An optical image storage and processing device using electrooptic ZnS

Abstract

An image-sensing and memory device is described that photoconductively converts and electrostatically stores optical images at the interface between a UV sensitive ZnS film and an associated blocking electrode. Optical readout is accomplished by means of the Pockels electrooptic effect generated in the ZnS film by the electrostatic image. A high ratio of UV to visible photosensitivity (approximately 105:1 between 340 and 630 nm) allows pseudonondestructive readout of the stored image pattern. A device has been constructed and tested having an active sensing and storage area of 2 cm2with an observed limiting resolution of 85 line pairs/mm. A 340-nm exposure of 20 erg/cm2gives a 2:1 change in readout light intensity (100 erg/cm2gives a 10:1 change). Dark storage periods of approximately 100 h have been observed under room temperature conditions. The device can be erased electrically or optically and recycled. The device structure will be described along with the theory of operation in the sensing, storing, and readout modes. The lumped parameter equivalent circuit models and the equations that predict device performance will be discussed. This device is applicable as a reusable memory plane for use in coherent processors. It has been evaluated for this use by storing phase gratings and measuring their diffraction efficiency. Such operations as real-time correlation, Fourier transformation, and spatial filtering are made possible by this device.