The evolution of optical computing from simple arithmetic computing to complex logical computing closely parallels the transition of optical computing from the analog to the digital domain. The significance of optical crossbars in both arithmetic and logic-based optical computing systems is considered. An emphasis is placed on the unique ability of digital optical systems to implement extremely complex combinational logic structures. The significance of fan-in and fan-out is examined. The emergence of a new class of optoelectronic programmable logic arrays (PLA's) is discussed. A comparison of the potential operational limits of these devices to those of their electronic counterparts is presented.
"Historical Perspectives: Optical Crossbars And Optical Computing", Proc. SPIE 0752, Digital Optical Computing, (11 August 1987); doi: 10.1117/12.939903; https://doi.org/10.1117/12.939903