Optical logic redux

Twenty years ago IBM physicist Robert Keyes published a paper entitled “Optical Logic—in the light of computer technology.” It caused an instant furor in the fledgling optical logic community. Now, 20 years after that devastating critique, the field of optical logic has grown enormously. There are literally thousands of papers. Many of them are collected in a bibliography given here. Was Keyes’ critique wrong? Have opticists simply ignored what Keyes pointed out? Have new developments made some of his remarks not quite so relevant? We argue here that •Keyes was and still is mostly correct, but that may change in a few years•Many researchers have indeed simply ignored what he said•New developments in both optical logic and its applications open niches for optical logic that Keyes did not (and probably could not) anticipate•New and anticipated developments in electronics may increase the role for optics