Abstract: Various optical functions are generated in accordance with the present invention of a novel broadly tunable monolithic wavelength selective coupler which can be integrated with a gain medium to form a broadly tunable laser. The tunable wavelength selective coupler supports a pair of asynchronous waveguides, an upper waveguide and a lower waveguide, in combination with a phase match course grating for coupling optical energy between said waveguides. One end of the lower waveguide terminates at an output facet. The corresponding end of the upper waveguide terminates in an optical signal absorbing medium. The other end of the lower waveguide is terminated to prevent optical energy from entering the waveguide; and, the corresponding end of the upper waveguide terminates at an input facet.

Abstract: A simple, inexpensive, and reliable technique for substantially preventing the unwanted formation of a surface guiding layer during manufacture of light-guiding structures in LiNbO.sub.3 and LiTaO.sub.3 substrates is disclosed. The technique involves addition of an effective amount of a gaseous hydrogen donor to the processing atmosphere during high-temperature processing. A particularly convenient hydrogen donor is water vapor, which can be added to the atmosphere by, for instance, bubbling of the feed gas through a water column. A partial pressure of more than about 9 Torr of H.sub.2 O has been found effective in the practice of the technique.

Abstract: The response, as a function of frequency, of electrooptic mode converters using comb electrodes has been found to include several peaks at frequencies above and below the desired frequency. These spurious peaks appear to be caused by fringing of the electric field which effectively changes the spatial period of the electrode fingers. To prevent this unwanted coupling, channels have been etched between the comb fingers. The result is to confine the electric field to the narrow region between opposing electrode fingers, thereby minimizing the spurious responses. It also serves to reduce the magnitude of the applied voltage required to produce the same field strength.

Abstract: High speed, integrated optical directional coupler modulators utilize spaces of the order of one micron between waveguides. While one micron delineation of the waveguides can be readily obtained using conformable mask exposure techniques, diffraction effects become significant using thick glass masks required to delineate the electrodes. To overcome this problem, a two-process electrode fabrication procedure is employed. In accordance with the procedure a first pair of electrodes are deposited by a lithographic process. However, this yields a gap between electrodes that is wider than the desired gap. To reduce this distance, the process is repeated with the gap forming region of the mask laterally displaced. The result yields an electrode pattern with the desired spacing and thickness.