Improving Acousto-Optical Interaction by Mechanical Resonators on a Surface

The finite element method is employed to model surface acoustic waves generated by high aspect ratio electrodes and their interaction with an optical wave in a waveguide. With a periodic model it is first shown that these electrodes act as a mechanical resonator, which introduces several confined modes with slow phase velocities because of mechanical energy storage.

The periodic model is extended to a finite model by using perfectly matched layers at the boundaries and the periodic and the finite model are in fine agreement. The finite model is then employed to study the acousto-optical interaction with an optical wave in a waveguide. The difference in effective refractive index is calculated for the case where a positive and a negative electric potential, respectively, are applied to the electrode above the optical waveguide.

This difference is increased more than 500 times using these new types of surface acoustic waves compared to using a conventional interdigital transducer with thin electrodes. Thus, this indicates a way to improve acousto-optical interaction for integrated modulators.