Abstract

Because of the development of the grafting technique of GaAs films on LiNbO₃ waveguides or glass waveguides, GaAs planar prisms can be fabricated on LiNbO₃ waveguides. To aid in the design of a highly efficient grafted total internal reflection planar prism, we generalize Suchoski's exact numerical technique¹ to include the case of a guided wave incident at variable angles onto a transverse boundary between two slab waveguides that have graded refractive index distributions in the film. Tapered entrance and exit boundaries of the prism are important to keep most of the power confined in the lowest order mode during the entire journey through the prism. Mode conversion is a significant problem at a transition section into a guide that supports many modes. In particular, we find that a parabolic-shaped waveguide horn using a very simple design rule can not be applied to our case because of the asymmetry and the large difference of the index between GaAs film and Ti:LiNbO₃ film. The optimal solution for the taper shape could be obtained by solving the nonlinear optimization problem, which is intractable. Therefore, a thorough investigation comparing the various taper functions is presented in this paper.

© 1992 Optical Society of America