Abstruct-The theory, technology, and applications of bulk-wave acoustooptic devices are reviewed. A coupled wave analysis for the acoustooptic interaction in an anisotropic medium is presented. The bandwidth and angular aperture characteristics of acoustooptic devices are discussed in terms of simple phase mismatch considerations. The present status of acoustooptic materials and transducer technology is summarized. The characteristics and applications of acoustooptic devices, including deflectors, modulators, and optical filters, are discussed.

I. Acoustooptic Devices and Applications

The physics and technology of acoustooptics are reviewed mainly from the standpoint of designing laser-beam deflection devices and their applications. The ultrasonic light diffraction theory in a form useful for device application is outlined, beginning with the well-known Raman-Nath equation and covering both normal and abnormal types of Bragg reflection. Various acoustooptic materials are evaluated on the basis of two main factors, i.e., acoustooptic figures of merit and acoustic attenuation, as well as availability and optical quality. Guidelines for the selection of materials are discussed in some detail, although they are still insufficient for the complete prediction of new suitable materials. Elements of the acoustooptic light deflector are presented, and the importance of the fabrication techniques is stressed. As examples of the performance characteristics of the deflector, those of TeO 2 [001] longitudinal-wave and [110] shear-wave deflectors are described. Applications of the deflector to several kinds of apparatus and systems are considered on the basis of the present and the future states of the art.

Acoustooptic deflection materials and techniques

An introduction is given to the principles of integrated optics and optical guided-wave devices. The characteristics of dielectric waveguides are summarized and methods for their fabrication are described. An illustration is given of recent work on devices including directional couplers, filters, modulators, light deflectors, and lasers.

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An Introduction to Integrated Optics

Tellurium dioxide (TeO2) nanowires with a tetragonal structure have been grown by thermally evaporating tellurium metal at 400°C in air. The nanowires produced have diameters ranging from 30to200nm and have lengths of several tens of micrometers. Gas sensors were fabricated using the obtained TeO2 nanowires. The sensing behavior to NO2, NH3, and H2S gases at room temperature showed typical characteristics of a p-type semiconductor. The results demonstrate the potential to develop TeO2 nanowire based gas sensors with low power consumption.

Room temperature gas sensing of p-type TeO2 nanowires

Noncollinear acoustooptic tunable filters using TeO(2) crystals are described. An anisotropic Bragg diffraction is studied applying simple design expressions to a tilt type in which an acoustic wave is launched a little off the [110] axis. Tuning property, filter bandwidth, angular aperture, required acoustic power, deflection angle, divergenceless configuration, and rapid spectrum scanning have been discussed. These filter properties have been confirmed with measurements using three kinds of filter devices: a basic type, an acoustically enhanced type, and a large angular aperture type. A 5-A bandwidth at 4000 A was obtained by slow scanning. A 32-A separation at 4000 A was observed by a rapid scanning of 0.5 msec throughout the visible region with an extremely low electric drive power.

Acoustooptic TeO(2) tunable filter using far-off-axis anisotropic Bragg diffraction.

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.

D. L. White

Papers

Acousto‐optic light deflectors using optical activity in paratellurite