1 550 nm单模锥形光纤模场的演化特性

根据光纤模式传输理论，结合单模锥形光纤的结构，使用有限差分光束传播法(FD-BPM)仿真了1 550 nm波长下光纤模式的传输，分析包层内模场和纤芯内模场之间的相互影响。仿真结果表明:因为包层模的存在，随着包层内模式数的减少和纤芯对模场约束状态的变化，锥形光纤纤芯内不同区域模场分布变化明显，模场的均方根宽度在不同区域有不同程度的起伏。通过数值计算得到了光纤内模场能量的分布，发现因为包层模的存在，纤芯内模场能量减小速度比没有包层模时的速度要慢。

Mode field evolution in 1550 nm single-mode tapered fiber

According to the theory of optical fiber transmission mode, combined with the structure of single-mode tapered fiber, the paper uses finite difference beam propagation method (FD-BPM) to simulate the transmission of fiber mode at 1 550 nm wavelength, and analyzes the influence of the mode in cladding on the mode in fiber core. The results show that, because of the existence of cladding mode, with the reduction of cladding mode number and the change of the constraint state of mode field in fiber core, the mode field distribution within different regions of tapered fiber core changes significantly, and the root-mean-square(RMS) widths of mode field within different regions have different degrees of ups and downs. The distribution of mode field energy is obtained by using numerical method and the existence of cladding mode is found to slower the reduction of mode field energy.