Abstract

A few years ago, the predominant area of research in optical computing devices was to try to develop devices that could behave as optical logic gates or more specifically NOR gates. In theory, one could optically interconnect these NOR gates to implement arbitrary digital functions and ultimately a digital optical computer. Bistable devices based on non-linear optical materials in Fabry-Perot etalons were among those proposed, for these NOR gates [1,2] A variety of optoelectronic devices have also been investigated. One group of devices called self electro-optic effect devices (SEEDs) rely on changes in the optical absorption that can be induced by changes in an electric field perpendicular to the thin semiconductor layers in quantum well material [3,4]. If we place the quantum well material in the intrinsic region of a reverse biased diode, then as we apply a voltage across the diode we can change its absorption. We can also use the same device as a detector, generating photocurrent in response to an incident light beam. In a SF.FD, the photocurrent generated by one or more of these detectors causes the voltage to change across one or more modulators. Thus, a SEED has optical inputs for controlling optical outputs. One particularly useful device, the symmetric SEED (S-SEED) [5] consists of two of these quantum well p-i-n modulator/detector diodes connected electrically in series. It has the inherent characteristics of a set-reset latch, but can also do logic functions (such as NOR) by using a preset beam. It uses pairs of complementary optical signals, so it is insensitive to optical power supply fluctuations and operates with a wide dynamic range (1 nW - 500 μW). Uniform arrays of devices with as many as 32768 S-SEEDs have been made [6] and several system demonstrations have now been built using these devices [7].

© 1992 Optical Society of America