Infrared wavelength multiplexed holographic storage in photorefractive LiNbO3

Abstract

Holographic optical storage in photorefractive LiNbO3 is important for parallel computing applications because of its large memory capacity. The practicality of memory systems will strongly rely on random access time and packagability. Advances in color tunable semiconductor lasers (SL's) may play an important role in holographic memory systems because SL's can be tuned in nanoseconds and packaged easily. However, they impose new requirements for holographic materials: sensitivity in the near infrared range and the ability to multiplex many images given a limited tuning range. To support such systems we have identified photorefractive specially doped LiNbO3 to provide high sensitivity in the SL range. The sensitivity of our crystals was evaluated experimentally for the range of 780 to 880 nm and compared with commercially available LiNbO3, demonstrating a sensitivity improvement of about an order of magnitude. The ability of volume holographic storage to wavelength-multiplex images was also investigated. Experimentally measured wavelength selectivity in a 1 mm thick LiNbO3 sample was 0.15 nm FWHM. We also investigated the BER of such memory systems by creating a noise model for holographic storage. Since the BER depends on the cross talk, it also depends on the wavelength separation of the stored images and strongly affects the number of images that can be stored. Experimentally measured BER will be compared with that of standard memory devices.