利用光束传输法，分析设计了一种只由两个定向耦合器构成、能直接与单模光纤相耦合、易于集成的平面光波导(Planar Lightwave Circuit,PLC)型1.31/1.49/1.55 μm单纤三向器.该器件的输入输出弯曲波导和耦合区平行波导均采用光束传输法进行优化设计，并对器件的折射率进行了容差分析，获得了当两个定向耦合器的耦合长度分别为6 578 μm、3953 μm时，器件对各波长的隔离度均在47 dB以上，且插入损耗小于0.05 dB.

A 1.31 μm /1.49 μm /1.55 μm planar-lightwave-circuit (PLC) triplexer consisted of only two directional couplers was proposed and designed based on the beam propagation method.It is ease of both the connection with optical fibers and hybrid-integration with active component.The input and output bended waveguides and the paralled waveguides of the triplexer were all optimized by the beam propagation method (BPM),and its index toleration was also analyzed.The optimized lengths of the two directional couplers are 6 578 μm and 3 953 μm,respectively,with the wavelength isolation of the device above 47 dB and the insertion loss is less than 0.05 dB for all wavelengths.