【作者】 刘迪仁；

【导师】 章献民； 陈抗生；

【作者基本信息】 浙江大学 ， 电子科学与技术， 2005， 博士

【摘要】 布里渊分布式光纤传感器技术因其自身的优点和广阔的应用前景而成为目前国内外传感器研究的热点课题。本文在全面调研相关文献基础上,理论分析和数值模拟相结合,分析了脉冲光在25km光纤中的布里渊散射特性,建立了布里渊散射谱与光纤温度、应变和应变梯度等的调制解调关系,对布里渊分布式光纤传感器(B-DOFS)的测量原理、系统设计以及应变、应变梯度、温度等的长距离分布式模拟实验测量等方面作了较系统的研究。并在应变梯度对B-DOFS测量精度的影响、改善BOTDR系统性能的消偏振衰落技术等方面做了较深入的研究。本文的研究来源于国家863项目子课题“长距离海底管道分布式光纤传感技术”(G20020477),课题已通过863专家组验收,并评价为整体国内先进,部分国际领先水平。本文的主要贡献可归纳为: (1)采用了有效的数值分析模型和方法分析不同宽度的脉冲光注入普通单模光纤布里渊散射功率谱变化和阈值特性。对采用脉冲泵浦的布里渊分布式光纤传感器,其结果为系统设计中的参数优化提供了理论参考。 (2)为减小偏振失配对布里渊谱测量精度的影响,针对B-DOFS系统信号特点,首次提出了光时域分集消偏振技术(TDPD),并给出了较详细的理论分析和论证。不管布里渊散射信号光的偏振态如何随机变化,采用该技术可使接收信号对偏振态随机变化不敏感。将TDPD应用于B-DOFS系统中,对比采用该技术前后的实验统计结果表明,采用该技术后的接收信号功率幅度起伏要比采用前的小约4.2倍,实验验证了其改善系统性能的有效性。 (3)在建立布里渊谱参数与应变和温度的调制关系基础上,首次提出了采用加权最小二乘优化反演方法从布里渊散射谱同时解调温度和应变的分布,并给出了有特色的权系数确定方法。 (4)采用B-DOFS系统对25km传感光纤作了全分布式的应变、温度模拟实验测量,该实验系统目前空间分辨率可达7.5m、应变和温度的分辨率分别可达50με和3℃。另外,系统空间分辨率范围内应变梯度对布里渊谱测量影响的理论分析和数值计算结果表明,应变梯度增大不仅使布里渊频移随之线性增大,也会使后向布里渊散射谱峰值非线性降低,谱峰变得平坦。空间分辨率10m的100με/m应变梯度相对于零应变梯度,引起的布里渊频移测量误差增加2.04倍。并对大型梁结构应变梯度的影响作了模拟实验研究。更多还原

【Abstract】 A lot of interest has been focused on Brillouin distributed optical fiber sensor (B-DOFS) for the recent several years because of its many advantages and potential applications. In this thesis, based on a review of the distributed optic fiber sensors, the characterization of Brillouin scattering in the 25km single-mode fiber pumped by the pulses with the different width is investigated by theoretical analysis and numerical simulation;The relationships of modulation and demodulation between Brillouin spectrum and stress and temperature of the sensing fiber are founded;The measurement principles, equipment configurations, and experimental tests of the distributed stress and temperature along the 25km sensing fiber have been studied. In addition, the effect of the stress gradient on the accuracy of Brillouin spectrum, and the polarization-induced fading elimination technique for improving the performance of B-DOFS have been studied in detail. The main contributions of this dissertation can be briefly summarized as follows:(1) The Brillouin spectrum and its threshold power of the 25km sensing fiber pumped with the different width pulse are analyzed by the effective numerical simulation model and method. It provides the theoretical basis for the parameter optimization of equipment design.(2) In order to reduce the effect of polarization mismatch in the coherent detection system for B-DOFS, based on the feature of Brillouin scattering light and the principles of the polarization spreading and the polarization diversity, the time domain polarization diversity (TDPD) technique is introduced for the first time. The theoretical analysis shows that more than half of signal power is heterodyned with the local light no matter how their polarizations vary, and the received signals are insensitive to the random variation of the polarization of Brillouin backscattering light. The experimental comparison between the system with and without TDPD shows that the fluctuation of the received signal light power with TDPD is 4.2 times less than that without TDPD.(3) Based on the modulation relationship between Brillouin scattering spectrum and stress and temperature, It is presented that simultaneous temperature and stress along the sensing fiber are demodulated from Brillouin spectrum by the weighted least square method, and our special method todetermine the weighted number.(4) The experimental tests of the distributed stress, stress gradient and temperature along 25km fiber by B-DOFS are investigated. The experimental results demonstrate that the stress and temperature vary linearly with Brillouin frequency shift. Its spatial resolution and resolution of stress and temperature separately are 10m,100u.e,and 5°C. In addition, The analytic relationship between Brillouin backscattering spectrum and stress gradient is set up to investigate the influence of the stress gradient within the resolution on the measurement accuracy of Brillouin frequency shift. The numerical results show that the increasing stress gradient results in the linear increasing of the Brillouin frequency shift, the nonlinear decreasing of the peak and the flatting of Brillouin spectrum. With the spatial resolution of 10m and the stress gradient of lOOue/m, the measurement error of Brillouin frequency shift is 2.04 times larger than that without the stress gradient. The Brillouin spectra and stress along the test fiber are experimentally measured at different stress gradients with the sensing fiber fixed on a cantilever beam. Experimental results are in agreement with the theoretical prediction.更多还原