采用Matlab和Comsol建立单模光纤内激光传输模型，对双包层内光纤折射率和纤芯结构对光能量分布的影响进行了理论研究。系统分析了光纤芯径与数值孔径、归一化频率和功率填充因子的关系，依据得到的结果进一步采用多模物理耦合仿真方法对不同类型的单模双包层光纤纤芯的能量分布进行仿真，探索了不同折射率分布情况对纤芯能量分布的影响。计算和仿真结果表明：凹面折射率分布光纤的光斑模场面积最大，单位面积的功率分布最低。针对大功率光纤激光器的应用需求设计了工作波长为1.064 μm、纤芯直径为10 μm、凹面直径为8 μm、数值孔径为0.12的单模凹面折射率双包层光纤，为提高光纤泵浦效率、降低纤芯的能量密度提供了思路。

The effects of refractive index and fiber core structure on energy distribution were studied by setting up laser transmission model in single mode fiber with Comsol and Matlab. First, the relationship between the fiber core, numerical aperture, normalized frequency and power fill factor was analyzed. Second, the energy density distribution of various designs for the core refractive index of single mode fiber was numerically simulated and compared. According to the calculation and the simulation results, it is concluded that central-dip fiber can enlarge mode area and lower the power density. Finally, due to the application requirement of high power fiber laser, the single mode central-dip fiber was designed with the wavelength of 1.064 μm, the core diameter of 10 μm, the concave diameter of 8 μm, and the numerical aperture of 0.12, which provides an idea for the development of pump efficiency and the reduction of the energy density in fiber core.