<title>Acousto-optic deflector for free-space laser communications</title>

Abstract

A technique is developed to steer the transmit laser beam for free-space laser communications (lasercom) using a 2-dimensional acousto-optic (AO) Bragg cell deflector. Important characteristics of the AO Bragg deflector include high angular resolution, fast switching speed, high electrical and optical efficiency, and high reliability with no moving parts. A demonstration transmitter terminal was developed to steer a laser over a range of 360 degree(s) X 36 degree(s). Several unique capabilities are provided by the AO deflector which are not possible with conventional steering mirrors. For example, multiple simultaneous beams can be independently steered anywhere within the total steering range. Also, the AO deflector can produce variable defocus (zoom) that increases the divergence of the beam to over 10 times the diffraction-limited beam width. A direct-digital- synthesizer (DDS) was developed to produce stable and fast switching frequencies for input to the AO deflector. All of the beam control and diagnostic functions for the demo transmitter are provided by a menu-driven PC486-33 computer program.