Thin dielectric waveguide with a phased array of two gratings on its surfaces

Abstract

The deexcitation and the excitation of the transverse electric (perpendicular polarization) and the transverse magnetic (parallel polarization) guided modes in a thin-film planar dielectric waveguide sandwiched between a cover and a substrate (two different dielectrics) are considered. There are two gratings, one on each surface of the film, with the same grating wave number but with different relative amplitudes and phases. The three governing equations are derived by a quasioptical technique, and the reciprocal property and the power conservation requirements are examined. An output coupler with no radiative leakage in the substrate and a practical input coupler with the incident beam in the cover only and with a high input coupling efficiency are designed with a suitable choice of the grating depth ratio and the lateral phase shift. An output coupler can be achieved with no radiative leakage either in the substrate or in the cover by an appropriate choice of film thickness and the grating parameters. This configuration of the output coupler is used in the development of a grating polarizer with the output either in the perpendicular or in the parallel polarization. Selected numerical results are presented to illustrate the important characteristics of the output and the input couplers and the polarizers as well as the sensitivities of the performance of these devices to small changes of the physical parameters about their designed values.