Abstract

Recently, the combination of VLSI and liquid crystal technologies has resulted in a number of compact, high density spatial light modulators. In this paper, we present results on the design, fabrication, and demonstration of a novel, optically addressed VLSI/FLC de vice for insertion into a bipolar optoelectronic learning machine. The device consists of eight pixels, representing neurons. Each nueron consists of two photodetectors, a comparator, circuitry for target values, switching circuitry, and two output modulation pads. A thin layer of smectic C^* FLC (SCE-13) is sandwiched between the VLSI chip and a piece of glass coated with a transparent conductive oxide (TCO) acting as an electrode. To operate the device, a 2.5 V de bias is applied on the TCO electrode, and either 5 V or 0 V is provided on the modulation pads. The voltage on each pad is determined by the optical intensity and the target value. The device demonstrated an on / off contrast ratio of 5:1, a 10 90% rise time of 3 ms (limited by the low voltage placed across the FLC), and an input optical sensitivity of 2 nW/cm².

© 1992 Optical Society of America