Active pointing control for short range free-space optical communication

Abstract

Maintaining optical alignment between stations of a free-space optical link requires an active pointing mechanism to persistently aim an optical beam toward the receiving station with an acceptable accuracy. This mechanism ensures delivery of maximum optical power to the receiving station in spite of the relative motion of the stations. In the active pointing scheme proposed in the present paper, the receiving station estimates the center of the incident optical beam based on the output of a position-sensitive photodetector. The transmitting station receives this estimate via an independent communication link and uses it to accurately aim at the receiving station. The overall mechanism which implements this scheme can be described in terms of a diffusion process which modulates the rate of a doubly stochastic space-time Poisson process. At the receiving station, observation of the space-time process over a subset of $\mathbb{R}^2$ is provided in order to control the diffusion process. Our goal is to determine a control law, measurable with respect to the history of the space-time process, which minimizes a quadratic cost functional.