Calculation of the number of guided transverse surface acoustic modes for Integrated acoustooptical devices

Abstract

The analogy between the electromagnetic wave equation and the wave equation for the propagation of acoustic waves is used to drive the cutoff lines and the number of guided transverse surface acoustic (Love) modes in stratified piezoelectric media. The combination of these two kinds of waves occurs in integrated acoustooptic devices where the upper layer is made by diffusion of metal atoms into a dielectric substrate. The efficiency of these types of device depends strongly on the overlapping integral of the light mode and the acoustic mode which propagate in the upper layer. In many applications it is important to design the structure parameters in such a way that only a single mode of each kind exists. The present theory describes simple-design tools which enable direct calculation of the proper thicknesses, indices of refraction, the piezoelectric constants of the structure, and the rf operating frequency range. A detailed computation is given for the cases of a two-layer and a buried layer structure.