Abstract

Multiple volume holograms can be recorded in photorefractive crystals. Holograms are typically recorded by exposing the crystals to interference patterns of plane waves and signal beams. Any one of the two recording beams can be used to read the recorded holograms. Depending on the choice of the readout beam, a multiple-hologram memory can be configured either as an inner-product computer or as an imagery memory. We show experimental results of both configurations of our multiple-hologram memory. The storage capacity of a multiple-hologram memory is a function of the average diffraction efficiency/available readout energy, bandwidth of the optical system/ separation between holograms, and tolerable noise level. In an angle-multiplexed memory, utilizing fractal-space multiplexing can increase the storage bandwidth by over an order of magnitude. Angular separation between holograms and volume holographic cross-talk noise level are both minimal when the nominal included angle between plane waves and signal beams is 90°. The tradeoff of using a 90° geometry is a reduction in the average diffraction efficiency. We attempt to answer some of the questions involved in this tradeoff.

© 1992 Optical Society of America