利用全矢量耦合模方程提出并分析了一种基于纤芯存在光致双折射的长周期光纤光栅的环境折射率传感测量方法.以波长为谐振波长的完全偏振光为入射波, 通过分析不同环境折射率下输出光的偏振态在邦加球上与参考点间球面距离的变化测量环境折射率.分析表明,在环境折射率1～1.30范围内包层半径为20.75 μm的长周期光纤光栅传感器线性特性良好, 灵敏度为0.356/RIU, 可应用于湿度和气体的折射率测量;该分析方法适用于其他类型的双折射长周期光纤光栅传感器的设计.

Using the full-vector coupled mode theory, a method for Surrounding Refractive Index (SRI) sensing with a single wavelength was proposed which is based on the core-only photoinduced birefringence of Long-Period Fiber Grating (LPFG). With a completely-polarized light near the resonant wavelength launched into the LPFG, the variation of the spherical distances between the output light polarization states for various SRIs and that for the reference SRI=1 on the Poincare sphere is investigated to identify the SRIs. The analysis indicates that the SRI sensor with a cladding radius of 20.75 μm shows a good linearity performance and high sensitivity of 0.356/RIU over the SRI measurement ranging from 1 to 1.30, which, unlike the available LPFG sensors, may be applied to the humidity and vapor sensing. Meanwhile, the analysis method is applicable to the design of other types of birefringent-LPFG sensors.