Pure phase correlator with photorefractive filter memory

Abstract

We report on the investigation of a new compact configuration of an inverted VanderLugt-type correlator system. The phase of the Fourier transform of the image to be recognized is displayed on a phase-modulating electrically addressed spatial light modulator. This phase display is compared with the phase of the Fourier transforms of a reference library recorded in a photorefractive LiNbO 3 crystal. Angular hologram multiplexing permits fast data access, and the use of the conjugated replica of the stored templates leads to an elimination of phase distortions introduced by the optical system. With such a configuration, the correlator is fully shift invariant in spite of the photorefractive crystal thickness and has good discrimination with sharp correlation peaks.

<title>Phase-shifting joint transform correlator with a wavelength-shifted laser diode</title>

“…6 A chirp-encoded method in the JTC has been shown to separate between the correlation signals of the target and the reference objects and the self-correlation signals of the target objects along optical axis. 7 Pure phase correlation method [8][9][10][11] has been performed to improve the sharpness of correlation peak, the light efficiency, and the discrimination capability. The JTC layout can be relaxed the requirement of large space-bandwidth product to make a pure phase correlator by a digital holographic technique.…”

Experimental systems implementation of a hybrid optical–digital correlator

“…Other aspects of device performance, such as phase distortion due to SLM nonflatness, nonlinear phase response, residual amplitude coupling, and so on, also have implications for the ultimate performance one can obtain from the system. We have, therefore, used the compact phase-conjugating correlator devised by Duelli et al 15 to overcome most of these problems in conjunction with the hybrid concept to produce a high-speed correlator system.…”

Compact phase-conjugating correlator: simulation and experimental analysis

“…Imperfections of SLM's, such as phase distortion owing to nonflatness, nonlinear phase response, residual amplitude coupling, and so on, also have implications for ultimate performance. The compact phase-conjugating correlator ͑PCC͒ devised by Duelli et al 2 has been adopted to obviate some of these problems, while retaining the hybrid, high-speed concept.…”