研究结构化光纤Bragg光栅（FBG）在折射率（RI）呈线性分布的液相介质环境下的响应特性。数值仿真结果表明，结构化FBG的反射谱特性强烈依赖于液相介质折射率（RI）的线性分布函数的某些特征参数，比如液相介质的RI沿FBG轴向的分布梯度、RI在FBG两端的差值等。基于理论仿真结果，建立了结构化FBG在低RI区（1.330~1.360）对液相介质的RI梯度进行测量的线性近似理论模型。通过相关实验研究，证明了理论仿真和分析的合理性及基于结构化FBG的RI梯度传感器在现实应用中的可行性。

The responsive characteristics of the structured fiber Bragg grating (FBG) under liquid medium with the refractive-index (RI) linear distribution are analyzed. The simulated results show that the reflection spectrum of the structured FBG are closely related to the properties of the RI distribution function of the liquid medium, such as the RI gradient along its axis and the value of the RI at both of its ends. Based on the numerical results, the theoretical model for the linear-approximation measurement of the RI gradient of the liquid medium by the structured FBG at the low RI area (1.330~1.360) is established. Through the experiments, the feasibility of the theoretical simulations and analyses and the practical applications of the RI gradient sensor based on the structured FBG are verified.