Research And Design Of Acquisition Pointing Tracking System For Free-space Optical Communication

Wireless laser communication,also known as the free space laser communication(free space optical communication,FOS),is a kind of wireless broadband communication technology,which using the laser beam to transmit the information in the atmospheric channel.In the wireless laser communication system,acquisition,pointing and tracking(acquisition,pointing and tracking APT)technology is the key technologies for establishing and maintaining communication links.First of all,this paper expounds the characteristics of wireless laser communication system,and it's principle of work and the system composition structure.Structure of the classic APT system is introduced,and details of the beam pointing device and light spot position detection sensor.Combined with the process of wireless communication link establishment and maintain,analyzes the working principle and the working process of the APT system.Secondly,the acquisition time of the three acquisition modes is introduced,and the mode of the beam scanning is analyzed.It is concluded that hexagonal covering is the best scanning method.Combines the advantages of rectangular raster scan and helical scan,the spiral rectangular grating scanning method is proposed.A beam capture system based on radio frequency(RF)assisted link is designed.A scanning method for reverse compensation is proposed.Again,this paper proposed a beam position detection method is proposed for the acquisition,pointing and tracking system in free space optics communication based on expansion of beam propagating atmospheric turbulence?back projection imaging principle and cassegrain system.The method has been analyzed theoretically and experimentally.Transverse deviation and axial deflection of the beams are comprehensive calculated by using the shape and centroid of the beam spot.As a result,we solve the problems in the general method.One is that we cannot distinguish the beam spot fluctuation caused by whether the transverse deviation or the axial deflection.Another is that the transverse deviation cannot be calculated by the general method.The experimental results show that the method can effectively detect the beam alignment state,and finally realize resolution ratio with 2.2?rad in axial deflection and 0.25mm in transverse deviation.In addition,according to the beam detection method proposed in this paper,the two step alignment method is proposed to design the alignment control system and tracking control system.In view of the system experimental platform,adjusting the control parameters,and compensating the gear gap.Finally,the system function verification is completed by building the system experimental platform.Achieve beam capture,alignment,tracking,in the 1.3km distance.The angle tracking accuracy is 34.6?rad,position tracking accuracy is 35mm.