Abstract

A new design for obtaining optical bistability in two dimensions is reported in this paper. This design uses optical feedback on a photoconductor-twisted nematic liquid crystal (PC-TNLC) device with a new structure. The PC-TNLC device is essentially a 2-D array of optically controlled light values. The device structure with a new arrangement of the photoconductor, the liquid crystal film, and a patterned transparent electrode gives better control over its input–output (I–O) response, which is important in obtaining bistable operation. A theoretical analysis is carried out to determine the conditions under which bistability occurs. A sharp transition from the off to on state in the I–O response suggests that the thresholding operation on gray scale input images can be performed. Experimentally, an 8 × 8 PC-TNLC device with optical feedback was demonstrated to have bistable behavior. The on:off ratio of 50:1 was obtained in the output. This device was also used to perform thresholding operation on a gray scale image with eight levels. The observed value of γ for the thresholding operation was 8. Such a bistable device was shown to have potential applications in digital optical processing.

© 1981 Optical Society of America

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