高精度分布式光纤传感及相关信号解调技术的研究
发布时间：2018-08-17 16:01
【摘要】：近年来,以光纤中散射光为传感载体的分布式光纤传感器以其独特的优势,在传感领域内得到众多研究者的青睐。如光纤传感和传输集于一身的优势,可实现温度和应力等多参量的同时监测,并能实现全方位智能监测,从而克服传统点式监测漏检的弊端,提高监测的成功率等。基于布里渊光时域反射技术(BOTDR)单端测量的特性便于实际应用,是目前国内外研究的热点之一。在BOTDR分布式光纤传感技术中,以相干检测的传感精度最高,在大型工程如石油天然气管道泄露、大型混凝土结构(大坝、隧道、建筑物等)等的健康监测方面具有广泛的应用前景。由于布里渊散射光光功率十分微弱,容易淹没在噪声中,且频移比较小,信号检测非常困难,因此研究信号解调方法,提高信号解调精度,对系统测量的精准性和可靠性尤为重要。 本文在深入研究布里渊散射机理的前提下,提出一套切实可行的基于自发布里渊散射的分布式光纤温度应变传感系统方案,以提高信号解调精度为重点进行逐步研究,在该过程中进行一系列的实验验证和测试。该系统方案采用外差相干检测方法,激光器发出窄线宽的连续光分成90：10两部分,90%连续光经光电调制器调制成脉冲光之后采用掺饵光纤放大器进行放大,然后注入传感光纤以产生布里渊后向散射脉冲信号；10%的连续光经电光调制器产生移频边带,通过加载在电光调制器的微波扫频源和直流偏置电压的调制,获取具有布里渊频移的参考光。背向布里渊散射光经光纤光栅滤波后与参考光在光电探测器处相干进入信号处理系统,进行去噪处理和计算分析,获取温度和应力在传感光纤的分布情况。 本文采取一系列措施提高系统测量精度：(1)在参考路获取参考光方面,本系统采用电光调制器产生的两个1阶边带作为布里渊频移的参考光,获取具有高1阶边带与0阶边带光强差(1-0光强比)的参考光,是系统的信号解调的关键。第一,详细研究了偏振对电光调制器产生边带的光强的影响,提出了偏振控制器与直流偏置电压结合的方式获取高1-0光强差的参考光。第二,采用步进为1MHz的微波扫频源进行自动微波扫频,找到最佳参考光频率,提高系统信号解调精度。(2)在探测路提取布里渊信号方面,首先,使用本底噪声较小的放大器,提高信号信噪比。其次,运用滤波精度达到0.001nm/℃可调温控光纤光栅滤波技术提取斯托克斯信号光,提高系统信号解调精度(3)在信号相干处理系统方面,先采用自外差相干探测法解调信号,将太赫兹数量级的布里渊高频信号降至易于探测和处理的百兆赫兹数量级的中频信号,提高了系统的探测精度。再运用LabVIEW分析处理去除噪声等措施,提高系统信号解调精度等等,增强系统的稳定性和可靠性,降低了系统的成本。最后,进行了一系列的实验研究和系统测试及结果分析。具体地说,全文包括以下几个方面： 第一章绪论,简单介绍了分布式光纤传感的基本知识,包括分布式光纤传感技术的特点,分布式光纤技术的分类,和基于布里渊散射的光纤传感技术(BOTDR、BOTDA、BOFDA),然后综述了本文主要研究的基于自发布里渊散射光纤传感技术的研究现状和课题意义及研究目标,最后介绍了本文所做的主要工作。 第二章是研究课题的理论部分,首先介绍了光纤中的散射现象和三种散射谱,阐述了自发和受激布里渊散射的产生机理,从理论上分析了光纤应变和温度与布里渊频移和散射强度的变化关系,根据光纤中的自发布里渊散射的频移和强度受光纤温度和应变影响的机理,得到了利用光纤布里渊散射进行温度和应变同时测量的传感模型,为BOTDR系统的设计奠定了理论基础。 第三章介绍偏振与获取高光强的参考光,是本文的核心研究内容之一。详细研究了电光调制器的移频特性,从理论和实验两方面研究了偏振对EOM调制的光波边带光强的影响。提出边带光强随偏振的改变呈现cos2x的变化趋势,实验结果与理论预测相符。提出使用偏置电压和偏振控制相结合的方法得到稳定的,1-0光强差为24dB的参考光,比仅仅调偏置电压时高18dB,使用该参考光明显提高了系统信噪比,提高系统信号解调精度。 第四章系统测试及实验结果分析,是本论文另一核心内容。包括系统的整体搭建,各子系统中器件和实验参数的选取,以及系统温度传感实验结果讨论与LabVIEW分析处理等。选择本底噪声低的放大器,运用滤波精度达到0.001nm/℃的可调温控光纤光栅滤波技术提取斯托克斯光,和采用自动微波扫频等方法提高了系统信号解调精度。实验中频谱分析仪采集到的波峰频率为10.853GHz,与布里渊频移的理论值相符。在系统温度传感实验中得到的温度系数为1.0843MHz/℃,该实验数据接近于前人报道的数据1.2MHz/℃,它们之间的差值主要是由于仪器误差。采用LabVIEW软件分析处理了布里渊散射强度信号,详细阐述了累加平均去噪、小波去噪和低通滤波去噪的原理,并对了三种去噪方法的处理效果。 第五章总结与展望,对本论文进行总结,分析该系统存在的不足之处,指出下一步需继续进行的研究。
[Abstract]:In recent years, distributed optical fiber sensors based on scattered light in optical fibers have been favored by many researchers for their unique advantages. For example, the advantages of optical fiber sensing and transmission are integrated, which can realize simultaneous monitoring of temperature and stress, and realize omnidirectional intelligent monitoring, thus overcoming the traditional points. Based on the characteristics of Brillouin Optical Time Domain Reflectometry (BOTDR), which is convenient for practical application, is one of the research hotspots at home and abroad. The Brillouin scattered light is very weak and easy to be submerged in the noise, and the frequency shift is small, so it is very difficult to detect the signal. Therefore, the signal demodulation method is studied to improve the signal demodulation accuracy and the accuracy of system measurement. And reliability is particularly important.
On the premise of thorough study of Brillouin scattering mechanism, a feasible scheme of distributed optical fiber temperature and strain sensor system based on spontaneous Brillouin scattering is proposed in this paper. The emphasis is to improve the signal demodulation accuracy, and a series of experiments are carried out to verify and test the system. In dry detection, the laser emits a narrow-linewidth continuous light which is divided into two parts: 90:10, 90% of which is modulated into pulse light by a photoelectric modulator, then amplified by a bait-doped fiber amplifier, and then injected into a sensing fiber to generate Brillouin backscattering pulse signal; 10% of the continuous light generates a frequency-shift sideband via an electro-optic modulator and adds a frequency-shift sideband through an electro-optic modulator. The reference light with Brillouin frequency shift is obtained by modulating the microwave sweep source and the DC bias voltage loaded on the electro-optic modulator. The back Brillouin scattered light filtered by the fiber grating is coherent with the reference light at the photoelectric detector to enter the signal processing system for denoising processing and calculation analysis, and the temperature and stress in the sensing fiber are obtained. Cloth situation.
In this paper, a series of measures are taken to improve the measurement accuracy of the system: (1) In the reference path, two first-order sidebands generated by electro-optic modulators are used as Brillouin frequency-shift reference beams, and the reference beams with high first-order sideband and zero-order sideband intensity difference (1-0 intensity ratio) are obtained. This is the key to the signal demodulation of the system. The influence of polarization on the intensity of side-band light produced by electro-optic modulator is studied in detail, and a method combining polarization controller with DC bias voltage is proposed to obtain the reference light with high 1-0 light intensity difference. In the aspect of extracting Brillouin signal, firstly, the amplifier with less background noise is used to improve the signal-to-noise ratio. secondly, the Stokes signal is extracted by using the temperature-adjustable fiber grating filtering technology with filtering accuracy of 0.001 nm / The detection method demodulates the signal, reduces the Brillouin high frequency signal of terahertz order to the intermediate frequency signal of 100 MHz order which is easy to be detected and processed, improves the detection precision of the system, improves the demodulation precision of the system signal and so on, enhances the stability and reliability of the system, reduces the detection precision by using LabVIEW analysis and processing to remove the noise. Finally, a series of experimental studies and system testing and results analysis are carried out. Specifically, the full text includes the following aspects:
In the first chapter, the basic knowledge of distributed optical fiber sensing is briefly introduced, including the characteristics of distributed optical fiber sensing technology, the classification of distributed optical fiber technology, and the Brillouin scattering-based optical fiber sensing technology (BOTDR, BOTDA, BOFDA). Then the research of this paper based on self-issued Brillouin scattering optical fiber sensing technology is summarized. The status quo, the significance of the project and the research objectives are introduced. Finally, the main work of this paper is introduced.
The second chapter is the theoretical part of the research project. Firstly, the scattering phenomena and three kinds of scattering spectra in optical fibers are introduced. The mechanism of spontaneous and stimulated Brillouin scattering is expounded. The relationship between strain and temperature of optical fibers and Brillouin frequency shift and scattering intensity is analyzed theoretically. The sensing model of temperature and strain simultaneous measurement by fiber Brillouin scattering is obtained, which lays a theoretical foundation for the design of BOTDR system.
In the third chapter, polarization and obtaining high-intensity reference light are introduced, which is one of the core research contents of this paper. The frequency-shift characteristics of electro-optic modulator are studied in detail. The influence of polarization on the intensity of EOM-modulated optical sideband is studied theoretically and experimentally. Theoretical predictions are consistent. A stable reference light with a 1-0 intensity difference of 24 dB is obtained by combining bias voltage with polarization control. The reference light is 18 dB higher than that by only adjusting the bias voltage. The signal-to-noise ratio of the system is obviously improved and the demodulation accuracy of the system signal is improved by using the reference light.
Chapter 4: System test and experiment result analysis, which is another core content of this paper, includes the whole structure of the system, the selection of devices and experiment parameters in each subsystem, the discussion of system temperature sensing experiment results and LabVIEW analysis and processing. The demodulation precision of the system signal is improved by using the technique of controlling fiber grating filter to extract Stokes light and the method of automatic microwave sweeping. The peak frequency of the spectrum analyzer is 10.853GHz, which is in agreement with the theoretical value of Brillouin frequency shift. According to the data close to 1.2MHz/C reported by predecessors, the difference between them is mainly due to instrumental error. Brillouin scattering intensity signal is analyzed and processed by LabVIEW software. The principles of cumulative average denoising, wavelet denoising and low-pass filtering denoising are expounded in detail, and the processing effects of three denoising methods are given.
The fifth chapter summarizes and prospects the paper, analyzes the shortcomings of the system, and points out the further research.
【学位授予单位】：东华大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TP212;TN911.7
本文编号：2188165
[Abstract]:In recent years, distributed optical fiber sensors based on scattered light in optical fibers have been favored by many researchers for their unique advantages. For example, the advantages of optical fiber sensing and transmission are integrated, which can realize simultaneous monitoring of temperature and stress, and realize omnidirectional intelligent monitoring, thus overcoming the traditional points. Based on the characteristics of Brillouin Optical Time Domain Reflectometry (BOTDR), which is convenient for practical application, is one of the research hotspots at home and abroad. The Brillouin scattered light is very weak and easy to be submerged in the noise, and the frequency shift is small, so it is very difficult to detect the signal. Therefore, the signal demodulation method is studied to improve the signal demodulation accuracy and the accuracy of system measurement. And reliability is particularly important.
On the premise of thorough study of Brillouin scattering mechanism, a feasible scheme of distributed optical fiber temperature and strain sensor system based on spontaneous Brillouin scattering is proposed in this paper. The emphasis is to improve the signal demodulation accuracy, and a series of experiments are carried out to verify and test the system. In dry detection, the laser emits a narrow-linewidth continuous light which is divided into two parts: 90:10, 90% of which is modulated into pulse light by a photoelectric modulator, then amplified by a bait-doped fiber amplifier, and then injected into a sensing fiber to generate Brillouin backscattering pulse signal; 10% of the continuous light generates a frequency-shift sideband via an electro-optic modulator and adds a frequency-shift sideband through an electro-optic modulator. The reference light with Brillouin frequency shift is obtained by modulating the microwave sweep source and the DC bias voltage loaded on the electro-optic modulator. The back Brillouin scattered light filtered by the fiber grating is coherent with the reference light at the photoelectric detector to enter the signal processing system for denoising processing and calculation analysis, and the temperature and stress in the sensing fiber are obtained. Cloth situation.
In this paper, a series of measures are taken to improve the measurement accuracy of the system: (1) In the reference path, two first-order sidebands generated by electro-optic modulators are used as Brillouin frequency-shift reference beams, and the reference beams with high first-order sideband and zero-order sideband intensity difference (1-0 intensity ratio) are obtained. This is the key to the signal demodulation of the system. The influence of polarization on the intensity of side-band light produced by electro-optic modulator is studied in detail, and a method combining polarization controller with DC bias voltage is proposed to obtain the reference light with high 1-0 light intensity difference. In the aspect of extracting Brillouin signal, firstly, the amplifier with less background noise is used to improve the signal-to-noise ratio. secondly, the Stokes signal is extracted by using the temperature-adjustable fiber grating filtering technology with filtering accuracy of 0.001 nm / The detection method demodulates the signal, reduces the Brillouin high frequency signal of terahertz order to the intermediate frequency signal of 100 MHz order which is easy to be detected and processed, improves the detection precision of the system, improves the demodulation precision of the system signal and so on, enhances the stability and reliability of the system, reduces the detection precision by using LabVIEW analysis and processing to remove the noise. Finally, a series of experimental studies and system testing and results analysis are carried out. Specifically, the full text includes the following aspects:
In the first chapter, the basic knowledge of distributed optical fiber sensing is briefly introduced, including the characteristics of distributed optical fiber sensing technology, the classification of distributed optical fiber technology, and the Brillouin scattering-based optical fiber sensing technology (BOTDR, BOTDA, BOFDA). Then the research of this paper based on self-issued Brillouin scattering optical fiber sensing technology is summarized. The status quo, the significance of the project and the research objectives are introduced. Finally, the main work of this paper is introduced.
The second chapter is the theoretical part of the research project. Firstly, the scattering phenomena and three kinds of scattering spectra in optical fibers are introduced. The mechanism of spontaneous and stimulated Brillouin scattering is expounded. The relationship between strain and temperature of optical fibers and Brillouin frequency shift and scattering intensity is analyzed theoretically. The sensing model of temperature and strain simultaneous measurement by fiber Brillouin scattering is obtained, which lays a theoretical foundation for the design of BOTDR system.
In the third chapter, polarization and obtaining high-intensity reference light are introduced, which is one of the core research contents of this paper. The frequency-shift characteristics of electro-optic modulator are studied in detail. The influence of polarization on the intensity of EOM-modulated optical sideband is studied theoretically and experimentally. Theoretical predictions are consistent. A stable reference light with a 1-0 intensity difference of 24 dB is obtained by combining bias voltage with polarization control. The reference light is 18 dB higher than that by only adjusting the bias voltage. The signal-to-noise ratio of the system is obviously improved and the demodulation accuracy of the system signal is improved by using the reference light.
Chapter 4: System test and experiment result analysis, which is another core content of this paper, includes the whole structure of the system, the selection of devices and experiment parameters in each subsystem, the discussion of system temperature sensing experiment results and LabVIEW analysis and processing. The demodulation precision of the system signal is improved by using the technique of controlling fiber grating filter to extract Stokes light and the method of automatic microwave sweeping. The peak frequency of the spectrum analyzer is 10.853GHz, which is in agreement with the theoretical value of Brillouin frequency shift. According to the data close to 1.2MHz/C reported by predecessors, the difference between them is mainly due to instrumental error. Brillouin scattering intensity signal is analyzed and processed by LabVIEW software. The principles of cumulative average denoising, wavelet denoising and low-pass filtering denoising are expounded in detail, and the processing effects of three denoising methods are given.
The fifth chapter summarizes and prospects the paper, analyzes the shortcomings of the system, and points out the further research.
【学位授予单位】：东华大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TP212;TN911.7
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