Acousto-optic light deflectors using optical activity in paratellurite

Abstract

Light deflector designs which use the anomalously low shear wave acoustic velocity and high acousto-optic figure of merit in single-crystal paratellurite, first proposed by Uchida and Ohmachi, have been made practical by exploiting this material's birefringence to circularly polarized light. Dixon's equations for Bragg interaction in birefringent materials are found to be equally applicable to optically active materials when linearly polarized propagation modes are replaced by circularly polarized modes. For specific ratios of sound-to-light wavelengths, there is a substantially expanded angular range over which Bragg interaction can take place. One effect of this increased range is to permit longer interaction lengths between light and sound, which greatly reduces the acoustic power required. In paratellurite, for visible light, this expanded range occurs for sound frequencies below 100 MHz, in the region of acceptable acoustic loss. Examples of possible designs include a deflector only 3×5×7 mm having a capacity of 500 linearly resolvable spots with a random access time of 10 μsec, with 50% of the incident light being deflected at 35-mW acoustic power.