Abstract
Adding to the success of optoelectronics in fiber-optic transmission and optical recording, there still remains a challenging peak of optical information processing. Introduction of optical technology in the field of information processing will be justified when the intrinsic properties of optical media such as very fast response (1) and parallelism (2) are fully exploited. A series of fundamental researches have been made along the line of all optical processing, where replacement of all the electronic devices with optical devices should help getting rid of RC time constant constraints. This approach, however, turned out to be rather futuristic, in the sense that there still remain too many premature components yet to be developed before the total ultrafast pure optical signal processing system will be brought to reality.