Research Of Simultaneous Tracking And Communications Based On A Quadrant Avalanche Photodiode Detector

With the advantage of wide bandwidth,high communication rate and strong anti-interference ability,space laser communication has become one of the most effective ways to solve the problem that the bandwidth of radio communication is close to the limit and the communication rate is difficult to be raised.In order to meet the requirement of short distance and low communication rate for near-ground atmospheric laser communication,the technology of simultaneous tracking and communication based on a quadrant avalanche photodiode detector has great significance for the miniaturization of laser communication terminal.Compared to traditional space laser communication system that tracking and communication is separated and the coaxiality of tracking optical axis and communication optical axis is strict,the multiplexing technology only use single detector to complete tracking and communication which could simplify the structure of terminal and reduce system power consumption effectively.This paper introduces the application status of QD in space laser communication,analyzes the precondition and main characteristics of composite detection,describes the principle of spot position detection on four-quadrant detector and the influence of spot size,spot position,background light,spot energy distribution,dead zone,signal-to-noise ratio(SNR)on spot centroid detection,proposes the scheme of composite detection,designs the hardware circuit,including the laser transmitting and modulation unit,photoelectric conversion and front end signal processing unit,tracking servo control unit,communication demodulation unit.Finally,the experimental system is established.The communication rate is 10Mb/s,the detection sensitivity is-35.4dBm,the bit error rate is 10-6 under the condition of Manchester code,Intensity Modulation/Direct Detection.The minimum position resolution of the spot position detection is 2um,the angular resolution is 0.8urad,and the tracking accuracy of the closed-loop tracking system is 2.5urad.This paper demonstrates the feasibility of using QD for simultaneous tracking and communication,which lays the foundation for the design of the whole laser communication system.