Companding nonlinearities in optical signal processing

Compression, expansion and rectification are well established noise reduction techniques in digital electronic communication systems. Photorefractive crystals provide high-resolution, real-time, low-power, parallel-nonlinear optical devices for performing these operations, and, in the last decade, considerable progress has been achieved in designing photorefractive devices with various functions and performance. We have recently proposed and demonstrated several photorefractive nonlinear techniques for reducing the following forms of noise: (1) additive random noise; (2) additive signal dependent noise; and (3) multiplicative zero mean complex noise. These noniinear approaches to noise reduction are not limited to photorefractives and may be implemented by alternative optical nonlinear technologies. In this paper, we present general optical nonlinear models for these noise reduction techniques and compare them with our photorefractive experiments