Phase sensitive optical measurements and numerical simulations of a fan-shaped filter

Acoustic field profiles within a dual-track fan-shaped SAW filter on a 112° LiTaO₃ substrate have been studied in detail with our heterodyne laser interferometer. The experimental results are compared to extensive numerical simulations utilizing discretization of the filter into elementary cells. The experimental results and simulations show the existence of a phase difference between the acoustic main beam and its side lobes. Also, the wave fronts are tilted with respect to the propagation direction. The unidirectionality of the launching transducer and the absorption at the receiving transducer are determined experimentally. The simulations reproduce not only the amplitude fields, but also the phase fields with excellent accuracy when compared with the phase sensitive laser interferometric measurements.