中文摘要：

对于涂覆长周期光纤光栅（LPG）传感元件,涂覆层折射率大于包层折射率时将具有很高的灵敏度。然而在涂覆层厚度为纳米量级时,涂覆层的折射率将具有一定的吸收,吸收将对LPG传感元件产生一定的影响。本文在线偏振（LP）模近似理论和耦合模理论（CMT）的理论模型基础上,通过数值计算对这一情况进行研究讨论。详细分析了模式转变点附近和远离模式转变点区域涂覆LPG的模式结构和透射谱情况。在无吸收的理想模型基础上,详细分析了消光系数对模式转变和重新组合的影响,以及模式结构的转变对LPG透射谱的影响,得出吸收将会导致LPG灵敏度、可测量的动态范围的变化。最后,文章给出了一种新型的LPG吸收传感元件的模型。

英文摘要：

As the refractive index of the overlay is higher than that of the cladding, the Long Period fiber Grating （LPG） element exhibits high sensitivity. However, when the thickness of the overlay is tens of nanometers, the material of the overlay present a high absorption, and the absorption can impact the property of the LPG element. A numerical study based on the linearly polarized （LP） modes and the coupled-mode theory （CMT） is used for our research. The analyses mainly comprise the mode structure and the spectrum influenced by the transition intervals which include both the transition nearby and the transition apart. On the basis of the non-absorption ideal mode, we studied the transition and re-organization of the cladding modes caused by the absorption, as well as its impact on the spectrum of the LPG. The result shows that the absorption causes the sensitivity and the dynamic range of the LPG element changed. Finally, we present a new absorption LPG sensor element.