DOUBLE-GRATING THIN-FILM DEVICES BASED ON 2ND-ORDER BRAGG INTERACTION

Four coupled-mode equations describing the characteristics of the seco nd-order Bragg interaction are derived for the transverse electric mod e of a dielectric film waveguide with periodic corrugations on both th e film-cover and the film-substrate interfaces. The characteristics of the frequency-selective filter, output coupler, input coupler, and di stributed feedback laser are obtained. Proper choice of the design par ameters leads to a frequency-selective filter radiating neither in the cover nor in the substrate, a highly efficient output coupler radiati ng only in the cover, and an efficient input coupler exciting a guided wave only in one direction. Similarly, in the distributed feedback la ser, a suitable choice of the parameters of the two gratings provides a mechanism for controlling the oscillation characteristics of the las er. The attractive feature of the double-grating design is that the ch aracteristics of the thin-film devices are not very sensitive to small deviations of the grating parameters from their designed values.