Method for optically fixing holograms in photorefractive materials and a read/write memory based thereon

摘要

A method and read/write memory based thereon for storing phase holograms in a photorefractive crystalline material in which electric- field-mobile positive ions are associated with certain sites within the material broadly characterized by first forming a halogram (light interference pattern) in the material in order to redistribute the electrons therein to cause variations of the electric fields which variations represent the halogram, and then illuminating the material with light of a frequency in an absorption band of the ionic bond and having sufficient energy to cause the positive ions to be redistributed to neutralize the electric field variations caused by the electrons, whereat said positive ions remain fixed. As applied to a specific crystalline material, Fe:LiNbO.sub.3, having protons held in OH.sup.- bonds, a crystal of Fe:LiNbO.sub.3 is exposed to a light interference pattern to record the same as an electronic space charge pattern or hologram in the volume of the crystal by photo-excitation of electrons trapped at Fe+2 sites. Afterwards, or at the same time, the crystal is exposed to light at a proton absorption band in order to optically liberate the protons from OH.sup.- bonds within the Fe:LiNbO.sub.3 and, thereby, to neutralize the electronic pattern or halogram space charge and allow the protons to migrate and to create a proton space charge pattern which mirrors the electronic pattern or halogram and neutralizes the space charge patterns of the electrons. Thereafter, the protons remain fixed.