Acousto-optics and acousto-optical components

Acousto-optics refers to the science and techniques by which an acoustic wave can be used to alter the propagation of an optical wave. The volume acousto-optic components described in this article receive a radio-frequency electrical signal as input, which, via a piezoelectric transducer, enables the generation of an acoustic wave. An incident optical wave, often from a laser source, is diffracted by the index grating accompanying the acoustic wave due to the photoelastic effect. The diffraction efficiency, which can reach 100% under optimum conditions, is accompanied by an optical frequency shift equal to the acoustic frequency. Acousto-optic components are commonly used to produce intensity or phase modulators, frequency shifters, programmable deflectors and tunable filters. The optical range covered extends from ultraviolet to mid-infrared, while acoustic frequencies are of the order of a few tens of MHz to a few GHz, with no theoretical limit other than optical and acoustic propagation losses. This article first presents the fundamentals of acousto-optic interaction modeling, limiting itself to the simplest case of volume plane-wave interaction, but considering the effects of optical and acoustic anisotropy in the crystals commonly considered, notably paratellurite. Secondly, a technical description of each of the major classes of devices is presented: modulators, deflectors and tunable filters. For each of these applications, the essential design rules are explained, and the characteristics and limitations are illustrated with examples.

At the end of the article, readers will find a glossary and a table of symbols used.