针对非弱导条件下单模-多模-单模(SMS)结构光纤段的理论分析,研究了简单准确的数值模拟方法。利用输入场的泰勒级数展开和多模光纤内电磁场的矢量模式展开,分析了在非弱导条件下SMS结构光纤的多模光纤段中所有模式的传播特性和透射率。基于对模式特征方程的分析,通过合理选择对SMS结构光纤的多模干涉特性有贡献的最少的模式数,计算出每个模式的透射率并与实验结果比较,证明了在单模光纤和多模光纤纤芯精确对准的情况下,利用线偏振径向函数即零阶贝赛尔函数展开多模光纤内的电磁场(标量模型)可以得到很好的数值模拟结果。该结论可有效降低理论研究的复杂性。 Aiming at theoretical analysis of single mode - multimode - single mode (SMS) fiber segments under non - weak conduction condition, a simple and accurate numerical simulation method is studied. The propagation characteristics and transmissivity of all modes in multimode fiber of SMS structured fiber under non-weak conducting condition were analyzed by using Taylor series expansion of input field and vector mode expansion of electromagnetic field in multimode fiber. Based on the analysis of the mode characteristic equation, the transmissivity of each mode is calculated by reasonably selecting the least number of modes contributing to the multimode interference characteristics of the SMS structured fiber. Compared with the experimental results, When the mode fiber core is precisely aligned, good numerical simulation results can be obtained by expanding the electromagnetic field (scalar model) in the multimode fiber using the linearly polarized Bezier function, that is, the zero order Bessel function. This conclusion can effectively reduce the complexity of theoretical research.