PURE PHASE CORRELATOR WITH PHOTOREFRACTIVE FILTER MEMORY

We report on the investigation of a new compact configuration of an in verted VanderLugt-type correlator system. The phase of the Fourier tra nsform of the image to be recognized is displayed on a phase-modulatin g electrically addressed spatial light modulator. This phase display i s compared with the phase of the Fourier transforms of a reference lib rary recorded in a photorefractive LiNbO3 crystal. Angular hologram mu ltiplexing permits fast data access, and the use of the conjugated rep lica of the stored templates leads to an elimination of phase distorti ons introduced by the optical system. With such a configuration, the c orrelator is fully shift invariant in spite of the photorefractive cry stal thickness and has good discrimination with sharp correlation peak s. (C) 1997 Optical Society of America