将相互耦合的3平行光子晶体单模波导看成一个多模干涉系统，通过研究二维正方晶格光子晶体波导多模干涉的自映像效应，优化设计了一种新型1×2光子晶体波导定向耦合分束器，采用时域有限差分法对其传输特性进行模拟分析。设计过程中，根据多模干涉耦合区中周期出现的双重像的位置确定两个单模输出波导的位置，通过改变输出波导和耦合区连结的一个介质柱位置构成波导微腔结构，改变耦合区中的模场分布，实现模式匹配，从而明显减小分束器的反射损耗。计算结果表明，移动介质柱距离输出单模波导和多模波导连结处1.85a位置处时，对于波长为1.55 μm的入射光，该分束器的透射率可高达99.04%。

In the design process of a novel photonic crystal 1×2 power splitter, the coupling of three parallel photonic crystal waveguides can be considered as a multimode interference system in the two-dimensional square photonic crystal. The positions of output waveguides are decided by the positions of periodic twofold image which are formed by the self-imaging effect of multimode interference.The transmission characteristics of the splitter are investigated by using the finite-difference time-domain method. The reflective losses obviously decrease by shifting a dielectric rod in the junction between the multimode waveguide and single-mode output waveguide, and microcavity is constitued, which varies and matches the mode field of the coupling zone. The results show that the transmittance of this splitter can be as high as 99.04% for λ=1.55 μm when the shifted dielectric rod is in the position of 1.85a from the junction between the multimode waveguide and single-mode output waveguide.