光纤陀螺中使用的Y分支相位调制器对单模特性要求非常高。文中深入研究了Y分支波导的多模特性,在理论分析的基础上用BPM做了Y分支的设计和仿真,模式耦合分析表明,当Y分支波导为多模时,其倒置输入时的输出功率会随波长变动发生周期性波动,该特征可用于定量判定多模临界波长。归纳数据,提出了一种独特的通过Y分支输出功率曲线测定其多模临界波长的方案,并且通过Y分支波导的测试实验验证了该方案的有效性。

The phase modulator with Y-branch waveguide which is used in the fiber-optic gyroscope (FOG) has high requirement to be single-mode. With deep study of the multi-mode characteristics, a Y-branch waveguide is designed and simulated with BPM software based on the theoretical analysis. Analysis of the mode coupling shows that the output power of the inverted input Y-branch waveguide is periodical fluctuated with the wavelength, when the waveguide is in multi-mode. And this characteristics can be used to judge the multi-mode threshold wavelength. Proposed a method that multi-mode threshold wavelength can be found out from the figure of the output power which changes with the wavelength. And this method is verified by testing an actual Y-branch waveguide.