基于自发布里渊散射的分布式光纤传感技术及其应用
文献类型：学位论文
| 作者 | 郝蕴琦 |
| 学位类别 | 博士 |
| 答辩日期 | 2013 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 蔡海文 |
| 关键词 | BOTDR 宽带移频 数字相干检测 激光器线宽 脉冲调制格式 线性脉冲编码技术 工程应用示范 |
| 其他题名 | Research on distributed fiber sensing technique based on spontaneous Brillouin scattering and its applications |
| 中文摘要 | 基于光纤中布里渊散射效应的全分布式光纤传感系统利用光纤中布里渊散射谱的频移和强度与外界温度和应变之间的线性函数关系，可以实现光纤沿路温度和应变全分布式高空间分辨率传感，在电力系统、石油管道、大型建筑物健康监测等领域有着广泛的应用前景，是近二十年来光纤传感领域的研究热点。和布里渊光时域分析仪（BOTDA）相比，基于自发布里渊散射的分布式光纤传感技术（BOTDR）具有单端入射、同时对温度和应变敏感等优点，得到了研究人员的重点关注。本文针对BOTDR分布式光纤传感技术中自发布里渊散射信号微弱、具有宽带布里渊频移（约11GHz）、信噪比低、难以实现温度和应变同时解调等诸多核心的关键技术问题，开展了宽带光学移频单元设计、微弱信号的数字相干检测、传感脉冲格式的调制、脉冲编码技术等理论和实验技术研究，构建和集成了整个传感系统，获得了系统的原型样机，验证了系统的性能，并在电力系统获得很好的工程示范性应用。 本论文主要研究内容如下： ■提出一种基于宽带光学移频方案和数字相干检测技术相结合的新型BOTDR分布式光纤传感系统方案，实现了大于30Km光纤传感链路微弱自发布里渊散射信号温度、应变和位置信息多参量全分布式空间高分辨率传感，研制出BOTDR传感系统样机。 设计了基于紧致结构布里渊激光器的宽带移频单元（下频移约10.8GHz）。研究了该移频激光器不同工作状态（自激振荡、单纵模运转）对BOTDR分布式光纤传感技术的影响。实验结果表明，通过与传感布里渊散射信号的相干探测，可实现探测信号带宽由11GHz降至百MHz，降低系统在电子学上对元器件带宽的要求。在信号处理方面，利用数字相干检测技术，通过时域散射信号的数字化信息，进行了传感光纤频移和强度分布的提取，实现了温度和应变的同时传感。此外，论文深入研究了激光器线宽对传感光纤中自发布里渊散射谱的影响，为系统光源优化设计提供指导。 ■从理论和实验上系统研究了不同的脉冲调制格式（类矩形、三角形、洛仑兹、高斯和超高斯等脉冲格式）对BOTDR分布式光纤传感技术中信噪比的影响。仿真研究结果表明：相同脉冲宽度和不同脉冲调制格式时，上升/下降沿时间越长，布里渊散射谱的峰值功率越大。在实验中，通过构建不同传感脉冲调制格式，发现三角形脉冲比矩形脉冲的信噪比高4dB，实现2.5倍的传感长度，和理论分析结果很好的一致。此外，本论文还数值分析了相邻脉冲之间的重叠部分对空间分辨率的影响，研究结果显示这些因素对传感参量的空间分辨性能影响较小。 ■为了进一步改善BOTDR系统的信噪比，初步研究了线性编码技术在BOTDR分布式光纤传感系统中的应用。在理论上，仿真计算了Simplex脉冲编码技术对自发布里渊散射信号信噪比的提高效果，并提出将双正交脉冲编码技术应用于BOTDR系统中，数值分析了其信噪比增加效果；在实验上，展示了Simplex脉冲编码技术在BOTDR传感系统中的应用，并深入研究了编码信号的数字解调方案。实验结果表明，31位编码技术具有3.5dB的信噪比增益，该结论初步验证了线性脉冲编码技术在BOTDR传感系统中应用的可行性。 ■在系统性能检测上，我们将BOTDR原型样机应用于电力线的温度和应变监测等示范性工程上，其包括：1、在覆冰室内对光纤复合地线（OPGW）电缆温度监测，在+/-30℃的测量范围内，其温度准确性<2℃；2、在对三相电缆进行在线温度监测上，通过和分布式拉曼温度传感器（DTS）及热电偶测试系统比较，其测试的结果也具有很好的一致性；3、在传感光缆的应变测量上，实现了6500με传感范围内的准确测量。这些工程示范表明BOTDR分布式光纤传感技术具有温度和应变测量等实际应用的潜力的同时，也为系统地实用化和产品化的进程提供了理论支持和技术支撑。 |
| 英文摘要 | The Brillouin scattering based fully-distributed optical fiber sensor utilizes the two parameters of Brillouin scattering spectrum, the frequency shift and intensity, which are linear to the temperature change and strain variation, so it could detect the temperature and strain signals along the full sensing fiber with high spatial resolution, with application prospect in the domain of the power transmission line, petroleum pipiline, structur health minotoring and so on. Compared with Brillouin time domain analyzer (BOTDA), the Brillouin optical time domain reflectometry (BOTDR) is of obvious advantage, for that it access to single fiber end, sensitive to both temperature and strain change, etc., receiving focused attention from the researchers in the world. With regard to the key technical issues in the BOTDR sensing system, including the weak Brillouin intensity, the wide-bandwidth frequency shift, lower signal-to-noise (SNR), difficult to distinguish the temperature and strain, etc., in this paper we made numerical and experimental research on the design of frequency-shift unit, digital coherent detection of the spontaneous Brillouin scattering, the pulse modulated formats, pulse coding technique. The prototype has been constructed through assembling the whole sensing system. The performance of BOTDR system has been vertificated and it has been successfully applied into the power transmission line monitoring. The main contents in this paper are as followed: ■A new BOTDR dsitributed fiber sensing system is proposed combined wide-bandwidth frequency shifter with digital coherent detection scheme, realizing the fully-distributed BOTDR prototype with the sensing range longer than 30Km, multiparameters sensing (temperature, strain, location). The compact Brillouin fiber laser serves as the wide-bandwidth frequency shifter is designed, whose frequency shift is about 10.8GHz downshifted. The influence of Brillouin fiber laser working on different status (self-lasing oscillating and single longitudinal modes) has been analyzed in detail. The experimental results show that the detected signal bandwidth is reduced from 11GHz to several hundreds Mega Hz, consequently decreasing the bandwidth requirement of the following electronic components. In the signal processing, the digital coherent detection scheme is adopted. The frequency shift and intensity of the Brillouin scattering in the whole sensing fiber are extracted through digitalizing the beat signal in the time domain, finally the sensing of temperature and strain is accomplished. In addition, the linewith of the primary optical source is studied for the BOTDR system, which is important for choosing the proper laser. ■The effects of different pulse modulated formats (rectangular, triangular, Lorentzian, Gaussian, super-Gaussian, etc.) on the BOTDR sensing technique are studied with numerical simulation and experimental analysis. The simulation show that with different rising/fall time for the rectangular pulse, the Brillouin scattering sprectrum has bigger intensity when the pulse develops into trapezoid, and triangular. The experimental results show that the SNR of triangular is 4dB larger than the rectangular, and the sensing distance is more than 2.5 times longer for the latter. Moreover, effects of the overlapped section on the spatial resolution is analyzed, where the influence could be ignored. ■To further enhancement of the SNR in the BOTDR sensing system, the linear pulse code scheme is applied into BOTDR sensing system. In theory, the simulation of Simplex pulse code technique is made, and resluts show that it could improve the SNR of the Brillouin scattering without degrating the spatial resolution; then the Biorthogonal pulse code technique is proposed for the BOTDR system, and the mumeirical simulation is also made. Experimentally the Simplex pulse code is applied in the BOTDR sensing system, and the corresponding digital decoded scheme is researched in detail. The 31 bit coded pulse has 3.5dB SNR improvement in the experiment. All the results proves the effects of linear code technique in the BOTDR sensing system. ■To vertificate the performance of BOTDR prototype, the temperature and strain monitoring for the power tranmission line are made. Some engineering applications are conducted: 1, The optical fiber composite overhead ground wire (OPGW) temperature measurement is carried out in the icing room, the error is less than 2℃ in the temperature range +/-30℃; 2, the on-line temperature monitoring for the three-phase cable is made, the temperature change trend is accordant with other equipments, distributed temperature sensor (DTS) and thermopair; 3, BOTDR sening system has quantitatively measured the strain distribution along the tensile fiber, and the results is accordant to the strian mesaurement instrument. All the above engineering experiments indicate that the BOTDR distributed sensing system is of potential applications, while they also provide the therotical and technical supprot for the system practical and commerical process. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15731]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 郝蕴琦. 基于自发布里渊散射的分布式光纤传感技术及其应用[D]. 中国科学院上海光学精密机械研究所. 2013. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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