Abstract

A nonlinear joint transform image correlator is investigated. The Fourier transform interference intensity is thresholded to provide higher correlation peak intensity and a better defined correlation spot. Analytical expressions for the thresholded interference intensity are provided. The effects of nonlinearity at the Fourier plane on the correlation spots at the output plane are investigated. The correlation signals are determined in terms of the nonlinear characteristics of the spatial light modulator at the Fourier plane. We show that thresholding interference intensity results in a sum of infinite harmonic terms. Each harmonic is envelope modulated due to the nonlinear characteristics of the devices and phase modulated by m times the phase modulation of the nonthresholded interference intensity. The correct phase information about the correlation signal is recovered from the first-order harmonic of the thresholded interference intensity.

© 1988 Optical Society of America