倾斜长周期光纤光栅薄膜传感器特性研究

为设计高灵敏光纤光栅薄膜传感器，基于耦合模理论研究了表面镀制高折射率敏感薄膜的倾斜长周期光纤光栅（TLPFG）耦合特性和薄膜折射率传感特性。TLPFG能激发高阶（角向序数l1）包层模耦合，高阶包层模耦合系数随倾角增大而增大，80时，高阶包层模耦合系数远小于1阶包层模耦合系数。研究表明，光栅倾角变化不影响包层模耦合谐振波长，但影响光谱透过率。进一步研究了TLPFG在80时1阶5次包层模耦合的光谱透过率对薄膜折射率变化的响应，分析了光栅结构参数（L、、）和薄膜参数（h3，n3）对薄膜折射率响应灵敏度的影响，结果表明，响应灵敏度相比于非倾斜LPFG可提高一个数量级，对薄膜折射率的分辨率可达10-9。

Characteristics of film sensor based on tilted long-period fiber gratings

In order to design a high-sensitive fiber-grating-based film sensor, the coupling features and sensing characteristics to the film refractive index of tilted long-period fiber gratings (TLPFG) coated with high-refractive-index sensitive films were studied, based on the coupled-mode theory. TLPFGs can couple the core mode to higher-order(azimuthal number l1) cladding modes whose coupling coefficients increased with the tilt angle and were much less than that of the first-order cladding mode for 80. It is confirmed that the tilt angle plays a role in determining the spectral transmittance rather than the resonant wavelength of the cladding-mode coupling. The response of spectral transmittance related to the 1-order and 5-number cladding mode of TLPFG to the variation of film refractive index were investigated under 80. The dependence of sensitivity of coated TLPFGs on the grating structural parameters(L,,) and film optical parameters(h3,n3) were analyzed. Result shows the sensitivity is greater than that of the non-tilted LPFGs by one order and the resolution of film refractive index is available to be 10-9.