Self-collimating surface acoustic waves on multilayer structures

There has been growing interest in recent years over the investigation of bulk acoustic waves (BAW) which propagate along certain directions in anisotropic crystals with a minimum of diffraction. One application of these BAWs is for multichannel acousto-optic devices. The fact that the beams propagate with the minimum diffraction implies that the channels in such a device can be closely packed. In this paper we present a methodology whereby self-collimating surface acoustic waves (SAW) can be engineered on surfaces where the substrate itself does not exhibit this behavior. We discuss the specific case of a ZnO layer on (001)-cut <;110>-propagating GaAs for which a fair amount of slowness surface data exists. Finally, using angular spectrum of plane waves (ASPW) diffraction theory we present beam propagation data which substantiates the claim that the beam on such a multilayer structure can propagate without changing its shape.