VELOCITY FILTERING USING COMPLEMENTARY GRATINGS IN PHOTOREFRACTIVE BSO

We demonstrate a new optical technique for velocity filtering and feature extraction of time varying optical images. The technique exploits the recording of complementary (multiplexed) gratings with a relative phase shift of 180-degrees in a photorefractive material, BSO, via a degenerate four wave mixing (DFWM) configuration. For experimental parameters, such as grating response time and optimised total input intensity, almost complete subtraction is achieved in the phase conjugate output. When motion occurs in the object plane a bright output image is observed depending on the experimental variables of feature size and velocity. We present results for motion detection of features of various dimensions at a range of speeds in both x and y directions and via Fourier plane observation.