Optical signal processing using photorefractive crystals
I describe in this thesis various techniques of optical signal processing using photorefractive BSO and BaTiO3 crystals. Operations of contrast manipulation, motion detection and parallel optical logic operations are demonstrated. Dynamic instabilities have also been investigated in photorefractive BaTiO3, in the mutually pumped geometry. Contrast manipulation of optical images has been performed via degenerate four wave mixing in BSO and BaTiO3 crystals. In BSO the technique adopted has the apparent drawback of intensity reduction, due to low reflectivities achieved, while using BaTiO3, selective enhancement is achieved for specific Fourier components. An improved versatile technique of polarization encoding of the object Fourier transform has also been implemented with, and without the inclusion of photorefractive crystals. Applications of this technique for phase contrast imaging, and observation in the field of aerodynamics, and Fourier transform synthesis, has been proposed and demonstrated. Optical motion detection using the differential response time of multiplexed gratings in photorefractive BSO has been demonstrated. The operation of velocity filtering has also been demonstrated using complementary gratings in a BSO crystal, in which specific features are only detected at particular speeds. All sixteen basic parallel optical logic operations have been demonstrated using polarization encoding in a phase conjugate Michelson interferometer with a crystal of BSO as a phase conjugate mirror. Finally dynamic instabilities in BaTiO3 in the 'Bird-wing' mutually-pumped configuration have also been investigated, and a phenomenological model is developed. Additionally various improvements and refinements have been proposed which will make these techniques more flexible and versatile.