Abstract

Optical joint transform correlation exploits the interference of two side-by-side coherently illuminated objects. One object is a reference; the other could be a real-time input to the correlator. Optical Fourier transformation of the object plane for two similar objects produces a fringed interference pattern, with the fringe spacing inversely proportional to the object spacing. Nonlinear coherent-to-coherent conversion by a spatial light modulator in the Fourier plane, followed by inverse Fourier transformation, yields paired correlation spots symmetric about the optical axis. Unlike classical correlators, no complex (phase and magnitude) filters are required, only coherent input and reference objects. The spatial light modulators suitable for the nonlinear conversion, such as magnetooptic and liquid crystal devices, map amplitude objects into phase objects. The effects of this mapping on the correlation were investigated by recording joint transform filters on a phase-only holographic recording medium with nonlinear exposure characteristics. The resulting correlations were observed; SNR and overall optical efficiency were found to compare favorably with the output of classical VanderLugt correlators.

© 1987 Optical Society of America