中文摘要：

利用等效介质结构，将圆形光子晶体光纤的二维光子晶体结构近似为一维结构，应用平面波法得到其能带结构．考虑实际Bragg光纤与圆形光子晶体光纤的共同之处，同样将其近似为一维光子晶体，得到能带结构，结果与以前直接的一维平面波法得到的能带结构存在细微差异．

英文摘要：

Utilizing the effective-medium structure, the two-dimensional lattice structure of circular PCF can be approximated to an one-dimensional structure, and the photonic band gaps can be calculated by the plane-wave expansion method. Considering the analogy between Bragg fiber and circular PCF, the band diagram of the Bragg fiber can be also obtained with one-dimensional approximation. There are slight differences between our results and the previous occasion. The complexity of the calculation can be reduced by using the effective medium structure and one dimensional approximation.