Programmable optical correlator

Claim 1

An optical correlation system comprising a source of coherent light, a photorefractive crystal capable of sustaining a degenerate four wave mixing process, a source of a reference image, and beam transmission means for directing first and second beams and an image beam through said crystal in an interaction region of said crystal to form an output beam through the degenerate four wave mixing process, characterized in that: said beam transmission means comprises means for modulating a first beam (10) from said source of coherent light with said reference image to form a reference beam and for directing said reference beam through said interaction region along a first axis and in a first polarization state; said beam transmission means further comprises means for directing an image beam (20) from said source of coherent light, having a source image modulation pattern impressed thereon, through said interaction region along an image axis at a grazing angle with respect to said first axis and in an image polarization state substantially orthogonal to said first polarization state, and; said beam transmission means further comprises means for directing a second beam (30) from said source of coherent light through said interaction region in a second polarization state substantially parallel to said first polarization state and along a second axis, whereby said first and second beams form a volume phase reflection hologram in said crystal, said image beam interacts with said volume phase reflection hologram, and the degenerate four wave mixing process generates said output beam having a correlation modulation pattern impressed thereon.