长周期光纤光栅三层结构折射率梯度响应特性研究

Research on Response Characteristics of the Refractive-index Gradient Based on a Three-layer Long-period Fiber Gratings

基于模式耦合理论和传输矩阵法,使用三层结构圆光波导模型对长周期光纤光栅(LPFG)包层模(HE14)的响应特性进行仿真和分析。通过对比分析外部环境折射率呈梯度分布时与呈均匀分布时的LPFG透射谱,发现谱线中除了损耗峰发生漂移以外,主峰左侧旁瓣深度增加,主峰右侧旁瓣深度减小,且随外部环境折射率的升高,这种变化趋势愈加明显,分析了透射谱发生相应变化的原因。研究结果对使用LPFG进行折射率梯度传感设计具有一定意义。

Based on the mode coupling theory and transfer matrix method,the response characteristic of the long period fiber grating（LPFG） cladding mode（HE14） were simulated and analyzed by using three-layer cylindrical waveguide model.Research results show that,compared the LPFG transmission spectrum under the external refractive index（RI） in gradient distribution with that under the external in uniform distribution,the loss peak of LPFG shifts,and the depth of the sidelobe increases in the left side but decreases in the right side of resonant wavelength.With the increase of external RI,this trend is more obvious.The corresponding changes of transmission spectra are also analyzed in this paper.The research results are meaningful for the RI gradient sensor design based on LPFG.