将两个二维空气孔光子晶体波导平行放置，两波导之间由三排空气孔相隔，构成一个定向耦合器.数值分析了TE(磁场平行于空气孔)和TM(电场平行于空气孔)偏振态光波在该定向耦合器中的传播行为.结果表明，减小耦合区两波导间的一排介质柱的半径，TE模的耦合长度减小，而TM模的耦合长度不变.基于此结构，设计了超微偏振光分束器，整个器件的尺寸为10.1 μm，与已报道的24.2 μm的结果相比，该器件具有更小的器件尺寸和更高的输出效率.

Two photonic crystal waveguides with triangular lattice of air holes together,between which there are three rows of air holes,are put in parallel to construct a directional coupler.The propagation of TE(electric field parallel to the axis of the air holes) and TM(magnetic field parallel to the axis of the air holes) polarizing lights in the proposed directional coupler is analyzed numerically.The results show that the coupling length of TE light is reduced whereas the coupling length of TM light do not change when the radius of one row of the dielectric rods between the two waveguide of the coupler are modified.On the basis of this structure,ultracompact polarizing beam splitter is designed and the length of the device is only 10.1 μm.Compared with the previous results of 24.2 μm,this device is smaller and more efficient.