Abstract

Long term readout of the holographically stored information in photorefractive crystals remains an important issue for many optical processing and storage applications. In this paper, we report the experimental demonstration of a continuously readable holographic memory using two cascaded photorefractive crystals, for storage and amplification, respectively. The "storing crystal" is read out with a very weak intensity beam, while the "amplifying crystal" operates in a high-gain low-noise configuration. By this means, the writing-erasure cycle asymmetry is artificially improved, thus providing long term cw readout capabilities. Alternatively, this technique tolerates low diffraction efficiency in the memory crystal, thus increasing its capacity. To demonstrate this operating principle, we used combinations of LiNbO₃/BSO and BaTiO₃/BSO as storage/amplifier crystals. Continous redout of stored images for 23 h in LiNbO₃ and 40 min in BaTiO₃ were obtained.

© 1992 Optical Society of America