Dynamic Optical Cross-Correlator Using A Liquid Crystal Light Valve And A Bismuth Silicon Oxide Crystal In The Fourier Plane

A complete real-time cross-correlator using both a photoconductive bismuth silicon oxide [Bi12Si020 (BSO)] liquid crystal light valve for data input and a photorefractive BSO crystal as a dynamic holographic filter is presented. Some specific properties of this dynamic optical processor are reported. The following optimum operating conditions of the light valve were used in the experiment: driving voltages, 30 Vrms; frequency, 300 Hz; and writing energy of the light valve in the blue-green spectral range, 150 /uJ cm -2. For a 15µm thick pentylcyanobiphenyl (PCB) liquid crystal layer, the measured spatial resolution at 50% MTF is 12 1p mm-1, thus ensuring a potential processing capability of 300X:300 pixels. The optimized time constant of the operating optical processor, including both the light valve and the photorefractive BSO crystal, is around 50 ms for 0.2 mW cm-2 incident intensity on the light valve at the green line of an argon laser. Experimental cross-correlation results for various types of digital or analog data written on the light valve are shown in this paper. Compensation of the residual distortions of the incident signal beam emerging from the light valve has been achieved by generation of a phase conjugate wavefront diffracted by a high efficiency holographic lens recorded on dichrornated gelatin.