| Photorefractive materials offer the possibility of optical signal processing at milliwatt power levels. The potential applications of photorefraction for optical if formation recording, dynamic optical memories, phase conjugation, edge enhancement, pattern recognition, and many others stimulated the research towards explanation of the detail mechanisms of this phenomenon. The introduction of photorefractive polymers over the last decade made a crucial conceptual change in material optimization.; We present the results of a balanced theoretical and experimental effort to rigorously investigate wave mixing, higher order generation, edge enhancement and edge-enhanced joint transform correlation in photorefractive polymers. To this end, we start from a theoretical model of two-beam interaction in photorefractive polymers, in which higher (non-Bragg) diffraction orders and beam fanning are also included. The effect of different geometrical parameters, such as bisector angle and interbeam angle, on power exchange between the interacting beams is first studied numerically. The effect of beam fanning and applied voltage on beam coupling is also investigated. Results are compared with heuristic predictions and existing experimental results. The effect of incident beam ratios on beam coupling in two-beam coupling geometry is predicted.; We also demonstrate a simple all-optical realization of programmable edge-enhanced correlation using novel photorefractive polymers. Edge-enhanced correlation provides sharper correlation peaks, leading to easier target identification in the presence of noise or clutter. Traditionally, edge-enhanced correlation is achieved by digitally preprocessing the input scenes. We show that higher order generation in a two-wave mixing scheme contains the edge enhancement of the object. Experimental results are reconciled with numerical simulations. Also, this arrangement provides a scheme of writing joint transform correlation holograms in the material, which can be read by a third incident beam. The observed correlation is edge-enhanced, and the correlation peak increases with the applied voltage across the material. Numerical results in the absence and presence of beam fanning are presented.; With minor modifications, the same configuration provides a scheme of writing joint transform correlation in the material which can be instantaneously read directly by one of the writing beams. |
