【作者】 王莉；

【导师】 李志全；

【作者基本信息】 燕山大学 ， 检测技术与自动化装置， 2003， 硕士

【摘要】 本文在分析国内外长周期光纤光栅的研究现状以及折射率测量存在的问题的基础之上，对长周期光纤光栅理论进行详细的分析研究，建立了长周期光纤光栅的数学模型，并设计了基于级联长周期光纤光栅的折射率测量系统，对系统的可行性及可能存在影响因素进行了分析和实验研究。文中首先从弱导光纤出发，采用简化的三层模型对导模及包层模本征方程进行了推导，并求解出给定参数的光纤导模以及前二十个一阶包层模的传播常数及有效折射率，在此基础上对各次包层模对外界折射率的敏感性进行了研究，选出了最适合于折射率测量的包层模式。其次从耦合模理论出发，建立了长周期光纤光栅的数学模型。 其次根据所建立的长周期光纤光栅的数学模型，对具有不同长度、周期、耦合强度以及折射率增量的长周期光纤光栅透射谱特性进行了研究，并推导了谐振峰半峰带宽与光栅参数之间的关系式。此外，还分析和研究了在不同位置引入不同相位跳变的相移光栅、并联长周期光纤光栅以及级联长周期光纤光栅的光谱特性，选择出适用于折射率测量的合理光栅参数及光栅组合方式。在理论分析研究的基础上，设计了基于级联长周期光纤光栅的、采用相位生成载波技术对被测量信号进行解调的折射率测量系统，并对系统的可行性进行了较为详细的论证。最后对所设计的长周期光纤光栅折射率测量系统进行实验研究。其中包括测量系统主要元器件的工作原理及工作特性的分析，以及实验结果的给出。并对影响测量结果的温度、应变、弯曲等因素进行详细分析研究，发现弯曲是长周期光纤光栅测量过程中的主要影响因素，应当在测量过程中严格避免光纤栅区的弯曲。更多还原

【Abstract】 Based on the analysis of long-period fiber gratings’(LPGs) research state and the problems of refractive index measurement, the theory of LPG was in detail analyzed and studied in this dissertation. Firstly, the mathematical model of LPG was established. Secondly, the refractive index measure system based on LPG was designed. Lastly, the feasibility and the influencing factor probably appeared were analyzed and researched through experiments.The eigen equation of fundamental mode and the cladding mode in weak optical fiber was derived using an accurate three-layer geometry model and solved the propagation constants and effective refractive index of fundamental mode and the first twenty cladding mode. Based on the previous work, the cladding modes’ sensitivity to the surrounding media’s refractive index was studied and the fittest cladding mode for refractive index measure was selected. From coupled mode theory, the mathematical model of LPG was established.LPGs’ transmitted spectrum property with various length, period, coupled intensity and index change were researched in the light of the established mathematical model, and the relation between Full Width Half Maximum (FWHM) and parameter of grating was derived. Besides, the spectrum property of the phase shift LPG with different phase shift in different position and parallel or cascade LPG were also analyzed and studied. The fiber grating’s parameter and combination fit for refractivity measure were selected.On the basis of the theoretical analysis and research, the refractivity measurement system was designed, which was based on cascade LPG and phase generated carrier technique. The feasibility of system was in detail demonstrated.Last, the refractive index measurement system based on LPG designed in this paper was research in the experiments. Including the analysis of the working principle and characteristic of the main devices in the measurement<WP=6>system. At the end of the dissertation, the testing result was given and the influencing factor such as temperature, strain, bend and so on were analyzed too. And it was found that bend is the main influence and it must be strictly avoid during the process of measuring.更多还原