|
|
|
“Nonlinear Real-Time Optical Signal Processing”
by A.A. Sawchuk, T.C. Strand, A.R. Tanguay, Jr. A. Armand, D. Drake, and J. Michaelson
June 15, 1978
The results of a one-year research program in nonlinear real-time optical signal processing are described. Fast parallel nonlinear operations on signals with large time-bandwidth and space-bandwidth products are a need for many current and future information processing systems. Several approaches to the problem have been investigated. The first achieves nonlinearities by parallel filtering of a pulse-width modulated continuous level input. The pulse-width modulation is done by halftoning and hard-clipping with real-time optical input transducers. A real-time logarithm function has been achieved by this method, and a novel feedback processor explored to improve the necessary hard-clipping operation. Many results predicting degradations of non-ideal real-time devices and precompensation for these effects have been obtained. Another approach is to use the inherent nonlinear characteristics of real-time devices to directly achieve selected nonlinear functions without halftone processing. A parallel optical analog-to-digital converter based on this principle is described. A last approach is to exploit the variable grating mode of liquid crystal light valves for the conversion of local input levels to different spatial frequencies. A nonlinear function is achieved by selective attenuation and recombination of these systems are given. The project has been a joint effort between the University of Southern California Image Processing Institute (USCIPI) and the Hughes Research Laboratories (HRL), Malibu, California. The USC group has developed new systems and techniques for nonlinear optical processing and the HRL group has performed work on various real-time devices.