DEVELOPMENT OF A FINE TRACK SYSTEM FOR THE AEROSPACE LASER COMMUNICATIONS TESTBED

In a laser communications terminal, a received beam can be coupled into a single-mode optical fiber for demodulation by the communications subsystem. Coupling free-space light into an optical fiber requires precise control that can be adversely affected by local jitter disturbances, which can generate excessive optical loss that might disrupt communications. To maximize received power in-fiber, we have designed and built a closed-loop fine tracking system that directs and locks a received laser beam onto the core of a single-mode fiber. This fine tracking system operates by applying a small angular nutation to the received light, generating a pointing error signal that can be extracted by analog demodulation of the power. A fast-steering mirror controller compensates for the measured pointing error. This paper will discuss the development and characterization of this system.