Experimental systems implementation of a hybrid optical-digital correlator.

A high-speed hybrid optical-digital correlator system was designed, constructed, modeled, and demonstrated experimentally. This correlator is capable of operation at approximately 3000 correlations/s. The input scene is digitized at a resolution of 512 x 512 pixels and the phase information of the two-dimensional fast Fourier transform calculated and displayed in the correlator filter plane at normal video frame rates. High-fidelity reference template images are stored in a phase-conjugating optical memory placed at the nominal input plane of the correlator and reconstructed with a high-speed acousto-optic scanner; this allows for cross correlation of the entire reference data set with the input scene within one frame period. A high-speed CCD camera is used to capture the correlation-plane image, and rapid correlation-plane processing is achieved with a parallel processing architecture.

Pixelated liquid-crystal light valve for neural network application.

The liquid-crystal light valve (LCLV) is a useful component for performing integration, thresholding, and gain functions in optical neural networks. Integration of the neural activation channels is implemented by pixelation of the LCLV, with use of a structured metallic layer between the photoconductor and the liquid-crystal layer. Measurements are presented for this type of valve, examples of which were prepared for two specific neural network implementations. The valve fabrication and measurement were carried out at the State Optical Institute, St. Petersburg, Russia, and the modeling and system applications were investigated at the Institute of Microtechnology, Neuchâtel, Switzerland.

Pure phase correlator with photorefractive filter memory.

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.