Research On Single Mode Fiber Coupling Algorithm Based On Energy Feedback

In recent years,with the development and popularization of mobile Internet,Internet of things and other applications,people's demand for communication capacity is increasingly high,and the precious electromagnetic spectrum is cumulatively crowded,which makes people turn to seek for new technologies to expand the existing radio technology.Free space optical communication,also known as laser communication,has attracted extensive attention from research institutions and scholars around the world due to its advantages combining both wireless communication and optical communication.Laser communication has the advantages of high bandwidth,small volume and quality of terminal,no need of spectrum permission,good security and confidentiality,but many technical difficulties occur as well.During the process of laser communication,the receiving terminal generally need to couple space beam into single mode fiber.Because the diameter of single mode optical fiber core is only a number of microns,external disturbance,such as atmospheric turbulence and platform jitter easily causes the received focus spot migration on the optical fiber end plane,which greatly reduces the optical energy coupled into single mode fiber and seriously affect the quality of communication.So maintaining optical coupling efficiency is the basis to establish laser communication link,and the fiber coupling algorithm is the kernel of the coupling system.Aiming at fiber coupling algorithm in laser communication,this paper sets up a single-mode fiber coupling system based on fast steering mirror and takes optical power coupled into the fiber as feedback to study two optical fiber coupling algorithms,laser nutation and stochastic parallel gradient descent(SPGD).By theoretical analysis,simulation research and experimental verification,this thesis summarizes the relationship between the characteristics of two algorithms and respectively their parameters,compares the performance of two algorithm and provides the basis for the engineering application of fiber coupling algorithm.The maximum coupling efficiency under ideal condition is analyzed,and the maximum coupling efficiency is 81.45% when the coupling coefficient equals 1.12.The effects of alignment errors of three kinds of optical fibers,lateral deviation,axial deviation and angle deviation,on coupling efficiency are studied.It is demonstrated that the deviation of the incident angle can be equivalent to the lateral deviation of the focal plane,which provides a theoretical basis for the design of single-mode fiber coupling system based on fast steering mirror and experimental study.The flow of laser nutation and SPGD algorithm are described respectively,and the principle of SPGD algorithm and its advantages over other gradient descent methods are proved.The simulated wavefront is built based on Zernike polynomial,and the static error correction simulation of the two algorithms is carried out to prove the effectiveness of the two algorithms.The simulation is carried out based on different parameter combinations,and the relationship between parameter values and algorithm performance is preliminarily obtained.Based on the single-mode fiber coupling experimental system,static deviation correction and dynamic disturbance correction experiments are carried out for the two algorithms respectively.After a lot of experimental studies,the variability rules of nutation radius and sampling times on the performance of nutation algorithm are obtained.The effects of random perturbation amplitude and gain on the performance of SPGD algorithm are also discussed.In dynamic correction,for 300 ?rad sinusoidal disturbance,under the suppression ratio criterion of-10 dB,the suppression bandwidth of nutation algorithm is 2.5 times wider than SPGD algorithm.