全光纤干涉式结构中传感模式仿真分析

全光纤干涉式传感结构中包层模场与外界物理量作用,携带被感测信息,因此对包层模的研究是设计制作和提高该类传感器传感性能的关键.利用有限差分光束传播法获得传感光纤不同长度和不同芯径比时传感器对应的光谱,通过傅里叶变换获得其干涉频谱,计算出各主要参与干涉的包层模组的有效折射率,利用色散方程确定对应包层模.理论仿真结果显示,随着传感部分光纤长度增加,参与干涉的包层模式随之增加,并且向高阶模式变化,光谱变得稠密,是多阶包层模干涉的叠加,传感器输出干涉谱的自由光谱范围变小.随着输入光纤与传感光纤芯径比变化,会明显改变纤芯包层功率分布,同时,芯径比增大也会增加参与干涉的包层模种类和阶数.

Simulation and analysis of sensing modes of in-fiber interferometer

The cladding mode of the in-fiber interference sensor relates to the externally sensing physical quantity, so the investigation of the cladding mode is very important for designing and improving the sensing performance of the sensor. By using the finite difference beam propagation method, the interference spectra of the sensors with different lengths and different core-to-core diameter ratios are simulated. Its spatial frequency spectrum is obtained through Fourier transform. The effective refractive index of the dominant cladding mode can be obtained through analyzing its spatial frequency spectrum. Its corresponding cladding mode order can be determined through substituting the values of the effective refractive index into the dispersion equation of sensing optical fiber. The simulation results show that the number and the order of the cladding modes both increase with sensing part fiber length increasing. The interference spectrum becomes dense according to the superposition of multi order cladding mode interferences. Its free spectral space of the sensor output interference spectrum becomes small. With the variations of the input fiber and sensing fiber core-to-core diameter ratio, the power distributions among the modes change obviously. The increase of core-to-core diameter ratio can increase the number and order of the cladding modes.