【作者】 宋世德；

【导师】 于清旭；

【作者基本信息】 大连理工大学 ， 光学工程， 2006， 博士

【摘要】 长周期光纤光栅是一种周期在数百微米的光纤光栅，由于插入损耗低、背向散射小、制作简单以及成本低等优点，在光纤传感和光纤通讯领域有良好的应用前景。本文提出了采用CO₂激光脉冲制作长周期光纤光栅的新制作方法，并对该方法制作的长周期光纤光栅的光谱特性和传感特性进行研究。论文内容主要包括以下几个方面： 1、本文建立了光纤三层模型，从矢量亥姆霍兹方程出发，根据电磁场的边界连续条件，得到了隐式的包层模特征方程，然后采用快速搜索和逐步逼近的方法对包层模的有效折射率进行高分辨率的快速求解。文中同时对长周期光纤光栅的光谱特性进行分析和数值模拟，为长周期光纤光栅的制作和传感研究提供理论参考。 2、本文首次提出了利用三束聚焦的高频CO₂激光脉冲角向对称写入系统制作长周期光纤光栅的方法，具有写入系统结构简单、易于控制、调节等优点，能够制作出插入损耗小，带宽窄的长周期光纤光栅，同时能消除CO₂激光单侧写入方法引起的折射率改变不均匀的问题，保证长周期光纤光栅具有相对一致的弯曲特性，减小了长周期光纤光栅的偏振相关损耗。本方法已获得国家发明专利。 3、本文采用Corning SMF-28光纤，通过对称写入方法制作出纤芯导模与低阶包层模之间产生能量耦合的长周期光纤光栅，并对光栅的温度、轴向应变、弯曲以及环境折射率等特性进行理论分析和实验研究。从长周期光纤光栅和布拉格光纤光栅的高温实验对比可以看出，长周期光纤光栅具有较高的温度灵敏度和高温稳定性，适合于高温环境下的温度传感。对长周期光纤光栅轴向应变的测量结果表明，其轴向应变灵敏度与布拉格光纤光栅的相近或者低一个量级左右，远小于长周期光纤光栅的温度灵敏度。对长周期光纤光栅弯曲特性的测量结果表明，采用单面写入技术制作的长周期光纤光栅存在对应变最为灵敏两个方向和最为不灵敏的两个方向，而采用本文对称写入技术制作的长周期光纤光栅则具有相对一致的弯曲特性。对长周期光纤光栅环境折射率敏感特性的实验结果表明，长周期光纤光栅可以实现折射率／浓度的实时测量，并且灵敏度高，而通过腐蚀包层半径的方法可以进一步环境折射率的敏感性。 4、本文制作了温度可调谐长周期光纤光栅带阻滤波器，基于该滤波器的线性边带提出了布拉格光纤光栅动态应变测量系统。由于温度可调谐长周期光纤光栅带阻滤波器的线性范围宽、动态范围可调，因此能够自动适应布拉格光纤光栅应变传感器所在环境温度的变化，使布拉格光纤光栅传感器的反射波长的初始位置始终位于滤波器线性边带更多还原

【Abstract】 Long period fiber grating(LPFG) is a kind of fiber grating with a period of several microns, which has good prospects in optical fiber sensor and optical fiber communication areas with advantages of low insertion loss, low back-reflection, easy fabrication and low cost. In the thesis, a new LPFG fabrication method based on carbon dioxide laser is proposed, and the optical spectrum characteristics and sensor applications of the LPFG is studied. The main research works includes:1. Based on vector Helmholtz equation and electromagnetic field boundary conditions, the implicit dispersion equation of three-layer cylindrical waveguide can be derived. A repaid scan and step-by-step method are adopted to solve the effective refractive index of cladding modes with high resolution and fast speed. Theoretical analysis and numerical simulation of transmission spectral characteristics is a good reference to the fabrication and sensor application of LPFG.2. A new symmetric fabrication method based on three focused high-frequency carbon dioxide laser beams is promoted for the first time. The system with advantages of simple structure, easy to control and adjustment can eliminate the asymmetric refractive index modulation caused by side exposure method. The LPFG fabricated with the system has low insertion loss and narrow bandwidth, also have relative uniform bending character, low polarization dependence loss. The fabrication method is patent protected now.3. LPFGs which couple guide modes to low order cladding modes are fabricated on telecommunication fibers of SMF-28(Corning) with the method as mentioned above. The characteristics of temperature, axial strain, bending and surrounding refractive index of LPFGs are investigated in the thesis. The LPFGs have high temperature sensitivity and high temperature stability in comparison with fiber Bragg gratings(FBG), which are suitable to be used under high temperature. Compared with FBG, the axial strain sensitivity of LPFG is smaller. The bending measurements show that LPFG fabricated with side exposure exists the most bend-sensitive two orientations and the most bend-insensitive two orientations, but LPFG fabricated with symmetric exposure method shows similar bend characteristics. The refractive index experiment shows that the LPFG can be used to measure refractive index and concentration with fast speed and high resolution. The refractive index sensitivity of LPFG can be further improved by etching the cladding radius.更多还原