运用平面波法研究了光波入射二维光子晶体时的模场分布，包括周期性结构、中心引入点缺陷和线缺陷三种情况。结果表明：对于完全周期性光子晶体，其模场是波矢量k 的周期性函数；不同的k 即使对同一个能带也存在不同的模场分布；模场主要分布在高介电常数的区域，且呈现高度对称性；除了简并模，相邻模场正交；模场分布形状与晶格结构有关，正方晶格模场呈现正方形分布；而对于不同的点缺陷，点缺陷半径不同，模场分布不同；当二维光子晶体中存在线缺陷时，其模场分布在缺陷及其周围的区域，呈现明显的周期对称性。

The mode field distributions are studied by using plane wave method. The influence of periodic structure, point defect and line defect on mode field distribution are discussed in detail. The results reveal that the mode field is a plane wave along k-direction modulated by a periodic function, just as indicated by Bloch theorem; the mode field is changed with k even with one band; mode field mainly locates in the areas of high dielectric constant, and shows a high degree of symmetry; mode fields in neighboring bands are orthogonal except those degenerate bands; the mode field shapes are relation with the lattice structure, the square lattice show square shape; the mode field distributions are different for different defect radius. Mode field distribute in the defect and its surrounding area and shows significant period symmetry.