ABSTRACT

A function has no time spread (memory). Optical functions are functions of a two-dimensional input distribution, typically a two-dimensional output distribution and mostly linear and space invariant. The most general function would be a mapping of an m-dimensional quantity onto an n-dimensional quantity which is nonlinear and space variant. If the lateral dimension is quantized and the amplitude is binary, one can speak of a boolean function. It can be implemented by a circuit with different input channels and output channels. Finite state machines ideally require a combinatorial logic function and a feedback loop containing latches. This chapter lists some approaches to optical finite state machines as a basis for optical digital computers. The feedback loop contains space variant interconnections and the gates provide combinatorial logic function between a pair of two inputs. The combinatorial logic is realized with the method of shadow casting logic.