布里渊光时域分析仪（BOTDA）因其长距离分布式传感的优势而得到学术界和产业界的广泛研究与应用，光脉冲编码技术可以在不牺牲空间分辨率和测量时间的前提下辅助BOTDA进一步实现可观的信噪比提升，被认为是最高效（高信噪比提升和低硬件成本）的性能提升方法之一，具有显著的优势和应用前景。本文围绕基于光脉冲编码技术的BOTDA，介绍了用于分布式光纤传感领域的几种主流的光脉冲编码技术的原理，综述了近些年基于光脉冲编码的BOTDA传感系统的研究进展。

提出一种用于声波方向检测的弱反射光纤布拉格光栅(WFBG)分布式传感器,并进行了实验验证。将两个相邻WFBG间的分布式传感光纤用于检测声波振动信号。两段传感光纤解调的信号相位差对应于声波到达的时间差,再由时间差计算得到声波方向。一段长50 m的传感光纤环放置于振动液柱内,测得其平均声压灵敏度为-155.10 dB(re rad/μPa);两段50 m的传感光纤分布放置在木地板上用于接收正弦声波,探测方向的均方根误差为1.35°。理论推导和实验结果表明,这种分布式传感器能够实现对声波方向的检测,与传统基底缠绕光纤结构相比尺寸超细,有望搭载在水下无人航行器上,实现对水下发声目标的探测。

光纤形状传感技术是近年来光纤传感领域一个新的研究方向, 光纤形状传感器利用若干路在空间上具有特定排布的光纤组合在一起测量光纤或与之相连的被测物体的位置和形状。由于它具有不受电磁干扰、易于集成、形状测量精度高的特点, 可应用于医疗微创介入手术导管位置追迹、航天领域关键结构体形态测量、长距离管道及缆线变形监测等场合。本文论述了光纤形状传感技术在相关领域的应用, 综述了这一技术在国内外的最新研究进展, 对光纤形状传感的关键技术进行了详细的介绍, 同时分析了现有光纤形状传感技术所面临的主要瓶颈及误差来源。

铁路隧道防护门是隧道防灾救援专题的重要分支, 对行车安全有着重要的影响。文中研究一种基于微结构光纤分布式传感(MFDS)的新型铁路隧道防护门智能监测技术, 可以实时监测防护门的状态与检测运行故障, 当发现防护门出现异常状况时及时报警, 显示并记录报警部位和报警资料以及实现报警信号远程传送。通过研究, 针对铁路隧道防护门设计得出以下结论: (1) 防护门布置应采取远离隧道中心布置的方案; (2) 防护门隔墙应采用混泥土隔墙; (3) 防护门应朝疏散方向开启; (4) 设计防护门外沿距离相邻线路中心线距离应考虑防护门门框高度和车辆建筑限界。论文提出一种新颖的铁路隧道防护门设计方案, 对于铁路隧道防护门设计与维护相关工作具有重要指导意义。

在保偏光纤两端同一偏振方向上注入两束泵浦光, 产生受激布里渊散射并激发出相干声波场, 该声波场会对介质折射率进行调制, 即形成布里渊动态光栅。利用该动态光栅可实现温度与应变高精度的分布式测量以及多参量的同时传感, 并具有读写分离、光谱可调等优点。文章从原理上详细介绍了布里渊散射与布里渊动态光栅的产生原理, 并对比分析了布里渊动态光栅在光纤传感方面的优势。针对现阶段布里渊动态光栅在布里渊光相干域与布里渊光时域中的应用进行详细综述, 指出了各自的不足与改进后取得的进展。最后, 对布里渊动态光栅在分布式光纤传感技术中的发展进行了总结与展望。

为了解决分布式光纤振动传感系统中多点同时扰动情况下扰动点定位和扰动时间难以判断的问题, 采用信号处理方法, 应用聚类分析技术, 对系统生成的热点图先做阈值处理, 提取目标对象, 依聚类分析的结果, 对扰动点进行定位和扰动时间加以确认。结果表明, 该方法在排除噪声干扰的同时, 较为准确、合理地对扰动行为的位置和扰动持续时间做出了判断。这属于事件等级划分的一个步骤, 该研究为最终系统报警策略的规划提供了依据。

介绍了一种基于时分复用光纤传感技术的准分布折射率传感器。通过测量光纤端面的菲涅耳反射信号的强度，实现对待测溶液折射率的分布检测。在多个测量点之间采用不同长度的延迟光纤，利用不同传感位置处的菲涅耳反射信号回到测量端的时间差来实现距离可分辨的多点测量。实验结果表明该传感器的测量距离达16 km，测得折射率范围为1.3486~1.4525，对应的灵敏度范围为38.785~305.430 dB/RIU(RIU 为折射率单元)。

In this paper, we review our researches on the topics of the structural health monitoring (SHM) with the fiber-optic distributed strain sensor. Highly-dense information on strains in a structure can be useful to identify some kind of existing damages or applied loads in implementation of SHM. The fiber-optic distributed sensors developed by the authors have been applied to the damage detection of a single-lap joint and load identification of a beam simply supported. We confirmed that the applicability of the distributed sensor to SHM could be improved as making the spatial resolution higher. In addition, we showed that the simulation technique considering both structural and optical effects seamlessly in strain measurement could be powerful tools to evaluate the performance of a sensing system and design it for SHM. Finally, the technique for simultaneous distributed strain and temperature measurement using the PANDA-fiber Bragg grating (FBG) is shown in this paper, because problems caused by the cross-sensitivity toward strain and temperature would be always inevitable in strain measurement for SHM.

Different types of fiber-optic sensors based on glass or polymeric fibers are used to evaluate material behavior or to monitor the integrity and long-term stability of load-bearing structure components. Fiber-optic sensors have been established as a new and innovative measurement technology in very different fields, such as material science, civil engineering, light-weight structures, geotechnical areas as well as chemical and high-voltage substations. Very often, mechanical quantities such as deformation, strain or vibration are requested. However, measurement of chemical quantities in materials and structure components, such as pH value in steel reinforced concrete members also provides information about the integrity of concrete structures. A special fiber-optic chemical sensor for monitoring the alkaline state (pH value) of the cementitious matrix in steel-reinforced concrete structures with the purpose of early detection of corrosion-initiating factors is described. The paper presents the use of several fiber-optic sensor technologies in engineering. One example concerns the use of highly resolving concrete-embeddable fiber Fabry-Perot acoustic emission (AE) sensors for the assessment of the bearing behaviour of large concrete piles in existing foundations or during and after its installation. Another example concerns fiber Bragg grating (FBG) sensors attached to anchor steels (micro piles) to measure the strain distribution in loaded soil anchors. Polymer optical fibers (POF) can be — because of their high elasticity and high ultimate strain - well integrated into textiles to monitor their deformation behaviour. Such “intelligent” textiles are capable of monitoring displacement of soil or slopes, critical mechanical deformation in geotechnical structures (dikes, dams, and embankments) as well as in masonry structures during and after earthquakes.

The distributed sensor is proven to be a powerful tool for civil structural and material process monitoring. Brillouin scattering in fiber can be used as point sensors or distributed sensors for measurement of temperature, strain, birefringence and vibration over centimeters (Brillouin grating length) for point sensor or the pulse length for the distributed sensor. Simultaneous strain and temperature measurement with a spatial resolution of 20 cm is demonstrated in a Panda fiber using Brillouin grating technique with the temperature accuracy and strain accuracy of 0.4 ℃ and 9 με. This technique can also be used for distributed birefringence measurement. For Brillouin optical time domain analysis (BOTDA), we have developed a new technique to measure differential Brillouin gain instead of Brillouin gain itself. This technique allows high precision temperature and strain measurement over long sensing length with sub-meter spatial resolution: 50-cm spatial resolution for 50-km length, using return-to-zero coded optical pulses of BOTDA with the temperature resolution of 0.7 ℃, which is equivalent to strain accuracy of 12 με. For over 50-km sensing length, we proposed and demonstrated frequency-division-multiplexing (FDM) and time-division-multiplexing (TDM) based BOTDA technique for 75-km and 100-km sensing length without inline amplification within the sensing length. The spatial resolution of 2 m (100 km) and Brillouin frequency shift accuracy of 1.5 MHz have been obtained for TDM based BOTDA and 1-m resolution (75 km) with Brillouin frequency shift accuracy of 1 MHz using FDM based BOTDA. The civil structural health monitoring with BOTDA technique has been demonstrated.