Abstract

An optical tracking novelty filter that performs the process of optical image differentiation using an interferometric arrangement involving BaTiO₃ has recently been demonstrated [1]. This device exploits differential optical phase changes and is therefore restricted to highlighting or tracking phase objects only. Other schemes for coherent optical image differentiation based on two beam coupling in BaTiO₃ have also been demonstrated [2, 3]. These two devices rely on destructive interference between reference and signal beams under static conditions but require high optical quality for the BaTiO₃ crystal so that the transmitted images do not suffer from any spatial distortion. In this paper we report a novel arrangement for optical differentiation of images in time that uses an optical processor based on the spatial frequency dependent response time of photorefractive Bi₁₂SiO₂₀ in a phase conjugate Michelson interferometric configuration. The device is capable of differentiating both amplitude and phase objects. To our knowledge this is the first time that BSO with its inherent fast response time, some two or three orders of magnitude faster than BaTiO₃, has been used for such optical differentiation in time.

© 1990 Optical Society of America