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.