Agile acousto-optic tracking system for free-space optical communications

Laser communication is viewed as an enabling technology with great potential in both long-range and "last-mile" applications, serving the needs of individual subscribers, corporate offices, military, and possibly deep-space missions. Indeed, lasers allow for concentration of energy within tightly focused beams and narrow spectral intervals, thus offering high throughput, information security, weight and size of components, and power requirements that cannot be matched by rf systems. A key challenge is that high data rates should be complemented by high-precision wide-bandwidth position control of a laser beam. In many applications, the ability to maintain a link is affected by the complex maneuvers performed by mobile communication platforms, resident vibrations, and atmospheric effects. This work is focused on the application of acousto-optic technology as an alternative to electromechanical devices, which addresses the tracking problems encountered under such conditions. With the realization that an acousto-optic Bragg cell is only a component of the entire system, which should perform complex tasks of pointing and tracking of the remote terminal, we present an attempt to consider this problem from the "systems" point of view. We present the developed electro-optical laboratory prototype, show synthesis of the control system, and feature experimental results that demonstrate excellent tracking performance.