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“Nonlinear Real-Time Optical Signal Processing Annual Technical Report”
by A.A. Sawchuk, T.C. Strand, A.R. Tanguay, Jr., A. Armand, J. Michaelson, M. Muha
April 14, 1979
The results of the second year of a two year research program in nonlinear real-time optical signal processing are described. The goal of the program is to extend fast parallel nonlinear operations to optical processing systems with large time-bandwidth and space-bandwidth products. Several approaches have been investigated. The most mature technique involves the parallel filtering of a pulse-width modulated continuous input obtained by halftoning and hard-clipping with real-time optical input devices. Real-time homomorphic and logarithmic filtering has been achieved by this method. A complete analysis of the system degradations due to non-ideal real-time devices has been made and several methods to compensate for these effects are described ad experimentally verified. A second technique uses the inherent nonlinear characteristics of a real-time device to achieve nonlinear functions in incoherent illumination without halftoning. An experimental three bit parallel optical analog-to-digital converter based on this principle is described. Another technique uses multiple liquid crystal light valves (LCLV's) to achieve electronically programmable time variable optical nonlinearities. A last technique uses the variable grating mode (VGM) of LCLV's to perform local frequency modulation as a function of the image brightness for nonlinear processing by selection and recombination of these frequencies. An experimental VGM LCLV and level slicing results are described. 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.