Significance   Space laser communication has the advantages of large capacity, high bandwidth, strong confidentiality and great anti-electromagnetic interference ability. It is widely used in the field of space communication. Laser communication is one of the important ways to realize large capacity secure communication between space and earth, starry sky, interspace, air and sea, air and air links. It has become a research hotspot for realizing space communication links at present. The fast and stable space laser communication needs to be based on high performance ATP (Acquisition, Tracking and Pointing) technology. In order to achieve the purpose of optical signal acquisition, the working direction of the transmitter and receiver needs to be changed. However, due to orbit and energy constraints, space targets and spacecraft cannot change their attitude and position at will. The application of beam deflection technology can solve this problem well.

  Progress   In the study, the research progress of 6 types of beam deflection technologies, mechanical and non-mechanical, is systematically summarized. According to the deflection characteristics of different technologies, the characteristics of each type of beam deflection technology are compared and analyzed from the aspect of key performance index. Table 1 is used to visually compare and analyze the key index that affect the deflection performance. In addition, the research progress of electro-optical deflection technology in recent years is analyzed. KTN (Potassium Tantalate Niobate） electro-optical crystal has good quadratic electro-optic effects and can achieve better deflection performance compared with other deflection technologies. By following up the progress of major research institutions at home and abroad, such as, NTT (Nippon Telegraph and Telephone) in Japan, University of Pennsylvania in the United States, Shandong Academy of Sciences, Harbin Institute of Technology, Nankai University, etc., sorted out their own research context of the main line, summed up and analyzed the problems to be solved. Then, the development trend and prospect are presented from the perspective of space application performance requirements.

  Conclusions and Prospects   Comparing various beam deflection technologies, it is found that mechanical beam deflection technology has a large deflection Angle, but it is difficult to meet the high requirements of miniaturization and lightweight for space laser communication in spaceborne environment due to its complex structure, large volume, high energy consumption and easy wear. In the non-mechanical deflection technology, the acoustic and optical deflection technology has high deflection efficiency, but it has a strong dependence on the incident wavelength and angle of the beam. The liquid crystal deflection technology has low power consumption and large deflection angle, but the response speed is slow, and it is difficult to meet the task requirements of large-bandwidth transmission. The beam deflection device based on electro-optical crystal has the advantages of continuous deflection angle, fast response speed and high sensitivity. It is considered to be one of the leading directions for realizing high-speed optical deflection technology. Among all kinds of electro-optical materials, the electro-optical deflection device based on KTN crystals have many advantages, such as large angle deflection, fast response speed, high deflection efficiency and deflection accuracy, and wide bandwidth operation, etc., which have more potential applications in space laser communication and other fields. However, there are still some shortcomings: 1) The uniformity of the components in KTN crystal is a major factor affecting the deflection performance. At present, the preparation of KTN crystal with uniform components cannot be realized. 2) The regulation mechanism of beam deflection by polar nanoregions in KTN crystals near Curie temperature is not clear yet and needs further study. In the future work, on the one hand, the crystal growth method can be studied, and KTN crystals can be grown according to the growth law of other crystals. On the other hand, the microscopic deflection mechanism of KTN crystals should be gradually studied to find the internal causes affecting the beam deflection performance.