Parallel associative search by use of a volume holographic memory

Volume holographic memory can offer massively parallel associative search capability in addition to high capacity data storage. After holograms have been stored into a photosensitive material, an optical correlation of an input user query against all co-locationally stored patterns can be made simultaneously, resulting in fast search speed. We describe a correlator based on a 90 degree geometry holographic data storage system using thick (~l cm) storage media. Two important parameters considered are the correlation error rate and minimum size of the search template. A minimum template area less than 0.05% relative to the whole image area has been demonstrated. Due to the strict Bragg selectivity of volume holograms in thick media, the correlator has very small shift invariance. Thus it lends itself best to the search of relational databases, where information can have a fixed position on the stored record. We describe a demonstration database application designed to make best use of the volume holographic correlator