Acousto-optics broadly refers to the interactions between optical
(light) waves and acoustic (sound) waves. In engineering,
however, it is now common to refer to acousto-optics more
narrowly as influences of the latter upon the former and various
types of resulting devices of both scientific and technological
importance. Significant influences are possible under certain
situations because the refractive index grating created
by acoustic waves will cause diffraction or refraction of an
incident light wave. Acousto-optics is further branched into
two subareas: bulk-wave and guided-wave acousto-optics. In
the former both light and sound propagate as unguided (unconfined)
columns of waves inside a medium. A great many
studies in the area of bulk-wave acousto-optics since the
1960s have resulted in various types of bulk acousto-optical
devices and subsystems (1–7). In the latter, both light and
sound waves are confined to a small depth in a suitable solid
substrate. This subarea has been a subject of considerable interest
since the early 1970s (8–13) as an outgrowth of guidedoptical
wave (GOW) science and technology (14–20) and surface
acoustic wave (SAW) device technology (21–24), which
had undergone intensive research and development a few
years earlier. The studies on guided-wave acousto-optics have
generated many fruitful results. For example, the resulting
wide-band planar guided-wave acousto-optical (AO) Bragg
modulators and deflectors were widely used in the development
and realization of micro-optical modules for real-time
processing of radar signals, for example, integrated optic RF
spectrum analyzers (13). More recently, integrated AO tunable
filters have been actively explored for applications in
wavelength-division-multiplex (WDM) fiber optic communication
systems (25). This chapter presents a brief review of
bulk-wave acousto-optics and a detailed treatment of guidedwave
acousto-optics with emphasis on the principle of AO
Bragg diffraction, the resulting wave-band optical modulators,
deflectors and switches, RF signal processors and optical
tunable filters, and their applications. It is important to
stress that being free of mechanical moving parts is one of
the unique advantages of AO devices.