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: Orthogonally polarized waves are more effectively decoupled in a waveguide that is fabricated in a manner so as to deliberately enhance stress-induced birefringence. This characteristic is accomplished by introducing a geometrical and material asymmetry in the preform from which the optical fiber is drawn. Three methods of preparing the preform are disclosed. Optical waveguides capable of transmitting power with only one direction of polarization are desirable for use with integrated optical devices which are polarization sensitive.

Abstract: Optical signal processing devices, primarily intended for use in integrated optical communication systems, include 3 dB coupled strip guide directional couplers. Each coupler is formed in a body of electrooptic material and includes electrodes bracketing at least one of the guides in the coupled region. Each coupler is fabricated so as to be overcoupled (i.e., greater than 3 dB coupling) when the coupling is synchronous. Voltage bias, supplied to the electrodes of each coupler, produces sufficient asynchronism to independently adjust each coupler to the desired 3 dB coupling condition. Permutation switches are produced by including a switchable phase shifter between two couplers. Channel drop filters are produced by including reflection gratings between two couplers. Differential phase detectors, for a pulse code modulation system, are produced by including a selected path length difference between the two strip guides connecting two couplers.