Abstract

Channel waveguides with minimum mode size, and electrode patterns that maximize the overlap integral between the guided optical field and the applied modulating field are essential for efficient operation of Ti diffused LiNbO₃ modulators, switches and other active guided wave devices. Previous efforts have concentrated on improving the coupling efficiency of Ti:LiNbO₃ waveguides to single mode fibers. A total fiber-waveguide-fiber insertion loss of 1 dB at 1.32 μm in a z-cut LiNbO₃ crystal was achieved [1] by carefully selecting the fabrication parameters so that the TE and TM modal width and depth nearly matched that of a single mode fiber, specifically for guides with Ti strip widths in the range of 6 -10 μm. These waveguides, however, are not quite suitable for efficient active, guided wave device operation, due to their large mode size. Instead, minimum mode size waveguides are required for the maximization of the overlap integral between the optical and modulating fields. It is recognized that the coupling of suchwaveguides to single mode fibers will result in a large mode mismatch loss. In order to reduce this coupling loss to a reasonable value, it is necessary to incorporate a tapered transition [2] between the small mode size LiNbO₃ guide and the single mode fiber.

© 1987 Optical Society of America