Motion detection, velocity filtering and the detection of change in a given scene are all important aspects for optical processing architectures and systems. So far several different techniques have been reported in the literature that use either all optical, or hybrid (optical plus electronic), schemes to implement novelty filter type operations. For essentially all-optical schemes the intrinsic advantages of parallel image subtraction arc clear. In this paper we report a different scheme for motion detection and velocity filtering which uses two spatially multiplexed gratings with a relative phase shift 130 degrees, (known as complementary gratings) in photorefractive BSO.
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