在空间激光通信应用中, 空间光与单模光纤的耦合效率是影响通信系统性能的重要因素。考虑大气湍流会降低激光与光纤的耦合效率, 本文从湍流强度与光学系统分辨率之间的关系出发, 研究了大气湍流对光纤耦合效率的影响, 导出了接收口径、系统焦距、入射光波长、接收光纤半径、大气相干长度等与单模光纤耦合效率之间的关系。提出了两种在湍流环境中提高光纤耦合效率的方法。 方法一是在外界湍流强度发生变化时, 通过改变耦合系统焦距, 使耦合效率保持在较高值; 方法二则是采用锥状光纤接收来提高耦合效率。最后对提出的方法进行了分析、仿真和室外耦合效率测试, 验证了所提出的改善耦合效率方法的有效性。

In high speed free space optical communication systems, the efficiency that a laser beam is coupled into a single-mode fiber is an important factor. However, the laser propagation through atmospheric turbulence degrades the fiber coupling efficiency. According to the relation between turbulence intensity and optical system resolution, this paper explores the effect of atmospheric turbulence on fiber coupling efficiency, and derives the relationship of the receiving aperture, focal length, the wavelength of incident light, fiber radius and atmospheric coherence length with the single mode fiber coupling efficiency. Two methods were proposed to improve the fiber coupling efficiency in a turbulence environment. The first method is to maintain the coupling efficiency to be the maximum by adjusting the focal length of the coupling system when turbulence environment is deteriorated. The second one is to use a taper fiber in receiving end of the focal plane to improve the coupling efficiency. Finally, corresponding analysis, simulation and a coupling efficiency experiment at outdoor were performed, and it verifies the effectiveness of the improved method for fiber coupling efficiency.