Spatial tracking using an electro-optic nutator and a single-mode optical fiber

Recently, the potential advantages of using single-mode optical fibers within free-space laser communication systems has been recognized. Of particular importance within an optical receiver is the spatial tracking system, which must couple the received signal into a single-mode optical fiber in the presence of environmental disturbances. Because optical beamwidths are small (microrad) and typical disturbances can be large (mrad), this requirement makes the design of the spatial tracking subsystem an important and difficult part of an optical receiver. Previous systems have utilized mechanical techniques for nutating the tip of the receiving fiber to derive tracking information. A new technique, based on using a fixed fiber and an electro-optic beam deflector, is proposed. Design considerations and experimental results are presented.