A phenomenon exhibited by certain resonant optical structures whereby it is possible to have two stable steady transmission states for the device, depending upon the history of the input. Such a bistable device may be useful for optical computing elements because of its memory characteristics. The bistability can result from the intrinsic properties of the optical device or from some external feedback such as an electrical voltage supplied by another device. This second type, extrinsic or hybrid optical bistability, is not true optical bistability.