Studies of the Use of Gyrotropic and Anisotropic Materials for Mode Conversion in Thin-Film Optical-Waveguide Applications

Wave propagation in thin-film optical waveguides using gyrotropic or anisotropic material as substrate is studied. At the film-substrate boundary, the relation between the incident and reflected fields can be expressed in terms of a scattering matrix with matrix elements representing the TE-to-TE and TM-to-TM reflection coefficients and the TE-to-TM and TM-to-TE conversion factors. The property of the scattering matrix is examined, and the condition for continuous and complete mode conversion is derived. Various schemes to achieve complete mode conversion are proposed and the performance characteristics, including the physical dimension and the tolerances in the incident angle and film thickness, for several mode-converting structures are computed and compared. Once the practicability of complete mode conversion is established, it is possible to study the feasibility of practical devices. Various schemes for the realization of such devices as the gyrator, the isolator, the optical switch, and the nondestructive read out are proposed.