为了探究非对称耦合器的特性, 利用具有折射率差异的两根光纤制作了宽带耦合器。采用数值计算模拟了不同折射率差光纤耦合器的光场分布以及输出光功率随拉伸长度的变化曲线, 并分析了两种宽带耦合器的带宽差异以及熔融度对功率转换比的影响; 采用光束传播法, 通过仿真模拟得到了理论带宽。结果表明, 耦合的功率转换比随两根光纤的不对称情况而变化, 功率转换比调节到耦合器分束比的大小时, 耦合器带宽最宽; 熔融度对宽带耦合器分束比有一定的调节作用; 3dB光纤耦合器在C+L波段波长响应平缓, 带宽范围达到150nm; 分束比3∶7和1∶9的耦合器带宽范围分别是210nm和330nm; 分束比1∶99的耦合器带宽范围是420nm。此研究结果对制作非对称宽带耦合器提供了参考依据。

To explore characteristics of asymmetric couplers, a broadband coupler was fabricated by using two optical fibers with different refractive index. The distribution of optical field of fiber couplers with different refractive index differences and the curve of output optical power with stretching length were simulated by numerical calculation. Bandwidth difference between two broadband couplers and the influence of melting degree on power conversion ratio were analyzed. The theoretical bandwidth was obtained by simulation based on the beam propagation method. The results show that, the coupling power conversion ratio varies with the asymmetry of two optical fibers. When the power conversion ratio is adjusted to the splitting ratio of the coupler, the bandwidth of the coupler is the widest. The melting degree can regulate the beam splitting ratio of broadband couplers. The wavelength response of 3dB fiber coupler in C+L band is gentle. The bandwidth range is 150nm. The bandwidth ranges of couplers with beam splitting ratios of 3∶7 and 1∶9 are 210nm and 330nm, respectively. The bandwidth range of the coupler with beam splitting ratio of 1∶99 is 420nm. The results provide a reference for the fabrication of asymmetric broadband couplers.