Research On Precision Tracking Servo Technology Based On Nutation Mode

Compared with radio frequency communication technology,free space laser communication technology has the advantages of high bandwidth,large amount of information carrying capacity,low quality requirement of power consumption,and good security,etc.,and is widely used in short-distance communication between ground,global communication combined with satellite total reflection technology,and communication between military nuclear submarines.However,in the laser communication system,the receiver is usually a single-mode fiber with a core diameter of only 9?m.In the process of coupling spatial light to the single-mode fiber,the signal light is easily affected by atmospheric turbulence,random Angle jitter and mechanical platform vibration,so that the signal light deviates from the optical fiber end face seriously.Aiming at the above problems,a precise tracking algorithm based on nutation mode is proposed in this paper.By using peak power as feedback,the optical fiber at the receiving end can actively capture and track the signal light,and the coupling efficiency of the receiving end of the communication system is improved.In this dissertation,the basic theory of single-mode fiber coupling system is introduced,and the theoretical extreme value of coupling efficiency is 81.45% under ideal conditions.At the same time,it also studies the variation of coupling efficiency expression under the condition of alignment deviation,random Angle jitter and atmospheric turbulence in the actual system.It is concluded that the radial alignment deviation has the greatest deterioration of coupling efficiency,so it is urgent to design a servo system to correct it.Next,the convergence process of laser nutation and the design principle of tracking algorithm are described,and the overall design scheme of servo system and the selection and performance of related hardware are introduced.Then,the nutation tracking algorithm and the design of servo unit are simulated.The simulation verifies the feasibility of the nutation algorithm,and also simulates the dynamic disturbance suppression effect of the actual system under different equivalent sinusoidal signal inputs.Finally,a single-mode fiber nutation precise coupling system is built,and the coupling parameters selection and dynamic disturbance suppression performance are studied.A large number of static experiments show that when the nutation radius is 1.5?m,the convergence step is 1.25?m,and the number of sampling points is 30,the maximum coupling efficiency is 62.7%.Dynamic disturbance experiments show that the system takes 10 ms from nutation to convergence,and the coupling range is 1.1 mrad;When the disturbance of 1.1mrad and2 Hz is introduced,the system can still reduce the mean square error of the detector's received optical power from 9.91% to 0.81% in the closed loop,it shows that the system has fast dynamic response and strong angle deviation correction ability;Then the coupling performance of the system is tested under different SNR,the results show that when the signal-to-noise ratio is not less than 4.6d B,the nutation coupling system can still converge normally,it shows that nutation algorithm has strong fault tolerance to noise interference.