20 February 2007 Adaptive optics For holographic data storage
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Abstract
The characteristics of holographic recording in the presence of phase noise caused by air disturbances and by vibrations were studied. Diffraction efficiencies were calculated using the finite-difference time-domain method. The simulation results show that the amplitudes of fringes decreases with increasing phase noise, and thus diffraction efficiencies decrease. A novel method of phase compensation for holographic data storage is proposed. Interference fringes are incident on a charge coupled device (CCD) camera symmetrically positioned in relation to the recording media, and the fringes in the media are estimated using the fringes monitored by the camera. The phase information is calculated using a fast Fourier transform, and a phase modulator is set in the reference beam's path and driven to reduce the phase error, so that the phase at the CCD camera is stabilized. With this method, the standard deviation of the phase error is decreased to less than 1/10th that of the conventional method. The diffraction efficiencies of angle multiplex recording using photopolymer were measured. The diffraction efficiency with phase compensation at 0 degree was 700% larger than without it, and the total relative multiplexing number improved by 50%. When digital data are recorded, we found that the histogram distribution of the symbol "1" (a white signal) was a Gaussian density and the distribution of the symbol "0" (a black signal) was a Rayleigh density. We also proposed a novel SNR measure suitable for holographic data storage. When this phase compensation method was applied to digital holographic storage in which a spatial light modulator (SLM) was set on reference beam's path, a 5.0-dB improvement in SNR compared with the value without phase compensation was obtained. As holographic data storage can record phase, the proposed method can be made into a feasible technology.
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Norihiko Ishii, Norihiko Ishii, Tetsuhiko Muroi, Tetsuhiko Muroi, Nobuhiro Kinoshita, Nobuhiro Kinoshita, Koji Kamijo, Koji Kamijo, Naoki Shimidzu, Naoki Shimidzu, } "Adaptive optics For holographic data storage", Proc. SPIE 6488, Practical Holography XXI: Materials and Applications, 64880G (20 February 2007); doi: 10.1117/12.699731; https://doi.org/10.1117/12.699731
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