中文摘要：

仿真分析了单轴晶体光纤的两层介质模型与三层介质模型所得纤芯模有效折射率的差别，并基于该差别对长周期光纤光栅的外界环境折射率、温度和轴向应变传感灵敏度进行了仿真分析。结果表明，对两层、三层介质模型的纤芯模，尤其对薄包层光纤有效折射率有较大差别；用两层介质模型和／或材料的折变系数计算所得的长周期光纤光栅的外界环境折射率、温度和轴向应变灵敏度有较大的误差，需应用三层介质模型以及模式的有效折变系数进行准确计算。据此计算了上述3种传感灵敏度与光纤包层半径及包层模序数的关系。为长周期光纤光栅传感器的分析设计提供了指导。

英文摘要：

The contrast between the effective refractive indices （RIs） of the core mode in a uniaxial-crystal fiber yielded respectively by two fiber analysis models, namely the two-layered medium model and three-layered medium model, is simulated and analyzed. Based on this, the surrounding RI, temperature and axial strain sensitivities of a long-period fiber grating （LPFG） are calculated. The result shows that the core-mode effective RI difference produced by the two fiber analysis models is significant, especially in the case of thin cladding layer. Moreover, the surrounding RI, temperature and axial strain sensitivities calculated from the two layer model and/or the materials＇ sensing-parameter-induced optical coefficients have significant error, and it is necessary to employ the three layer model and the correspondent model effective RI coefficients to obtain accurate results. The relationship between the sensitivities and the cladding mode order for different clad radii is calculated. This paper provides guidance to the analysis and design of LPFG based sensors.