Speckle Generation by Phase-Only Spatial Modulators: Random Phase Properties ThatProduce Fully Complex Modulation and that Model Optical Processor Performance

摘要

Optoelectronic processors that use phase only and amplitude phase coupled spatiallight modulators (SLMs) can be profoundly affected by phase errors. These errors arise not only from irregularities in the modulators themselves, but at a number of points along the signal processing chain. Traditional theories of speckle generation by rough surface scattering are adapted to analyzing SLMs. SLMs are modeled as arrays of subapertures/pixels that are perturbed by random phase components (constant and linear retardations). The effects of not only random, but also systematic. phase errors on the performance of diffractive optical elements (DOEs) and optical correlators are evaluated. While traditional speckle theory models random surfaces as stationary random processes, SLMs can be programmed to produce nonstationary optical surfaces. This generalization is used to devise a new class of computer generated holographic algorithms, referred to as pseudorandom encoding. The method is notable in that it: (1) uses all available space bandwidth of the SLM; (2) produces diffraction patterns having large signal to noise ratio; and, most notably, (3) can be calculated in real time by serial processors. Simulations and experimental demonstrations using SLMs are presented, and applications to pattern recognition, optical interconnects, multispot beam steering, and acceleration of DOE design algorithms are described.