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An updatable optical correlator which uses a photorefractive compound semiconductor to generate real-time matched filters is proposed. Using compound semiconductors offers high speed with low optical input intensities. Here we discuss issues affecting the performance of this correlator. This includes an analysis of the Bragg diffraction and a discussion of the speed and power considerations of these materials. Experimental results obtained using photorefractive GaAs are also presented.

Three image processing experiments were performed by degenerate four-wave mixing in photorefractive GaAs. The experiments were imaging by phase conjugation, edge enhancement, and autocorrelation. The results show that undoped, semi-insulating, liquid-encapsulated Czochralski-grown GaAs crystals can be used as effective optical processing media despite their small electro-optic coefficient.

The maximum mean square projection (MMSP) filter is proposed for distortion invariant recognition. It classifies images according to the energy projected onto an N-dimensional subspace. The MMSP filter is implemented in an updatable optical correlator where correlations from multiple filters are time integrated on the output detector array.