Filtering properties of multilayered optical tunable couplers and appropriate material composition are theoretically studied. In the structure of ZnS/Ta2O5/Nb2O5 films on a LiNbO3 substrate, narrow bandpass filter of the width 5 can be realized by using acoustic power of several tens mW.

Gyrotropic thin-film waveguides with isotropic top layers are discussed using hybrid modes. The fundamental propagation properties of optical waves and TE-TM mode conversion efficiencies are estimated. When refractive indices of isotropic top layers are equal to those of substrates, 50% TE-TM mode conversion efficiency required for non-reciprocal circuits of optical isolators can be realized with gyrotropic films. From a fabricational point of view, these structures are very useful for constructing thin-film optical isolators because no severe control on film thickness is necessary and film growth of amorphous materials on YIG crystal films is possible for top layers. The design data for non-reciprocal circuits consisting of ZnO/YIG/GGG layered structure are presented from the hybrid mode analysis. The thickness of YIG and ZnO are 3.43 µm and 1.03 µm respectively and the length of the device is 2.28 mm. The non-reciprocal circuits of this structure can be experimentally fabricated by RF sputtering method.

Optical experiments of collinear interaction between two optical guided waves and acoustic waves in multilayered directional couplers are firstly demonstrated. The device consists of ZnS/Ta2O5/Nb2O5 thin films on Y-cut LiNbO3 substrate. Surface acoustic waves of 750 mW at 28.6 MHz switched 90 percent of guided waves between the two waveguides. The bandwidth was 0.6 MHz, which agrees well with the theoretical result. The switching was found to be caused by the accumulation of slight deviation in the optical coupling periodic length along the interaction length. Fundamental optical experiments for this new-type acousto-optic multilayered film device assured the analytic results previously shown by the authors.

Temperature dependence of a SAW-controlled optical wavelength demulti-/multiplexer has been discussed. The device consists of ZnS/Ta2O5/Nb2O5 thin-films on a Y-cut LiNbO3 substrate. The tuning SAW frequency for the optical switching shifted with temperature by -0.20 MHz/. It is theoretically found that a temperature-independent demulti-/multiplexer can be realized when two waveguides possess the similar temperature properties. When the device is used in a narrow wavelength range, the device constituted of nearly degenerated waveguides exhibits small temperature dependence. These results were experimentally verified. In a nearly degenerated device, the temperature dependence was approximately +0.02 MHz/. The other device having small temperature-dependence was fabricated with a ZnS/Ta2O5/Ti-diffused waveguide on a Y-cut LiNbO3, whose temperature dependence was +0.02 MHz/.

Experiments of acousto-optic interaction in slightly nondegenerated couplers are firstly demonstrated with comparison to the theoretical results. The switching mechanism is based on the even-odd mode conversion by acousto-optic effects and on the mode splitting in the separating branch. The device consists of ZnS/Ta2O5/Nb2O5 thin films on Y-cut LiNbO3 substrates of propagation in the X direction. Surface acoustic waves of approximately 0.5 W, 71.2 MHz switch optical power about 90 percent. The frequency characteristics agree well with the theoretical results. These experiment characteristics may give the design base of useful tunable optical filters and multi-wavelength separators.