The development of miniaturized and ruggedized optical circuits, containing a number of optical and perhaps also electronic components integrated on the same substrate, and performing useful optical functions - this is the goal of the key technologies for future systems of communication, of instrumenta tion, and of general signal processing; it is expected to combine and to complement the established technologies of microelectronics, optoelectronics, and fiber-optics. Today, after more than fifteen years of research on integrated optics, this goal appears to be almost within reach. The...