Multi-gigabit Free-space Optical Communication System with Bidirectional Beacon Tracking

The performance and design highlights of a multi-gigabit free-space optical communication system with fast and accurate beacon tracking are described. In order to achieve high data-rate as well as eye-safety, transmitting laser beam at a 1552 nm wavelength is collimated to be near diffraction limited and the beacon tracker, operated at a 980 nm wavelength with a Si quadrant photodetector, a miniature fast steering mirror and a wideband proportional-integral-derivative (PID) servo controller, is used to detect the receiving beacon direction and to point the transmitting laser beam to the opposite terminal. A preliminary result of a 10-Gbps bidirectional transmission experiment over 1-km distance at Waseda University and the corresponding link analysis are also presented.