Experimental Study On Non-Coaxial Alignment Of Beam In Wireless Laser Communication

Wireless optical communication is a communication method that uses the beam as the carrier for data transmission.Acquisition Pointing and Tracking(APT)technology is the precondition to ensure the normal communication of the link of wireless optical communication system.In this paper,a two-dimensional reflector is used to realize the non-collinear alignment of the beam.By using the camera at the transmitter to target the image of the long-distance two-dimensional reflector,the long-distance alignment of the beam with the two-dimensional reflector at the receiver is completed,and at the receiver,the non-coaxial alignment of the beam with the receiving antenna’s line of sight is completed through the control of the two-dimensional reflector.In this paper,based on wireless optical communication,non-coaxial alignment technology of light beam in APT system is studied experimentally.The main research contents are as follows:1.Two-dimensional reflector with large aperture,high resolution and large travel is used as the control core of the tracking system.The input and output data of the tracking system are measured,and the parameters of the tracking system model are identified by the least squares method.The exact transfer function of the tracking system is obtained,and the response curve is analyzed.The trajectory of the beam when the two-dimensional reflector scans the beam at the receiving end is studied,and the proportion,integral,and so on are used.The differential control algorithm compensates for the error of the tracking system during the spot tracking process.2.The effects of atmospheric turbulence on beam intensity flicker and angle of arrival fluctuate at the receiving end with the increase of beam transmission distance at different atmospheric turbulence intensities are analyzed theoretically.The angle of arrival fluctuates,which makes the spot on the focal plane jitter,so that the spot image detected by the infrared camera is overlaid with random noise,which can be obtained from the propagation and scattering in random media.The statistical characteristics of speckle noise caused by light intensity flicker and angle of arrival fluctuation are approximately normal distribution,so Kalman filter algorithm is used to eliminate the influence of noise on the measurement error of image detection algorithm.3.In this paper,two-dimensional reflector and Kalman filter image detection algorithm are used as the core of APT system,and then a field experimental platform of 1.3 km,4.1 km,10.3 km experimental link is built.The performance of Kalman filter image detection algorithm and the feasibility of using two-dimensional reflector as the executing mechanism for speckle tracking are verified.The experimental results show that the difficulty of beam alignment in APT system can be reduced by using the two-dimensional reflector proposed in this paper.Compared with traditional spot image detection algorithms,the kalman filter algorithm proposed in this paper can reduce the laser transmission distance at 1.3,4.1,10.3 km.The root mean square error of the spot in the pitch direction decreased from 0.740,2.537 and 7.256 pixels~2 to 0.683,1.792 and 4.756 pixels~2,and the root mean square error of the spot in the horizontal direction decreased from 0.481,2.131 and 5.932 pixels~2 to 0.463,1.471 and 4.362 pixels~2.