【作者】 张威；

【导师】 孙琪真； 闫志君；

【作者基本信息】 华中科技大学 ， 光学工程， 2020， 博士

【摘要】 分布式光纤传感技术集传感与传输于一体,可获取沿光纤链路上随时间变化的多维信息数据,具有大容量、高灵敏度、小型化等优点,并且可以用于多种特殊环境中实现长期稳定的测量,其在精准制造、医疗健康、环境监测等领域具有很好的发展潜力。近年来,随着科技发展和社会进步,这些领域对传感空间分辨率的需求日益提升,需要达到厘米甚至毫米量级的分辨率,以获取更精细的多维信息数据。传统分布式光纤传感技术主要采用普通光纤作为传感载体,为了提升空间分辨率,在光源、光探测和信号处理技术等方面开展了许多研究工作,取得了良好的成效,但是也带来系统的复杂度和成本的提高。采用新型传感光纤是另一种有效提高传感空间分辨率的方法,可以针对不同应用场景灵活设计,并同时兼顾传感容量和传感距离。本论文工作主要围绕高空间分辨率的分布式光纤传感技术,从传感光纤设计和信号解析技术开展创新研究,分别针对超高分辨、超大容量和超长距离传感需求设计并研制了三种新型纵向微结构传感光纤,并以此为载体进行了分布式传感机理研究及传感系统开发和应用探索。论文主要内容包括:(1)针对高空间分辨率分布式传感需求,开展基于光纤纵向微结构改性的新型传感光纤基础理论与制备研究。研究光纤改性制备机理以及纵向微结构光纤的传感机理和信号解调技术。针对纵向微结构光纤制备工艺需求,设计放纤装置,收纤装置,应力控制装置等核心模块,开发多功能光纤微结构连续刻写平台,能够实现均匀和非均匀光纤光栅、微腔结构以及局部散射增强点等多种微结构沿光纤轴向的连续刻写和空间分布灵活调控。光纤的移动速度可在6mm/min～10000mm/min范围内精确调控,微结构刻写精度为5μm,可制备光纤最长距离达到50km,实现纵向微结构光纤的自动化批量制备。(2)针对超高空间分辨率的短距离分布式检测需求,提出并研究具有多信道特性的连续微结构光纤光栅及其传感技术。采用层剥离算法以及群时延调控方法设计空间上相互分离的多波长信道的连续微结构光纤光栅,并基于无缝紫外刻写技术实现21信道的连续微结构光纤光栅制备;研究多信道光栅的温度传感特性,提出了基于波长信道追踪的解调方法,对均匀温度场、梯度温度场、辐射温度场进行分布式传感的实验研究,实现了63mm范围内的实时温度场监测,空间分辨率达到3mm,最大可测量温度梯度为7.85℃/mm。(3)针对超大容量的高空间分辨率传感传感需求,提出了弱反Fabry-Perot(FP)微结构光纤及其分布式传感技术。设计具有波长和频率二维编码能力的弱反射FP微腔结构及其单纤复用方案,理论分析表明在10mm空间分辨率条件下可实现单纤243单元的复用,检测长度可达2430mm,相比于一维波长编码技术提高一个数量级;进一步,针对消化道动力监测对高压力灵敏度的需求,提出基于聚合物材料柔性封装的侧向压力增敏方法,建立理论模型并通过有限元分析方法仿真计算了封装材料的弹性模量、泊松比、直径等关键参数对压力的增敏规律,通过参数优化实现传感光纤对侧向压力的灵敏度提升700倍;研制了基于可调谐FP滤波器以及光谱傅里叶变换方法的传感解调终端,进行了静态和动态压力实验研究,实现了120cm/min的动态压力波监测,分布式压力传感空间分辨率可达10mm,压力灵敏度为2.2MPa/nm,压力分辨率0.46k Pa,压力传感范围0～40k Pa。(4)针对超长距离的高空间分辨率传感检测需求,提出了散射增强微结构光纤及其分布式传感技术。通过在光纤中构建等间距分布、强度渐变型的散射增强点突破系统动态范围对传感距离的限制,并进一步采用分段调控使得无中继传感距离达到90.5km;通过单脉冲激光曝光的方式在单模光纤纤芯上引入局部缺陷并结合连续绕纤方式,研制17km长的后向散射增强微结构光纤,实现后向散射信号强度提升约5d B。针对石油运输储存、废水处理等领域的大动态范围高精度液位监测需求,研究基于散射增强微结构光纤的高分辨率分布式液位传感技术。提出了基于气液接触面上气相和液相的温度突变效应的大范围液位监测技术,进一步通过缠绕式封装提高液位测量的灵敏度和空间分辨率,并结合相干相位解调技术实现高分辨率的动态液位测量,实验上获得了74μm的空间分辨率,基于制备的17km微结构光纤,液位测量范围可达85m。更多还原

【Abstract】 Distributed optical fiber sensing technology integrates sensing and transmission,which can obtain multi-dimensional information along the optical fiber varying with time.The technology has the advantages of large capacity,high sensitivity,miniaturization,and can be used in a variety of special environments to achieve long-term and stable measurement,which paves a promising way in the field of precision manufacturing,medical health,environmental monitoring etc.In recent years,with the development of technology and society,it is necessary to improve the sening spatial resolution to centimeter or even millimeter for more precise multi-dimensional sensing information.The traditional distributed optical fiber sensing technologies mostly adopt common optical fiber as the sensing carrier.In order to improve the spatial resolution,lots of researches have been studied in the light source,optical detection and signal processing method,which have obtained great achievement,but also result in the complexity and cost of the system.The utilization of novel sensing fiber is another effective way to improve the spatial resolution.This method is more flexible for different applications,which can improve the spatial resolution as well as take into account the sensing capacity and sensing distance.This paper focuses on the high spatial resolution distributed optical fiber sensing technology,and carries out innovative research from the sensing fiber and signal analysis technology.Three kinds of longitudinal microstructured fiber were studied for ultra-high resolution,large capacity and long distance sensing application as well as the distributed sensing mechanism and the sensing system.The main contents and chapters are as follows:(1)For the requirement of high spatial resolution sensing,the theories and modification technology based on longitudinal microstructured fiber had been studied.The sensing mechanism and interrogation technologies of longitudinal microstructured fiber had been researched through the theories of fiber Bragg grating and scattering enhancement points.Aiming at the requirements of longitudinal microstructured fiber fabrication process,the core modules such as fiber release device,fiber collection device,and stress control device were designed to develop a multi-functional fiber microstructure continuous fabrication platform,which can realize continuous fabrication along the fiber axis and flexible control in space for uniform and non-uniform fiber grating,microcavity structure and local scattering enhancement points etc.The movement speed of the optical fiber can be precisely controlled with the range of 6 mm/min ～ 10000 mm/min,and the fabrication accuracy of microstructure is 5 μm.This platform can realize automatic manufacturing amd support the fabrication of ultra-long microstructured fiber up to 50 km.(2)According to the requirement of ultra-high spatial resolution distributed sensing in short-range,the continuous microstructured fiber grating were proposed and researched as well as its sensing technology.The continuous microstructured fiber grating was designed by layer peeling algorithm and group delay control method to separate the wavelength channels,and a 21-channel grating was fabricated by the seamless ultra-violet writing technology.The temperature characteristics of the grating were studied,and the demodulation method based on waveform tracking was proposed for temperature sensing.The uniform temperature field,gradient temperature field and radiation temperature field were studied experimentally,achieving a 3mm spatial resolution and 63 mm range real-time temperature field monitoring with the maximum temperature gradient of 7.85℃/mm.(3)In order to meet the requriment of large capacity with high spatial resolution,a distributed optical fiber sensing technology was proposed based on weak reflection FP microstructured fiber.The weak reflection FP microstructure with wavelength and frequency encoding capacity was designed as well as its multiplexing scheme,achieving the multiplexing capacity of 243 in a single fiber under the condition of 10 mm spatial resolution.The detection range was up to 2430 mm,which was an order of magnitude higher than the one-dimensional wavelength coding technology.Further,for the requirement of high sensitivity pressure detection in gastrointestinal motility monitoring,the soft polymer package method was utilized to enhance the sensitivity of lateral pressure.The theoretical model was established and the finite element method was used to analyze the key parameters of package such as elastic modulus,Poisson’s ratio and diameter.The pressure sensitivity of the sensing fiber was enhanced 700 times than the bare fiber.A sensing demodulation system based on tunable FP filter and spectrum Fourier transform method was developed for the static and dynamic pressure response experiments,achieving 120cm/min dynamic pressure wave detection with a 10 mm spatial resolution,2.2 MPa/nm pressure sensitivity,0.46 k Pa pressure resolution,and0～40 k Pa pressure sensing range.(4)In order to meet the requirement of ultra-long sensing distance with high spatial resolution,the scattering enhanced microstructured fiber was proposed as well as its distributed sensing technology.The local defects were introduced in single-mode fiber core to build up equidistant scattering enhancement points with increasing strength along the fiber,and the sensing distance can reach 90.5km by segmented regulation method.A 17 km backscattering enhanced microstructed fiber was fabricated through single-pulse laser exposure,which enhanced the backscattering signal around 5d B.A high-resolution distributed liquid level sensing technology based on scattering enhanced microstructured fiber was proposed for the demands of large dynamic range and high-precision liquid level monitoring in the fields of petroleum transportation and storage,wastewater treatment,etc.A large-scale liquid level monitoring technology was proposed based on the temperature mutation effect of the gas phase and the liquid phase on the gas-liquid contact surface,and the sensitivity and spatial resolution of the liquid level measurement were further improved through the winding package.Combined with coherent phase demodulation technology,the dynamic liquid level measurement was realized with the spatial resolution of 74μm experimentally.Based on the17 km microstructured fiber,the liquid level measurement range could reach up to 85 m.更多还原