Introduction

Optical processors hold tremendous potential for processing many information channels in parallel, each at very high bandwidth, and in small volumes with low power consumption (VanderLugt, 1992). Major classes of operations that optics can perform include integral transformations such as Fourier transforms and correlations, and matrix operations, e.g. vector–matrix multiplication (Lee, 1987). Many, but not all, of these are made possible by the remarkable property that a ‘Fourier transform lens’ generates, at the back focal plane, the two-dimensional (2-D) Fourier transform of phase and amplitude information input at the front focal plane.

Initial feasibility demonstrations of optical signal processors are usually performed in the laboratory using existing components, but these often do not come close to fully exploiting the potential of the optical processor, and often disregard practical implementation issues such as: how much phase distortion is permissible in a critical lens, or what will be the effect of vibration or temperature changes in the field, and is it feasible to have a given dynamic range and information capacity in the same processor? Therefore the aim of most subsequent optical hardware development is to answer these questions and overcome any deficiencies.

Much effort has gone into the development of the critical active optical devices, such as infrared laser diodes, spatial light modulators (SLMs) and photodetector arrays, and new device concepts and improvements on existing devices continue to occur (Lee & VanderLugt, 1989).