Optical Considerations in the Design of Digital Optical Computers.

The promise of digital optical computing is based on massively parallel interconnections between logic gates, which allow for novel architectures, and the possibility of ultrafast switching devices. This paper spells out the computational requirements and limitations for nonlinear optical devices and optical interconnects. Relationships between the optical properties of devices (transmission, contrast) and their potential computational properties (fan-in, fan-out) are derived. The accuracy of intensity levels required in the system are estimated. The requirements for a minimal device useful for digital optical computing are stated. The "volume" of a device in phase-space limits fan-in, switching energy and the degree of space variance in the interconnections. Space invariant and space variant interconnections are compared. Limits of random interconnects by volume holograms are discussed.