Photorefractive crystals for real-time image processing

Heavily iron doped lithium niobate photorefractive crystals are grown and characterized. The crystals have high diffraction efficiency and fast temporal response and hence are suitable for real-time image processing. Three applications of thin Fe: LiNb03 plates are demonstrated: the joint-transform correlator, the optical perception, and the hybrid image classifier. In the first and third systems, the heavily doped (0.5% mole) crystals are used. These crystals have fast temporal response (300-400 msec) and thus provide a means for real time optical processing. In the second system, a slightly light doped (0.1% mole) crystal is used. It has relatively long (> 1 minute) response time and is used for recording the dynamic memory in a neural network. Image recognition by these three systems are presented.