Contrast Manipulation and Controllable Spatial Filtering Via Photorefractive Four Wave Mixing and Two-Beam Coupling

Spatial filtering, which relies on the insertion of masks, slits or other objects such as stops in the Fourier transform plane of an optical imaging system, is a well established technique for optical image processing, These conventional methods, however, suffer from serious drawbacks such as the possibility of updating or renewing these Fourier masks at the speeds required for real-time processing.