本文以一种离散、等间距的随机耦合模型来模拟实际单模光纤。从理论上证明了在具有随机耦合的单模光纤中,偏振度并不随光纤总长度的增加而趋向于零。数值计算表明偏振度的系综平均值随光纤总长度的增大将趋于一个非零的渐近值,此值与随机耦合强弱及光源谱宽、光纤双折射、耦合点的空间频率有关。 In this paper, a discrete, equally spaced stochastic coupling model is used to simulate an actual single-mode fiber. It is theoretically proved that the degree of polarization does not tend to be zero with the increase of the total length of a fiber in a single-mode fiber with random coupling. The numerical calculation shows that the ensemble mean value of polarization tends to a non-zero asymptotic value as the total fiber length increases, which is related to the intensity of random coupling, the spectral width of the light source, the fiber birefringence and the spatial frequency of the coupling point.