Based on Risley Prisms Fine Acquisition, Pointing and Tracking System of the Free-Space Laser Communication Terminal

Fine acquisition, pointing and tracking (FAPT) system of a free-space laser communication terminal should perform a number of functions: to hold the transmitting channel (TX channel) optical axis with a high accuracy (angular seconds), to perform the preemption during information transmission, to compensate for the free-space jitter effect. It is suggested to use Risley prisms as the basis of FAPT system for controlling the laser beam deviation and to solve all the problems listed above. This paper presents a principal optical scheme of the free-space laser communication terminal with Risley-prism-based FAPT system. The optical scheme and operation principle of the FAPT system itself is described in detail, the FAPT system radiation pattern is shown. Using the analysis of the power spectral density of free-space terminal jitter, the required rotation speed of the Risley prisms is substantiated.