A fast Green's function method for the analysis of IDT's for acousto-optical devices

Surface acoustic wave (SAW) interdigital transducers are key components in X-Y LiNbO/sub 3/ acousto-optical (A-O) devices. SAW interdigital transducers (IDT's) on this substrate exhibit a high spurious resonance that may reduce the A-O efficiency. In this paper we present a detailed analysis of X-Y LiNbO/sub 3/ IDT's based on a fast Green's function method (GFM). In order to correctly evaluate the spurious effects on IDT's performance, we also considered bulk terms of the Green's function. When the GFM is applied to IDT's with general topology and over a wide frequency range, the required computation time can reach quickly unacceptable values for long IDT structures. We developed a new model order reduction technique based on the singular value decomposition (SVD) for the fast generation of the IDT's frequency response. Numerical results for different configurations of X-Y LiNbO/sub 3/ IDT's are in good agreement with measured data and a correct interpretation of the spurious resonance is reported. It is pointed out that bulk wave excitation may be a serious limitation in the design of efficient, wide band IDT's for A-O devices.