Optical computing and the Fredkin gates.

The use of optics to implement the Boolean logic functions traditionally used in conventional electronic computing is an active area of optical computing research. Many proposed optical implementations duplicate the configuration of electronic logic gates and hence may not optimally utilize the full benefits of optical techniques. We present here a new optical gate, the Fredkin gate, which may, in principle, be minimally dissipative (i.e., exhibit reversible logic) and whose response time may be limited in some implementations only by the duration of optical pulses (i.e., in the picosecond range). Such gates, which consist of three input and three output lines, can be programmed to produce a standard set of Boolean functions and appear well matched to the parallelism of optics. We present here a number of optical implementations of Fredkin gates and suggest ways of composing their interconnections to achieve combinatorial logic, circulating memories and generalized interconnects.