Status of integrated optics and some unsolved problems

There have been recent dramatic advances in guided‐wave optical devices and although only a few functions have so far been integrated onto a single substrate, the individual devices are being applied and there is promise for integration in the future. The most dramatic advances have occurred with respect to semiconductor lasers, with GaAs and GaAlAs lasers now operating at room temperature with long life. A variety of techniques, including chemical etching, liquid‐phase epitaxy and ion implantation have been used for fabricating waveguides on these materials. Similar advances have been made with respect to guiding and electro‐optic effects on LiNbO 3 and LiTaO 3 . Devices discussed in the paper include the guides themselves, junctions and bends, switches or modulators, the laser sources, and detectors. Many of the electromagnetic problems encountered in the analysis of these devices are inhomogeneous and anisotropic and some are nonlinear. Mode conversion is a common problem, and sensitivity to polarization must be kept in mind.