基于熔锥型光纤耦合器在拉锥过程中光纤锥形的渐变特性和光纤之间熔融度的变化特点, 构建了光纤耦合器在拉制过程中波导结构的变化模型.利用光束传播法对耦合器的拉制过程进行数值模拟, 得到耦合器输出光功率随拉伸长度的变化规律以及耦合器的能量分布图.理论模拟和实验结果表明, 光纤间熔融度与制作耦合器时的氢气流量及拉伸速度有关, 氢气流量大, 拉伸速度小, 熔融度就大；光纤之间的耦合作用与拉伸长度及熔融度有关, 拉伸长度增加或熔融度增大, 都会使光纤间的耦合更加显著；拉伸长度不大时, 锥形区的耦合可以忽略；随着拉伸长度的增加, 光纤变细, 耦合作用逐渐增强, 锥形区的耦合现象越明显, 同时光场也逐渐由纤芯向外发散, 产生附加损耗.

Based on the gradient characteristic of taper of optical fiber and the change of degree of fusion between two fibers of fused fiber coupler in the drawing process, the changing model of waveguide structure of optical fiber coupler was constructed. The relationship between optical power and stretching length was obtained, and optical field distribution during drawing process was gotten by numerical simulation with beam propagation method. The simulation and experimental results show that hydrogen flow and drawing speed have an influence on degree of fusion. Large hydrogen flow and low speed make degree of fusion large. The coupling effect between fibers is related to the stretching length and the degree of fusion. Long stretching length and large degree of fusion make coupling effect strong. When the stretched length is short, the coupling of taper region can be ignored. On the one hand, it’s revealed fibers become thinner and coupling effect becomes stronger in taper region with the increasing of stretched length. On the other hand it is also showed that the energy leaks out of the fiber and it leads to excess loss.