High-speed optical image correlator

Claim 1

An optical image correlator, comprising: a) a source of a coherent input beam of light; b) a source of a coherent output beam of light; c) means for impressing on the input beam a spatial, intensity-modulation pattern corresponding to at least a first input image; d) a lens for creating a Fourier transform of the modulation pattern; and e) a photorefractive medium for recording the Fourier transform as an intensity modulation pattern, and for modulating the output beam according to the recorded pattern, CHARACTERIZED IN THAT f) the photorefractive medium comprises a semi-insulating, multiple quantum well structure that includes, in alternation, plural quantum well layers, and plural barrier layers of a higher bandgap than the quantum well layers; g) the quantum well structure is enclosed between two dielectric layers; h) the quantum well structure comprises: a first epitaxially grown portion adjacent one of the dielectric layers, and a second epitaxially grown portion adjacent the first portion and distal said dielectric layer; i) associated with the first portion is a first carrier lifetime and associated with the second portion is a second carrier lifetime; and j) the first portion is grown at a lower temperature than the second portion, such that the first carrier lifetime is smaller than the second carrier lifetime, and the first carrier lifetime is less than one picosecond.