分析了光纤制造中产生折射率中心凹陷的原因，建立了折射率中心凹陷GIF (渐变折射率光纤)模型，应用射线光学方法得出了光纤传输的时间延迟、自聚焦周期的表达式，数值模拟了中心凹陷GIF的自聚焦周期和时间延迟。仿真结果表明: 随着凹陷宽度和凹陷深度的增大，GIF中光束的自聚焦效应变差，时间延迟差增大。

This paper analyzes the causes of the generation of a central dip in the refractive index in fiber fabrication, sets up a model of the Graded-Index Fiber (GIF) with such a central dip and obtains the expressions for the time delay and self-focusing period of light transmissions by using the ray optics method. Simulation results show that with the increase of the dip width and depth, the self-focusing effects of the light beams in GIF become worse and the time delay difference increases.