Research On The High Precision ATP System In Satellite-to-earth Quantum Communications

Quantum communications is becoming a hot subject of communication field in recent years.Based on the principle of quantum theory, this technology has absolute secrecy andpreponderances to other communication mode. Current quantum communication system alwaysuse optical fibres for its transmission channel. However, the communication distance is limitedfor the attenuating characteristic of optical fibre. Space-based quantum communication,especially, satellite-to-earth quantum communication slips the leash of optical fibre and becomesthe best choice for global quantum communication network. This research has become the coreareas of the competitions in science and technology between countries. During the space-basedquantum communication, there is a relative motion and link interference between the terminals.What’s more, the satellite platform also has vibrations. So there must be a the high precisionacquision, tracking, pointing system (ATP system) for establishing and stabilizing thecommunication link.Founded by the Knowledge Innovation Project of the Chinese Academy of Science, thisthesis carries out research on tracking and pointing techniques in satellite-to-earth quantumcommunication ATP system. In this thesis, the principle and demand of satellite-to-earthquantum communication ATP system is first analyzed. From this analysis the requirements ofbeacon detection for the system is gotten. It also the design of ATP system, especially, accuratetracking system is discussed. A demonstration platform is built, and the design principle isverified by this platform. As one of the main work, the research also focuses on laser beacondetection and processing technology of spaceborne ATP system. A high frame-rate and highprecision space-based dececting camera has be developed. The thesis also researches severaltechniques for raising the positioning accuracy of spot-decting camera. Pointing accuracy of ATPsystem is studied. A testing platform is designed for our ATP system is developed, and the ATPsystem which is developed by the design principle of this thesis gets extremely high precision.Some designs for improving pointing accuracy are put forward and verified.The innovations of this thesis are represented as follows:1）This thesis discusses the requirements, operational principle and performance ofsatellite-to-earth quantum communication ATP system in detail. Spaceborne ATP systemdesigning principle is studied. For proving this principle of high precision ATP system, ademonstration platform is built.2）On foundation of theoretical analysis and the demand of beacon detection for spaceborne ATP system, design parameters of the laser beacon detection cameras of ATP system for quantumcommunication between satellite and ground are specified. A beacon detection and processingsubsystem is designed by using CMOS detector(STAR1000) and FPGA. For the camera:detection frequency faster than2kHz, detection resolution better than1rad, dynamic range isabout50dB.3）In order to raising the precision of ATP system, this thesis research some methods fromthe angle of positioning accuracy of detecting camera. A test method for get the positioningaccuracy of detecting cameras has been created. Several factors in positioning accuracy areannalyzed and the effect is simulated. Some techniques for improving positioning accuracy areput forward which contrapose satellite-to-earth quantum communication ATP system.4）Several real-time techniques are explained in this thesis: According to the theory ofgradient measure, the real time method of defective pixel check and correction is achieved. Thecamera gets the ability to detect weak signals by applying nonuniformity correction in real time.The research and design of adaptive-exposure to adapting exposure time make the spacebornecamera could restrain the interference of communication link.5）The effect for pointing error is analyzed theoretically, and a high precision test systemwith0.1rad resolution is designed. According to the test and correction with this test system, anATP system developed by the theory of this thesis gets a high precision (better than3rad).The research achievement of the thesis has resolved the key technical problems of the highhigh precision ATP system in satellite-to-earth quantum communication, and provides richexperiences for the project courses.