【作者】 常天英；

【导师】 贾磊； 崔洪亮； 隋青美；

【作者基本信息】 山东大学 ， 检测技术与自动化装置， 2009， 博士

【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,比如传感光纤质轻柔软、抗电磁干扰、分布式测量以及传感传输集于一身等,在传感领域内得到众多研究者的青睐。完全分布式光纤传感系统主要有两种,一种是基于拉曼散射,另一种是基于布里渊散射。其中基于拉曼散射的分布式传感系统已被研究成熟,基本商业化;由于基于布里渊散射的分布式传感系统能够同时测量温度和应变两大参数,所以相比较基于拉曼散射的分布式传感系统更有优势,但由于布里渊散射光检测的困难性,致使发展不够成熟,至今未大规模商业化。本文在深入研究布里渊散射机理的前提下,详细分析前人研究的过程及方法之后,针对布里渊散射光检测的特点,提出一套切实可行并且有别于前人方法的基于布里渊散射的分布式光纤温度应变传感系统方案,据此对该系统进行逐步研发,在该过程中进行一系列的实验验证和测试,并且考虑相关的算法和影响因素,采取一定的措施。该系统方案简单来说是采用DFB(分布式反馈)激光器发出窄线宽的连续光后经光电调制器外调制成脉冲光,之后采用EDFA(掺铒光纤放大器)进行放大,被放大的脉冲光作为入射光进入传感光纤以获得该光纤中的布里渊后向散射信号。该方式采用单端输入的方式来获得布里渊散射信号,这样便于该系统的安装使用;提出了采用同源外差干涉法来解调信号,该方法避免了一般干涉法对两束光强度相近的要求,简化了测试系统;另外采取一定措施来加强信号,以便于后续处理;同时应用电的方式来同时得到布里渊频移和强度的变化,这样就可以对温度和应变进行解调,实现对二者的同时测量。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,在概述中简单介绍一些基本知识,包括光纤的传输特性,普通单模光纤中散射光的分类以及各自的定义,两种主要光纤传感技术:光纤光栅传感技术和分布式光纤传感技术(其中又包括基于瑞利散射、基于拉曼散射以及基于布里渊散射),然后综述了基于布里渊散射光纤传感技术的研究现状和课题意义,最后介绍了本文所做的主要工作。第二章布里渊散射及其传感技术的理论基础,是研究课题的理论部分,从理论上分析布里渊散射的一系列特性。具体来说,本章详细介绍普通单模光纤中布里渊散射的分类以及各自产生的机理;并且分析其光谱的特性,包括布里渊频移的大小、谱图形状、强度分布等;最后阐述如何实现对传感光纤所受温度和应变的测量。第三章基于布里渊散射的分布式光纤传感系统,本毕业论文的两大核心内容之一,包括系统结构、系统方法、关键器件性能分析和使用、软件开发以及实验平台。在系统结构中,给出系统的总体介绍,描述信号的流程;在系统方法中,介绍了系统中所使用的四种独特方法,包括同源外差干涉解调布里渊信号的基本原理和独特优势;加强信号的两种方法,一是双脉冲法增强布里渊散射信号,另一个是加强外差干涉中的瑞利成份;电方法解调温度和应变的结构图、理论依据和计算方法;布里渊光强度的归一化计算方法以及系统性能指标分析;在关键器件性能分析和使用中,对系统中的主要器件进行较详细的介绍,包括性能指标,选定原则以及周围电路控制原理等;软件开发部分,就该系统的具体要求,叙述对数据采集卡的软件控制、数据流程以及平均计算过程等相关内容;在实验平台中给出整套系统的实物图片;最后作了一小结。第四章实验研究,包括掺铒光纤放大器的研究、入射光参数变化对后向散射光谱图影响的研究以及非线性现象的研究。具体来说,即针对本系统的要求,给出掺铒光纤放大器的实验研究;通过调整入射光的参数来研究光纤后向散射光与入射光的关系;若入射光参数合适的时候,光纤非线性现象的出现,通过大量实验来验证其规律性和相关因素的影响,最后剖析其产生的可能原因。第五章系统测试及结果分析,是本论文另一核心内容。在信号测试中,用频谱分析仪测试得到外差干涉的高频信号,用示波器得到表征沿光纤分布的散射光的特征信号;并且给出对普通单模光纤所受温度、应变的测试结构、过程以及结果。在以上的实验中得到频谱分析仪上波峰频率为10.8420GHz,与布里渊频移的理论值相符,示波器上的两路波形反映了沿光纤传输的后向散射光信息,在温度实验中得到的升温和降温的关系系数分别为1.0843 MHz/℃和1.0462 MHz/℃,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,在应变实验中得到的室温下的关系系数为0.049MHz/με,与前人报道的数据一致,这些实验表明了整个系统的可行性和准确性。第六章总结与展望,对本论文进行总结,并且分析该系统存在的问题,指出针对该系统需继续进行的研究和试验,最后展望未来且预测该系统远大的应用前景。更多还原

【Abstract】 Recently, the distributed fiber sensor based on scattering light has many merits, such as light and soft, resistance to electromagnetic interference, easy to carry out the distributed measurement, sensing and transmission in one fiber, and so on, so that it is pretty popular in sensing field. The absolute distributed fiber sensing system mainly has two kinds: one is based on Raman scattering and the other is based on Brillouin scattering. Thereinto, the distributed fiber sensing system based on Raman has been researched deeply and is basically commercial now; on the other hand, the distributed fiber sensing system based on Brillouin scattering can measure temperature and strain simultaneously so it is more attractive compared with that based on Raman scattering, but the detection of Brillouin scattering light is difficult so that its development is slow and has not been commercial up to today.In this dissertation, Brillouin scattering mechanism was researched deeply and the previous research process and method were analyzed in detail. After that, considering the characteristics of Brillouin scattering light detection, we proposed a feasible and novel scheme of distributed optical fiber temperature and strain sensing system based on Brillouin scattering. According to this scheme, the system was built step by step and the corresponding experiments and tests were done. In consideration of related calculation and influencing factors, the measurements had been taken. Simply speaking, our method is as following: narrow-linewidth continuous light from a distributed feedback laser (DFB-laser) is modulated into pulse light by the photoelectrical modulator. The pulse light is amplified by Er-doped fiber amplifier (EDFA). After that, it enters the sensing fiber and makes Brillouin backscattering light generate. There are several keys in our work. Firstly, the Brillouin scattering light is obtained through single-input which makes the system installation convenient. Secondly isogenous heterodyne interference is put forward in the first time to demodulate Brillouin backscattering signal which avoids the disadvantage of the general interference method demanding two component lights’ intensity approach, and simplifies the testing system. Thirdly, the measurement has been taken to strengthen the signal in order to simplify the later signal process. Fourthly, the Brillouin frequency shift and intensity variance can be obtained at the same time by the electrical method. Thus the temperature and strain can be gotten simultaneously. Lastly, a series of experiment research and system testing result analysis are mode. Concretely, the main text includes the following aspects.In Ch1 introduction, summary introduces basal knowledge, including fiber’s transmission characteristics, scattering light classification in single-mode fiber and their definitions, two kinds fiber sensing technologies (Fiber grating sensing technology and distributed fiber sensing technology which includes those based on Rayleigh scattering, based on Raman scattering and based on Brillouin scattering). Then, fiber sensing technology based on Brillouin scattering research status quo and subject signification is displayed. Lastly, the main task in this dissertation is introduced simply.In Ch2 theory basis of Brillouin scattering and its sensing technology which is theoretical part of the research object, the Brillouin scattering characteristics are analyzed in theory. The category of the Brillouin scattering and their generation principles are introduced. And the spectrum characteristics which include the Brillouin frequency shift, spectrum shape, and intensity distribution, are analyzed. Lastly, it is described how to measure temperature and strain suffered by the sensing fiber.In Ch3 distributed fiber sensing system based on Brillouin scattering is one of the dissertation’s two cores, including system structure, system methods, key components performance analysis and usage, software development and experiment platform. Firstly, in system structure, the system is introduced on the whole and the signal flow is described. Secondly, in system methods, four special methods in the system are introduced, including the basal principle and advantages of the isogenous heterodyne interference used to detect the Brillouin signal, the methods to strengthen the signal, which are double-pulse strengthening Brilliouin scattering signal and making Rayleigh component in heterodyne interference strengthening, the demodulation of temperature and strain by the electrical way including its structure, theory basis and calculation method, the normalization of the Brillouin intensity and system performance index analysis. Thirdly, in key components performance analysis and usage, the main devices in this system are displayed in detail, including performance index, selection principle and circuit controller principle, and so on. Fourthly, in software development, according to the demands of this system, it depicts the software control to the digitizer, data flow, averaging process, and so on. Fifthly, in experiment platform, the picture of the whole system is shown. Lastly, the conclusion is given.In Ch4 experiment research, which includes research on Er-doped fiber amplifier (EDFA), research on the influence of incidence light parameters to backscattering light spectrum, and research on nonlinear phenomenon. Concretely speaking, the experimental research of the EDFA is done and the relationship between backscattering light and incidence light is gotten through adjusting the parameters of the incidence light. When parameters of incidence light are suitable, the fiber nonlinearity phenomenon occurs. The corresponding experiments are done to look for its rule and influencing factors. The possible reasons are given based on the above experiments.In Ch5 system testing and result analysis, is the other core in this dissertation. In signal testing, the high frequency signal of heterodyne interference is seen from the spectrum analyzer, the signal along the sensing fiber is gotten from the oscilloscope, and the temperature and strain testing experiments for single-mode fiber are done, which results are good. The peak frequency from the spectrum analyzer is 10.8420GHz, which is consistent with the theoretical value of Brillouin frequency shift. The two signal waveforms from the oscilloscope have the information of the backscattering light along the optical fiber. The temperature coefficients in the temperature elevation and reduction process are separately 1.0843 MHz/℃and 1.0462 MHz/℃, which are near to the data in the previous article which is 1.2MHz/℃and the little difference is caused by the apparatus error. The strain coefficient under room temperature is 0.049 MHz /με, which is consistent with thedata in the previous article. The above data indicate the system’s feasibility and veracity. In the calculation, the spatial resolution, light pulse power and signal to noise ratio are calculated.In Ch6 conclusion and prospect, the whole conclusion is given. The author analyzes the issues of this system and points out the research and experiment which should be gone on for this system in the future. In the end, the author prospects the future and forecasts the application foreground of the system.更多还原