から実製品への応用まで～　　　　　　　　　　　　　　　
情報機構, 2007

ホログラフィックメモリーのシステムと材料　　　　　　　　　　　　　　　
シーエムシー出版, 2006

Systems, Devices and Materials for the Holographic Data Storage　　　　　　　　　　　　　　　
2006

Progressive Hologram Recording and Reconstruction Using Complex Amplitude Generation and Detection Technologies
Atsushi Okamoto, Atsushi Shibukawa, Akihisa Tomita, Masanori Takabayashi
International Symposium on Optical Memory 2013, Aug. 2013, Japanese, Invited oral presentation
[Invited], [International presentation]

Spatial mode excitation and separation using spatial phase control technology
A. Okamoto, A. Tomita, K. Kawabata, Y. Wakayama
CLEO-PR & OECC/PS 2013, Jul. 2013, English, Invited oral presentation
[Invited], [International presentation]

Recording and Reconstruction of 38-Level Spatial Quadrature-Amplitude Modulation Signal in Double-Referential Holographic Memory
ZUKERAN Keisuke, OKAMOTO Atsushi, TAKABAYASHI Masanori, SHIBUKAWA Atsushi, TOMITA Akihisa
ITE Technical Report, 15 Feb. 2013, Japanese, Invited oral presentation
We propose a double-referential holographic memory (DRHM) that can detect phase modulation signal by just entering reference beam into recording medium without additional system for generation and irradiation of the beam to interfere with signal beam. In this technique, by highly-accurate and simplified complex amplitude detection, high multi-level phase modulation signal and spatial quadrature-amplitude modulation (SQAM) signal become available, so it is expected that storage capacity and data transfer rate are greatly increased. In this paper, we describe the basic operation of the DRHM and evaluate multiple recording/reconstruction characteristics by numerical simulation. Besides, the method for furthermore improving reconstruction quality is newly proposed and its effectiveness is demonstrated., [Invited], [Domestic Conference]

岡本 淳, “光複素振幅の制御技術とモードの励振・分離に関する研究　　　　　　　　　　　　　　　
岡本 淳
フォトニックICT研究会, Aug. 2012, Japanese, Invited oral presentation
[Invited], [Domestic Conference]

空間位相制御技術を用いたモードの励振・分離に関する研究　　　　　　　　　　　　　　　
岡本 淳
OCS研究会, 第3回ディジタル信号処理による新しい光伝送技術～100G and Beyond～, Jul. 2012, Japanese, Invited oral presentation
[Invited], [Domestic Conference]

位相変調技術を用いた自己参照型ホログラフィックメモリ　　　　　　　　　　　　　　　
岡本 淳
フォトニクスポリマー研究会, Jun. 2012, Japanese, Invited oral presentation
[Invited], [Domestic Conference]

モード分割通信用の空間モード励振・分離技術　　　　　　　　　　　　　　　
岡本 淳
第59回応用物理学関係連合講演会, Mar. 2012, Japanese, Invited oral presentation
[Invited], [Domestic Conference]

Holographic Memory System with Spatial Quadrature Amplitude Modulation　　　　　　　　　　　　　　　
OKAMOTO Atsushi
Optics and Photonics Japan 2011, Nov. 2011, Japanese, Invited oral presentation
[Invited], [Domestic Conference]

BCI-1-7 Spatial mode excitation and separation for mode division multiplexing technology
Okamoto Atsushi, Soma Daiki, Oda Takuya, Tomita Akihisa, Wakayama Yuta
Proceedings of the Society Conference of IEICE, 30 Aug. 2011, Japanese
[Invited]

B-10-98 Ultra-broad tuning range of reconfigurable optical add-drop multiplexer using dynamic holographic diffraction grating
Wakayama Yuta, Okamoto Atsushi, Tomita Akihisa
Proceedings of the IEICE General Conference, 28 Feb. 2011, Japanese

Dynamic Hologram for Mode-Division Multiplexing Communication Technology　　　　　　　　　　　　　　　
OKAMOTO Atsushi
31th Annual Meeting of The Laser Society of Japan, Jan. 2011, Japanese, Invited oral presentation
[Invited], [Domestic Conference]

B-10-52 Experiment on All-optical Demultiplexer for Mode Division Multiplex Communication Technique
Oda Takuya, Okamoto Atsushi, Morita Kazuyuki
Proceedings of the IEICE General Conference, 02 Mar. 2010, Japanese

BI-8-2 High Performance Intersatellite Communication based on Double Phase Conjugation Technology
Okamoto Atsushi, Fujita Tomohiro, Wakayama Yuta, Takayama Yoshihisa
Proceedings of the IEICE General Conference, 02 Mar. 2010, Japanese

Autonomic Waveguide Formation with Sn2P2S6 Crystal and Multi-layered Reconfigurable Optical Wiring
KOJIMA YASUNORI, OKAMOTO ATSUSHI, GRABAR ALEXANDER A, SATO KUNIHIRO, TAKABAYASHI MASANORI
電気・情報関係学会北海道支部連合大会講演論文集(CD-ROM), 17 Oct. 2009, English

光複素振幅制御技術を用いたモード拡散多重光ファイバ通信に関する研究　　　　　　　　　　　　　　　
科学研究費補助金
2013
岡本 淳
Principal investigator, Competitive research funding

光ファイバMIMO通信技術創出に向けての多重空間モード分離・結合デバイスの研究　　　　　　　　　　　　　　　
2009 - 2011
岡本 淳
科学研究費補助金, Principal investigator, Competitive research funding

光集積回路・導波路チップ間のリコンフュギュラブルな自動配線技術　　　　　　　　　　　　　　　
平成20年度SCAT研究助成(研究費助成)
2008 - 2010
岡本 淳
テレコム先端技術研究支援センター, Principal investigator, Competitive research funding

ダイナミック・リコンフィギュラブルな光素子の創出　　　　　　　　　　　　　　　
[e11] 第39回三菱財団研究助成 自然科学研究助成
2008 - 2009
岡本 淳
三菱財団, Principal investigator, Competitive research funding

しきい値秘密分散機能を有する全光学的な暗号・認証技術に関する研究　　　　　　　　　　　　　　　
科学研究費補助金
2008 - 2009
岡本 淳
Principal investigator, Competitive research funding

ホログラム記録・消去装置およびホログラム記録・消去方法　　　　　　　　　　　　　　　
Patent right, 文仙正俊, 古田洋介, 岡本 淳
特願2008-016095
特許4997428

光波長フィルタ装置　　　　　　　　　　　　　　　
Patent right
特許公開２００９－１４５４２９

ホログラム複製装置およびホログラム複製方法　　　　　　　　　　　　　　　
Patent right
特許公開２００８－２８７１０７

記録再生装置、記録再生方法、再生装置及び再生方法　　　　　　　　　　　　　　　
Patent right
特開2008-97738

記録再生装置、記録再生方法、再生装置及び再生方法　　　　　　　　　　　　　　　
Patent right
特許公開２００８－９７７３８

多重ホログラム転写装置および多重ホログラム転写方法　　　　　　　　　　　　　　　
Patent right, 伊藤輝将, 岡本 淳
特願2006-143051
特開2007-316152
特許4815595

ファニング光結合構造およびそのファニング光結合構造を用いた光増幅器　　　　　　　　　　　　　　　
Patent right
特開2007-43087

双方向光配線形成方法　　　　　　　　　　　　　　　
Patent right
特開2007-41519

画像記録方法　　　　　　　　　　　　　　　
Patent right, 岡本 淳, 森竹 潔
特願2006-052904
特開2007-232919
特許4876222

ホログラムメモリ装置およびこの装置に適用されるホログラムリフレッシュ方法　　　　　　　　　　　　　　　
Patent right, 岡本 淳, 伊藤 輝将
特願2005-169796
特開2006-343586
特許4765067

光中継装置および光中継方法　　　　　　　　　　　　　　　
Patent right, 岡本 淳, 村中 秀史
特願2005-133199
特許4670047

光インターコネクション装置および光インターコネクション方法　　　　　　　　　　　　　　　
Patent right, 岡本 淳, 本藤 聡一郎, 高木 清史
特願2004-346725
特開2005-189844

位相共役光発生装置　　　　　　　　　　　　　　　
Patent right
特開2005-292792

ホログラム処理装置およびホログラム処理方法　　　　　　　　　　　　　　　
Patent right
特開2006-208858

ホログラム記録装置およびホログラム記録方法　　　　　　　　　　　　　　　
Patent right
特開2006-184570

光インターコネクション装置および光インターコネクション方法　　　　　　　　　　　　　　　
Patent right, 岡本 淳, 植村 俊介, 高木 清史
特願2005-039465
特開2005-309385
特許4533770

ホログラムメモリ装置およびホログラム記録方法　　　　　　　　　　　　　　　
Patent right
特開2005-189845

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