Optical information processing using photorefractive BSO.
Several optical information processing tasks are implemented using photorefractive BSO as a dynamic holographic medium. The physical basis for the mechanism which allows the implementation of these devices is studied. The properties of BSO which make it particularly attractive as a processing medium are highlighted, and experimental results are presented to demonstrate its practical limitations. An extensive study is presented of the influence of optical bias on the grating formation characteristics. This leads to a documentation of the optimum conditions for transient enhancement of a beam diffracted from such a grating. This transient enhancement can be controlled to provide ideal characteristics for the implementation of transient devices such as a novelty filter. A novelty filter utilising this transient enhancement is subsequently demonstrated. It exhibits good temporal discrimination through the choice of suitable external optical conditions, and the use of digital thresholding. The overall device operates at T.V. frame rates. Results are also presented of various optical correlators using BSO. These include the optical intensity correlator. The unique properties of the intensity correlator are stressed by practical demonstration. Specifically, the relative intolerance of the intensity correlator (compared with coherent correlators) to the position of the various components is demonstrated. Also, the spatially incoherent readout light allows the use of a low-opticalquality liquid crystal television (LCTV) as a low-cost spatial light modulator. Output results are then presented from the correlator using the LCTV as a dynamic readout device. This provides an updatable hologram as the reference of the correlator which is interrogated at frame rates by the LCTV. Finally, the temporal discrimination of the novelty filter is combined with the character recognition ability of the intensity correlator. This produces an optical processor which will recognise a particular object but will only register it at the output stage when it is moving.