Possibility of Switching and Steering Surface Waves by Nonlinear Mixing in Anisotropic Media

It is known that when two acoustic surface-wave beams intersect in a suitably anisotropic medium, sum and difference frequency beams are generated parametrically if both frequency and phase velocity are matched. Using coupled-mode theory we show that this effect can occur even in the presence of imperfect phase matching. In consequence it should be possible to produce sum and/or difference frequency beams over a continuous range of angles, with the direction controlled by the ratio of the input beam frequencies. Computed input and output beam angles are presented for a number of materials and device applications are discussed.