中文摘要：

用薄膜光学的等效导纳方法和阶跃光纤的几何光学理论研究布拉格光纤的传输特性。①设计出了反射率达99．99％包层的厚度、层数；②分析了传输效果随波长、层数、入射角的变化；③得出光束的数值孔径小于0．15时，反射率大于99．99％。这一研究对布拉格光子晶体光纤的实际加工及与阶跃光纤耦合具有重要理论意义。

英文摘要：

With equivalent conductance method, the geometry optics theory of step fiber,the light propagation characteristics of Bragg fiber structures have been researched in this paper. First, the thickness and layer number, the reflectivity of which reaches 99.99%, have been designed;Second, the propagation effect which follows the change of wavelength,layer number and the angle of incidence have been analyzed. Third, it have been concluded when the NA of beam of light is less than 0.15 （ the incident angle is 81.37°） ,the reflectivity reaches 99.99%. This research possesses an important meaning for the manufacture of Bragg fiber and the coupling of step fibre.