【作者】 周会娟；

【导师】 孟洲；

【作者基本信息】 国防科学技术大学 ， 光学工程， 2012， 博士

【摘要】 分布式光纤传感器可实现长距离、大范围、多参量的传感，在关系国防和人们群众生命财产安全的安防、油气输运管道、电力网络、舰船飞机及大型建筑物的结构健康监控等方面有着显著的技术优势和广阔的应用前景。在各种分布式光纤传感技术中，基于布里渊散射的分布式光纤传感技术能够实现光纤沿线温度应变的长距离、大动态、高精度连续检测，获得了国内外研究人员的广泛关注，已成为发达国家掌握的一项高新科学技术，国内的相关研究还比较滞后。论文深入研究了光纤中的布里渊散射及其传感机理，进行布里渊分布式光纤传感系统的功率预算；在此基础上，自主研制了基于受激布里渊散射（SBS）的分布式光纤传感系统（BOTDA）；将该系统应用于某光纤水听器系统传输光缆的应力分布检测，实现了光缆的连续、在线受力状态分析；结合偏振分束器（PBS）将该系统应用于保偏光纤的均匀性检测，尤其保偏光纤陀螺环的绕制均匀性检测，使得陀螺环内部的光纤绕制状态直观可视；针对BOTDA系统中电光调制器微波移频存在的多边带和功率不稳定问题，创新性地利用DFB半导体激光注入锁定技术提取了稳定的具有布里渊频移的单频单边带；为了降低系统成本，深入研究了布里渊掺铒光纤激光器（BEFL），设计并实现了超短环形腔（~10m）BEFL，搭建了基于BEFL的BOTDA系统，验证了BEFL应用于布里渊传感系统的可行性。论文的主要研究成果和创新点如下：1、进行布里渊分布式光纤传感系统的功率预算。理论和实验研究了光纤的SBS阈值，得到了适合BOTDR系统的入射光功率上限，即后向散射光功率等于入射的泵浦光功率的1%时对应的泵浦光功率；通过仿真分析不同注入光功率下的泵浦光、Stokes光和布里渊增益沿光纤的分布，研究表明增益型BOTDA系统的泵浦光功率取值要大小合适，在泵浦光功率给定的情况下，探测光功率应尽可能小，以保证BOTDA系统中布里渊增益沿光纤的均匀分布同时维持一定的信噪比。这对布里渊分布式光纤传感系统具有重要的指导意义。2、自主研制了基于微波电光移频的BOTDA系统，通过温度和应变传感实验，标定出某单模光纤的温度系数和应变系数分别为1.01MHz/℃和0.57MHz/g（用重量表示），在25km的传感光纤上实现了1m的空间分辨率和优于0.5℃的温度测量精度。3、利用DFB半导体激光注入锁定技术提取了稳定的具有布里渊频移的单频单边带。针对BOTDA系统中电光调制器微波移频存在的多边带和功率不稳定问题，研究了DFB半导体激光注入锁定技术，结果表明处于弱注入锁定的从激光器能够起到窄带滤波器的作用，基于此将电光调制器移频后的光波注入从激光器，实现了稳定的具有布里渊频移的单频单边带的提取，该技术能够有效改善BOTDA系统的性能。4、首次将BOTDA系统应用于某光纤水听器系统传输光缆的连续、在线应力分布测试。将某光纤水听器系统传输光缆中的两根冗余光纤接入BOTDA系统，通过测试光缆的布里渊频移分布，分析了光缆在承受探头重量时及承重前后的应力分布状态，有助于光纤水听器系统的研制。该系统还可应用于光纤水听器湖上海上试验时的在线光缆状态监控。5、实现了保偏光纤陀螺环的绕制均匀性检测。利用偏振分束器（PBS）改进已有的BOTDA系统，保证BOTDA系统的泵浦光和探测光都被调制为线偏光且注入保偏光纤的同一主轴，实现了保偏光纤两轴各自的布里渊频移测试，利用该改进的BOTDA系统测试了两个保偏光纤陀螺环某一轴的布里渊频移分布，由于温度恒定，陀螺环的布里渊频移分布准确反映了环内部的应力分布，使得陀螺环内部的光纤绕制状态直观可视，据此对陀螺环进行初步筛选，有助于光纤陀螺的精度控制。6、首次提出并实现了超短环形腔（~10m）BEFL。这种激光器基于布里渊泵浦预放大技术，仅使用5m单模光纤提供非线性的布里渊增益，4m掺铒光纤提供线性EDFA增益；继续深入研究，设计并实现了紧凑型BEFL，该激光器仅采用4m掺铒光纤既提供布里渊增益又提供EDFA增益。由于BEFL输出光频相比其泵浦光频率下移了布里渊频移，可将其用于构建新型低成本的布里渊分布式光纤传感系统。更多还原

【Abstract】 Distributed optical fiber sensors allow long-haul, large-dynamic andmulti-parameter measurement. This kind of sensor has found technical superiority andwide applications in the fields which relate to national defense and people life andwealth safety, such as safety defence, oil and gas pipeline, electric power network,structure health monitoring of ships, airplanes, and civil structures. Among all thesesensors, distributed optical fiber sensors based on Brillouin scattering have gainedglobal interest for their ability to allow long-haul, large dynamic, and high precisiontemperature and strain measurement along the fiber. At present, this kind of sensor hasbeen an advanced technology that the developed countries hold. Nevertheless, there stillhas a lot of work to do for the domestic research.Firstly, Brillouin scattering in fibers and its sensing principle are analyzed in detail;power estimation of the Brillouin distributed fiber sensing systems is implemented.Then, a distributed sensing system based on stimulated Brillouin scattering (SBS)(i.e.,a BOTDA system) is designed and constructed. This system is applied to monitor thestrain distribution of the optical transmission cable of some fiber optic hydrophone(FOH) system; consecutive and in-line strain monitoring of the cable is realized.Polarization beam splitters (PBSs) are used to upgrade the BOTDA system, which isused to measure the uniformity of polarization-maintaining (PM) fibers. In particular,this upgraded system is applied to inspect the winding uniformity of PM fiber opticgyroscopes (FOG), which makes winding state inside the FOG intuitionisticlyvisualized. Because the electro-optic modulator with microwave frequency modulationin the system brings problems of multi-sideband and power fluctuation, DFB laserinjection locking technology is adopted to generate stable single-sideband frequencywith Brillouin frequency shift. Brillouin-erbium fiber laser (BEFL) is deeplyinvestigated to cut the system cost. Ultra-short ring-cavity (~10m) BEFLs are realized.A BOTDA system with BEFL is constructed, which confirms the feasibility of applyingBEFL to Brillouin sensing systems.The main results are summarized as follows:1. Power estimation of Brillouin sensing systems is implemented. The SBSthreshold is investigated theoretically and experimentally. The upper input powerlimitation of the BOTDR system, i.e., the SBS threshold suitable for optical fibersensors, is achieved. This threshold is defined as the pump power whose1%is equal tothe backscattered power. The distribution of pump and Stokes powers as well asBrillouin gain along the fiber is simulated and analyzed under various injected powers,which is achieved by solving the SBS coupled wave equations numerically. Thesimulation indicates that an appropriate pump power value is needed. Once the pump power is chosen, the probe power should be low enough. Thus, the BOTDA system canachieve uniform Brillouin gain along the fiber at a certain signal-to-noise ratio (SNR).The power estimation is significant for constructing Brillouin sensing systems.2. A BOTDA system based on microwave electro-optic frequency shift is designedand constructed. The Brillouin frequency shift temperature and strain coefficients of thesensing single-mode fiber are1.01MHz/℃and0.57MHz/g (in weight), respectively.The spatial resolution is1m and the temperature resolution is better than0.5℃with asensing fiber length of25km.3. DFB laser injection locking technique is used to extract stable single-sidebandfrequency with Brillouin frequency shift. Because the electro-optic modulator withmicrowave frequency modulation in the system brings problems of multi-sideband andpower fluctuation, DFB semiconductor laser injection locking technique is investigated.The results indicate that the locked slave laser under weak injection acts as anarrow-bandwidth optical filter. On account of thin point, the frequency-shifted lightafter the EOIM is injected into the slave laser and stable single side-band frequencywith Brillouin frequency shift is obtained, which can improve the BOTDA systemperformance.4. The BOTDA system is for the first time applied to realize consecutive andin-line strain monitoring of the optical transmission cable of some FOH system. Twoidle fibers inside the cable are connected to the BOTDA system. The strain distributionof the cable before and after hanging hydrophone is analyzed through Brillouinfrequency shift measurement, which is beneficial to FOH design. The BOTDA systemcan also be used to monitor cable state during FOH test over lakes and seas.5. Winding uniformity inspection of PM-FOG coils is realized. PBSs are used toupgrade the BOTDA system, which guarantee that the pump and probe light are bothlinearly polarized and injected into the same axis of PM fibers. Thus, the Brillouinfrequency shift distribution of the two axes can be measured, respectively. Theupgraded BOTDA system is applied to measure the Brillouin frequency shiftdistribution of some axis of PM-FOG coils. Because the temperature is constant, thestrain distribution inside the coils is exclusively and accurately decided by the measuredBrillouin frequency shift. Consequently, the winding uniformity of FOG coils isintuitionisticly visualized. The primary FOG coil screening is thus made, which issignificant for the FOG precision control.6. Ultra-short ring-cavity (~10m) BEFLs are for the first time designed andconstructed. There are two ways to realize this kind of lasers. The first is based onBrillouin pump pre-amplification. Only5m single-mode fiber and4m erbium-dopedfiber are used to provide the nonlinear Brillouin gain and linear EDFA gain,respectively. The second one only uses4m erbium-doped fiber which provides both nonlinear Brillouin gain and linear EDFA gain. Because the BEFL frequency is nativelyBrillouin frequency shift lower than its pump frequency, it can be used to constructnovel low-cost Brillouin distributed fiber sensing systems.更多还原