Surface acoustic wave interaction with polarized light

Abstract

It is of primary importance for acoustooptic signal processors to have high efficiency and wide bandwidth and, hence, enhanced dynamic range. In those devices employing the side entry technique, an unguided optical beam enters a substrate at grazing incidence. It is then totally internally reflected from the top surface on which a surface acoustic wave Is propagating. As it propagates laterally through the substrate just beneath the surface, the optical beam is Bragg diffracted by the surface acoustic wave. Taking into account this particular interaction geometry, the Guassian nature of the optical beam and the decay of the surface acoustic wave, the interaction efficiency and incidence angular bandwidth for both p- and s-polarized light are calculated. The theoretical results are compared to experimental observation, which shows that for a YZ-LiNbO3 substrate, p-polarized light has a higher diffraction efficiency over a wider incidence angular bandwidth than s-polarized light, a fact that can be used advantageously to enhance the dynamic range in these acoustooptic devices.