Abstract

Numerous digital optical computing architectures have been proposed and demonstrated in the past years^{1 2 3 4}. However, there is still considerable debate as to the value of these architectures in general-purpose digital computing. The main issue is that the switching speed of the devices employed is slower than electronic transistors. The continuously improving speed and cost of electronic circuits can lead to the misleading view that the future of optics is exclusively in the interconnection domain. We show here that in many practical applications, optoelectronic circuits can perform logic operations faster than electronics⁵. Previous comparisons of electronic logic gates with their optoelectronic counterparts did not consider the effect of gate fanin and fanout on in-circuit performance. Yet electronic gates suffer considerable performance degradation with increasing fanin and fanout. This paper will address how to systematically exploit the inherent high fanin and fanout abilities of optoelectronics to reduce circuit delay. We hope our work will provide a new design paradigm for computer architects. In addition, since fanin and fanout behavior have important implications for device designers, we hope it will provide guidance to device developers by identifying the most desirable characteristics of optoelectronic logic elements from the circuit designer’s point of view.

© 1995 Optical Society of America