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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 model coupling theory and transfer matrix method, the response characteristics of long period fiber grating (LPFG) cladding mode (HE14) were simulated and analyzed using a three-layer circular waveguide model. By comparing the transmission spectra of LPFG with gradient distribution and uniform distribution, we found that in addition to the shift of the loss peak, the depth of the left side lobe of the main peak increases and the depth of the right side lobe of the main peak decreases With the increase of the refractive index of the external environment, the change tendency becomes more obvious. The reason of the corresponding change of the transmission spectrum is analyzed. The results of this study have some significance for the design of refractive index gradient sensing using LPFG.