Fine pointing control for optical communications

Free-space optical communications requires precise, stable laser pointing to maintain optimal operating conditions. This paper describes the software and hardware implementation of the fine pointing control based on the Optical Communications Demonstrator architecture. The implementation is designed to facilitate system identification of the fast steering mirror mechanism. Models are derived from laboratory testing of two fine steering mirrors that are integrated into the fine tracking loop. Digital controllers are then designed to close the tracking loop using optical feedback. Results of the fine pointing control performance show an improvement of 20% in the jitter rejection bandwidth over previous experiments. A discussion of the computer delay and limited processing bandwidth in this particular implementation are included.