Nonvolatile holographic memories in photorefractive media

Summary form only given. Photorefractive crystals are a promising storage medium for holographic memories. The fact that data stored in photorefractive crystals can be erased and replaced with fresh data makes these materials well suited for read/write memories. The recorded holograms are erased by simply illuminating the crystal with a uniform light beam that redistributes uniformly the stored charge pattern. Unfortunately, the same thing also happens when the crystal is illuminated to read the data out. In this paper the various methods that have been developed for preventing decay during read-out will be reviewed and compared. Specifically, thermal fixing, electrical fixing, dual wavelength operation, 2-photon recording, and periodic copying will be considered.