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Integrated optical circuits are now the subject of research and de-velopment at a number of laboratories. The long-range goal of integrated optics research is to provide arrays of circuit elements capable of combining various discrete operations on guided light beams into sophisticated signal processing and communication devices and systems. It is expected that these devices and systems will take advantage of the inherently wide band-widths available at optical frequencies. They would also be compact, lightweight, economical, and immune to environmental and electromagnetic disturbances. The potentials and advantages of integrated optics are analogous to those realized by integrated electronics technology of the lower frequency spectrum. Considerable amount of work remains to be done, however, before the above ultimate goals are realized. At the present time the approaches taken by the different researchers in the field vary depending on the time frame in which they are working. The most immediately practically realizable systems will probably involve fiber optic communication links with discrete sources (most commonly LED's), direct electrical modulation, existing. detectors, a small number of terminals, and modest bandwidths on the order of tens of megahertz. Such systems have already been demonstrated and are being developed for practical applications. The next generation of systems will most likely involve the so-called "hybrid" approach where information transmission is done in the optical domain and some of the, func-tions are performed in a true integrated optical circuit while others involve discrete components or electronic circuits. In such systems interface elements are of great importance. Finally, the ultimate systems would involve truly integrated optical circuits with integrated and miniaturized components and most of the functions performed in the optical domain. The practical realization of such systems is, however, several years in the future. In the meantime, most of the current research effort is directed toward development of components and technologies compatible with the long-range goals outlined above. This paper reviews the objectives and motivations of the present day integrated optics research and then goes on to discuss recent progress in component and technology development relevant to integrated optics. Special emphasis is placed on the work performed by the several investigators at Hughes Research Laboratories, some of it in collaboration with the Cali-fornia Institute of Technology. Work on fabrication of optical waveguides by various methods such as ion implantation, electron beam lithography, ion beam micromachining, and vapor and liquid epitaxial techniques will be reviewed. Work on various materials such as GaAs, Gai-xAlxAs, GaP, glasses, PMM, etc. will be summarized. Experiments dealing with guide-to-guide coupling (using ion implanted as well as micro-machined three-dimensional guides), gratings for distributed feedback lasers, modulators, and integrated detectors will be discussed.
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