基于光波导理论与光纤布拉格光栅(FBG)的模式耦合理论,对倏逝波FBG传感器的能量衰减特性进行了分析研究。最后得到了FBG的归一化反射率的表达式,它是外部介质折射率(SRI)和FBG纤芯直径的函数。理论仿真显示FBG归一化反射率会随着SRI增大和FBG腐蚀程度的加深而减小,呈非线性关系。实验结果也证明增大SRI(小于包层介质折射率)或者增大FBG的腐蚀程度都会使光纤纤芯中的传输能量减小,增强倏逝波与外部媒介的相互作用,从而增加传感器的灵敏度。 Based on the theory of mode coupling between optical waveguide theory and fiber Bragg grating (FBG), the energy attenuation characteristics of evanescent FBG sensor are analyzed. Finally, the expression of the normalized reflectance of the FBG is obtained as a function of the refractive index of the external medium (SRI) and the diameter of the FBG core. The theoretical simulation shows that the normalized FBG reflectivity decreases with the increase of SRI and the corrosion of FBG, showing a nonlinear relationship. The experimental results also show that increasing the SRI (less than the refractive index of the cladding medium) or increasing the corrosion of the FBG both decrease the transmission energy in the fiber core and enhance the interaction between the evanescent wave and the external medium, thereby increasing the sensitivity of the sensor .