Adaptive Single-Mode Fiber Coupling Method Based on Coarse-Fine Laser Nutation

One of the major restrictions of the free-space optical communication systems is the limitation of single-mode fiber (SMF) coupling efficiency that impacts the system performance. In this paper, an adaptive coupling method for optical communication system based on coarse-fine laser nutation technique was presented. The scanning strategy and algorithm were set up and experimentally examined. The experimental results demonstrate that the coarse-fine laser nutation technique is capable of achieving a good coupling efficiency even the beam spot and the SMF do not coincide with each other at the start. The SMF center calculation accuracy of coarse and fine scanning stage were 0.25 and 0.01 μm, respectively. And the average coupling efficiency of the system can increase from 0.351 in open loop to 0.624 in closed loop under a simulated atmospheric turbulence condition, the offset compensation error was 0.1245 μm when turbulence induced. Finally, some factors influencing the systems were also discussed.