The Research And Realization Of APT System For Laser Space Communication System

Free space optical (FSO) communication is a very promising way of communicating and will play an important role in the future. This communication technology is applied widely on various occasions for civilian and military use. Acquiring, pointing and tracking (APT) system is the key part to establish precise link between communication terminals of FSO system. APT system and technologies applied in inter-satellite laser communication are mainly studied in this paper.Before establishing the link between communication terminals, an APT system first starts acquiring. Based on satellite orbit, a model is built to show the relative position of satellites, from which the expression for calculating azimuth and pitch angle is derived. Minimizing the uncertain area is benefit for shortening the process of acquisition.A novel design of antenna is proposed in this paper. It receives and transmits light beam by sharing the same optical system, which reduces volume and weight of system. The optical design makes it is possible to integrate the processes of pointing and tracking, which means APT system is able to point laser beam to the target while tracking.As for tracking system, a design adopting bi-axis structure is considered, which consists of coarse tracking loop and fine tracking loop. A charge coupled device (CCD) of wide field of view is used as the coarse tacking detector, while a quadrant device is used as the fine tracking detector. The combination gives full play to each detector's advantages in field of view and speed of response. An acousto-optical deflector (AOD) which specializes in fast and precise beam control is adopted in fine tracking loop. The AOD immensely enhances the bandwidth of fine tracking control loop.Steady-state performance and dynamic performance are incompatible in control system design. To find the way to make a compromise between steady-state and dynamic performance is the ultimate goal of this paper. In the end, the APT system performance is analyzed theoretically, with a conclusion that the increased ratio of bandwidth of fine tracking loop to coarse tracking loop helps to enhance the system stability and improve the capacity of inhibiting control error. An APT demonstration system composed of micro control unit (MCU) is designed and established. Its performance is analyzed and some ways of making improvement is proposed at last.