Recent developments in digital optical computing

Abstract

Required elements in a digital optical computing (DOC) system are a nonlinearity (e.g., gates), interconnections, memory, and input/output (I/O). These may or may not be physically distinct units. The nonlinearity provides gain, regeneration of signal level, and noise reduction or elimination. I/O is required to interface with the outside world, electronic machines, or other optical machines. The nonlinearity and I/O dictate the most important limitations in DOC systems. New and improved devices are reducing the severity of these limitations. Memory may be built out of the nonlinearity and interconnections or may be separate. A hierarchy of memories may be employed; free-space propagation can function as memory; memory could be associative. The most important advantages of DOC systems are due to the interconnections and the resulting architectures that are made possible, e.g., massively interconnected processors that permit increased speed-up over their electronic counterparts. Digital optical computing systems can be characterized by the computations performed (numeric or symbolic), control structure (SIMD or MIMD, control flow, or data flow), likely instruction sets or software, speed of the logic, and by the type and location of the nonlinearity, interconnections, memory, and I/O. These issues are discussed in an overview of recent DOC systems.