【作者】 苗飞；

【导师】 贾磊； 隋青美；

【作者基本信息】 山东大学 ， 检测技术与自动化装置， 2012， 博士

【摘要】 随着光纤及光子器件制造技术的不断完善,光纤光栅已成为目前最具有代表性和最具有发展前途的光纤无源器件之一,广泛应用于光通信和光传感等领域。长周期光纤光栅(long-period fiber gratings:LPFG)作为一种新型的光纤光栅,由于其插入损耗小、带宽宽、后向反射低、对外界环境变化的反应灵敏度高、制作简单、成本低廉等优点,受到国内外广大学者的关注。发展短短数年,已经显示出了极为广阔的应用前景。由于LPFG的周期相对较长,满足相位匹配条件的是同向传输的纤芯基模和包层模,这一特点决定了LPFG的谐振波长和峰值对外界环境变化非常敏感,具有比布拉格光栅(FBG)更好的温度、应变、弯曲、扭曲、横向负载、浓度和折射率灵敏度。因此,LPFG在传感领域具有比布拉格光栅和其他传感器件更多的优点和更加广泛的应用。另外,由于对光纤光栅功能需求标准的不断提高,新结构、新特性、多功能光纤光栅的研制已经成为开发新型光子器件的必然发展趋势。本文在前期对长周期光纤光栅理论以及长周期光纤光栅各种制备方法比较分析的基础上,深入分析了长周期光纤光栅的耦合模原理和各种光栅制备方法的优缺点,设计了基于800nm飞秒激光器的使用逐点刻写法的长周期光纤光栅制备系统,实现了光纤位置的精确控制并利用两个CCD和监视器实现了光纤纤芯与激光脉冲实现了精确对准,并且刻写得到了不同参数谐振峰谱形的长周期光纤光栅。然后又对刻写得到的LPFG进行了包括高／低温、轴向应变、弯曲以及折射率等各种传感特性分析与实验,得到了相应的变化曲线。接着,使用氢氟酸腐蚀以及PSS和PDDA两种聚合物对刻写得到的LPFG进行静电自组装涂覆,用于增强光栅的折射率响应灵敏度,并对增敏后的LPFG进行了折射率灵敏度响应测试。最后,设计了基于LPFG和高双折射光纤Sagnac环镜干涉仪的多参数测量方法。本文的主要内容包括：1.根据三层光纤模型,分析了光纤波导中的模式分布,并合理简化,分析了长周期光纤光栅中的纤芯基模与一阶低次包层模式的耦合,用耦合常数描述了模式耦合的强弱。同时,对长周期光纤光栅的光谱特性进行分析和数值模拟,探索了长周期光纤光栅各参数对其谱形变化的影响,为LPFG的制备和传感应用研究提供理论参考。2.比较分析了光纤光栅制备技术中常见的写制方法,主要介绍了干涉仪法、相位掩板法、逐点刻写法等方法,并分析比较各方法的优缺点。接着介绍目前常见的各类激光器以及实验系统中涉及的800nm飞秒激光器。然后详细分析说明论文采用的基于逐点刻写法和800nm飞秒激光器的长周期光纤光栅刻写系统的各主要组成部分及其功能。并通过实验获得使用光栅制备系统实现光纤位置的精确控制的方法和使用两个CCD和监视器实现光纤纤芯与激光脉冲焦点的精确对准的方法。最后,使用设计的长周期光纤光栅制备系统在未载氢的裸光纤的上成功刻写得到多种不同谐振峰谱形特征的LPFG,刻写得到的LPFG光路损耗低,其谐振峰变化平滑,线宽较窄。通过对刻写的过程进行监测,得到了LPFG写制过程中透射谱线变化趋势,验证了该刻写系统可以准确稳定地保证光纤纤芯与激光脉冲焦点的对准。3.在全面深入研究长周期光纤光栅传感特性基本理论的基础上,对飞秒刻写LPFG进行温度、轴向应变和弯曲特性分析与实验。实验得到,LPFG谐振峰值在30-250℃以及300-800℃两个范围内的随温度升高向长波方向呈线性变化,在两段温度范围内,温度响应曲线的线性度均保持在0.99以上,其温度特性稳定平滑,高温稳定性比较理想。飞秒刻写LPFG谐振峰值在0～800με范围内的随拉力的增加向长波方向呈线性变化,两个谐振峰值对轴向应变的响应灵敏度分别为0.472×10-3nm/με和0.501×10-3nm/,με,线性度均不低于0.993。飞秒刻写LPFG谐振峰随着曲率半径的减小损耗(曲率增加)逐渐减小,并且随着曲率半径的减小谐振峰向短波方向发生缓慢的漂移,但是光栅谐振峰损耗与峰值变化的趋势因弯曲方向的不同而会出现较大的差异。4.实验对飞秒刻写LPFG进行了折射率传感特性分析,并使用浓度10～60%的蔗糖溶液和一系列有机试剂对其进行折射率响应灵敏度实验。实验得到,当外界环境折射率接近光纤包层折射率时,LPFG折射率灵敏度响应越灵敏的结论。然后使用氢氟酸对LPFG进行腐蚀,并使用PDDA与PSS两种聚合物对腐蚀后的LPFG进行静电自组装涂膜,对飞秒刻写LPFG进行折射率增敏实验。涂膜实验后对并增敏后的LPFG进行折射率响应灵敏度测试。实验得到,增敏后的LPFG的折射率灵敏度得到了提高,而且折射率的灵敏度增加了三倍左右,结果表明经过增敏后LPFG可测量溶液的范围和精度都随之增大。5.在对Sagnac效应以及高双折射率光纤Sagnac环镜干涉仪进行理论分析的基础上,设计了使用LPFG和高双折射率光纤Sagnac环镜干涉仪的多参数同时测量系统,并将该系统进行了温度与应变的同时变化,进行了相关测量与验证实验。经过实验得到,该系统的温度分辨率为0.03℃,应变分辨率为1.7με,温度和应变的测量精度为分别可以达到±0.26℃和±17.4με。与其它方法相比,该系统在保持较高的测量精度的基础上保持了光路损耗小的优势。更多还原

【Abstract】 With the optical fiber and photon devices fabrication technology improving continually, fiber grating has become one of the most representative and promising fiber-optic passive components. And it has been widely used in optical communication, optical sensing and other fields.The long-period fiber grating (LPFG) as a new kind of fiber grating has been studied by many researchers all around the world recently, and has got great progresses in a few years. It attracts wildly attention of home and abroad scholars for its advantages such as low insert-loss, broad-band, low back-reflection, sensitive to the changes of environments, low-cost and easy to be fabricated. In addition, designing the new structure, new features, and multi-function photonic devices has become an inevitable trend as the requirements of the fiber Bragg grating functional standard improves. It has shown a very broad application prospects within recent years development.In this dissertation, based on the LPFG inscription technology, coupled-mode theroy and different fiber grating write systems were analysised, an LPFG write system using an800nm laser and point-by-point technology was designed. Using this inscribe system, we inscribed many different LPFGs with different paraments. And, some sensing characteristics, including temperature, axial strain, bending and refractive index characteristics, were analysis and experiments were performed. Then, using chemical corrosion and electrostatic self-assembly method, the long period fiber grating refractive index sensitizing experimental study. Finally, the design of the LPFG and high-birefringence fiber Sagnac interferometer based multi-parameter measurement method was proposed.The main contents of this article include:1. According to three-layer cylindrical fiber model, the fiber mode distribution is analyzed. And the coupling of fiber core-mode and low first-order cladding mode is also further studied. Then using coupling constant describes the strength of mode coupling. Theoretical analysis and numerical simulation of transmission spectral characteristics is a good reference to the fabrication and sensor application of LPFG.2. Main fiber-gratings-inscribe methods were introduced and compared, including interfermeter method, phase mask plate method and point-by-point method, and so on. And the common types of lasers and an800nm femtosecond laser system was introduced in detail. Then a long period fiber gratings inscribed system based on point-by point technology using the800nm femtosecond laser was designed. The functions of the major components were introduced. Using this system, the fiber position could be precisely controlled, and laser pulses could focus precisely on the fiber core using two CCDs and two monitors. Then, many different characteristics LPFGs with different resonance peaks were inscribed in non-hydrogen-load bare fiber. The LPFG is with low road loss and the resonant peak changes in smooth, line width narrow. According to the experiment of monitoring the process of inscription, trend of the resonance peak transmission line is clear, and this system is verified that the alignment of the laser pulse focus is accurate and stable.3. Based of deap study of long period fiber grating sensing characteristics theory, high/low temperature experiments, axial strain experiment and bending experiment was perfomed on the LPFG inscribed with femtosecond laser. It was result from the experiments that in the two temperature range30～250℃and300～800℃, the linearity of the temperature response curve were maintained above0.99, the temperature characteristics is stable and smooth. The resonance peak of the LPFG changes linearly to longer wavelengths at range of0～800με with pull, and the response sensitivity of two resonant peak axial strain were0.472×10-3nm/με and0.501×10-3nm/με, respectively. And the linearity is no less than0.993. The resonance peak of the LPFG decreases with the decrease of the radius of curvature (curvature increases), and the resonance peak drifts to the shortwave direction. But the resonance peak loss peak trends will appear different due to the different direction of bending.4. The refractive index characterstics of LPFG was analyzed, and refractive index sensitivity experiments were performed using concentration of10to60%sucrose solution and a series of organic reagents. It is result from the experiments that the refractive index sensitivity of the LPFG, responses to the more sensitive when the refractive index of the external environment close to the fiber cladding refractive index. Then, refractive index increased sensitivity experiments were performed using of hydrofluoric acid LPFG corrosion and electrostatic self-assembly film of two polymers(PDDA and PSS) on the corrosion of the LPFG. Refractive index characteristics experiment of the sensitized LPFG was performed. It was result that the refractive index sensitivity of LPFG has been improved after sensitizing, and the refractive index of the sensitivity increased about three times. The result showed that after sensitizing, the LPFG measurable range and accuracy of the solution are both increased.5. Based on analysis of high-birefringence fiber Sagnac interferometer, a simultaneous measurement system using LPFG and high birefringence fiber Sagnac interferometer was proposed and experiments were executed with the simultaneous changes of temperature and strain measurement. The result showed that in the system, the system temperature resolution of0.03℃, the strain resolution of1.7με, and temperature and strain measurement accuracy can reach±0.26℃and±17.4με, respectively. Compared with other methods, this system maintains a higher measurement accuracy, and has lower the optical path.更多还原