论述了SMS(单模-多模-单模)光纤结构的多模干涉基本理论, 利用FD-BPM(有限差分光束传播法)对渐变折射率多模光纤和阶跃折射率多模光纤进行数值模拟, 将自聚焦位置、激发模式等特征进行对比, 给出渐变折射率多模光纤的优点。利用自聚焦效应, 对渐变折射率多模光纤的聚焦和发散作用进行了理论分析, 以较短的长度充当透镜的功能, 并总结了现阶段的主要应用。

A multimode interference basic theory of singlemode-mutlimode-singlemode (SMS) is described. Numerical simulation is performed to multimode fiber with graded-index and step-index using finite difference-beam propagation method (FD-BPM). Features such as self-focusing location and exciting mode are compared to show the advantages of multimode fiber with graded-index. According to self-focusing effect, focusing and diverging functions of multimode fiber with graded-index are analyzed on theory. The shorter fiber is used in lens and the main applications at present are summarized.