Abstract: The performance of the spatial pointing, acquisition and tracking system for free-space laser communications largely depends on the accuracy of estimating the angular coordinates of an incoming laser beam on the optical communication terminal. In this paper, the authors propose a novel angular discriminator for spatial tracking in free-space laser communication systems. The optics design of the angular discriminator is based on the use of a Fabry-Perot Etalon. The principle of operation of the angular discriminator is to transform the angular difference between two laser beams into electrical phase difference between the IF component of two coherently detected photocurrents. The electrical phase difference is thus easily estimated by a post-detection electronic processor. The angle to phase conversion of the Fabry-Perot Etalon has been verified by an experiment. The advantage of using the novel angular discriminator for spatial tracking in free-space laser communications is that the mean and standard deviation of the angular tracking errors are small, therefore, the update interval in steering the signal beam in the range of MHz is possible. The angular span can be made larger than one beamwidth in order to minimize the probability of re-acquisition. Two of the photodetectors used for spatial tracking form a dual-detector coherent receiver for communications. Therefore, the spatial tracking sensors and the communication photodetectors are integrated into a single system. The novel angular discriminator can be used for spatial acquisition as well.!
展开▼
