Abstract

Conventional techniques for the design of distortion-invariant optical correlators presuppose the use of continuous amplitude and phase filters in the realized optical system. However, since programmable continuous amplitude and phase spatial light modulators (SLMs) do not exist, the capability of such correlators is severely limited. On the other hand, programmable SLMs limited to quantized levels of amplitude and/or phase are presently available. To make a versatile high-speed optical correlator a method of constructing a synthetic-discriminant-function matched spatial filter (SDF-MSF) that is tailored to utilize effectively these existing quantized SLMs is required. A technique in which the filter modulation is included in the synthesis of an SDF-MSF is presented. In the filter synthesis, a system of simultaneous nonlinear equations is solved with an iteration procedure. A computer simulation of the new method using threshold images of the Space Shuttle at a range of aspect angles was performed for phase-only and binary-phase-only filters. The filters constructed are capable of obtaining the specified peak-correlation response to within 1% with a high signal-to-clutter ratio for the one-class, two-class, and multilevel problems.

© 1987 Optical Society of America