分布式光纤拉曼温度传感器的对称解调

提出了一种用于分布式光纤拉曼温度传感器的对称解调新方案,采用瑞利散射光时域反射仪(OTDR)曲线解调光纤的反斯托克斯散射光时域反射仪曲线。首先将测量温度范围分成数段,用传统解调方法获取待测温度,然后判断该温度属于哪段内,最后用该对称的数段边界标定温度解调得到偶数个温度测量值,取平均值作为测量值。该方法提高了系统的测温精度和稳定性,系统的测温误差在±0．05℃内,空间分辨力1 m。实验结果与理论分析一致。     

带光放大器的分布式光纤拉曼温度系统

 详细阐述了红外双波长带光放大器的分布式光纤拉曼温度系统原理,为了抑制放大器的自发辐射增长、温漂噪声积累、瑞利背向散射光窜扰反斯托克斯背向散射光,采用两条已知温度的曲线和最近测量温度曲线的解调方法,提高了系统的测温精度和稳定性并降低了系统的成本。实验结果与理论分析一致,系统的测温误差在±0.1 ℃内。     

分布式光纤喇曼温度传感器的循环解调法

为了抑制温漂噪声积累,瑞利背向散射光窜扰反斯托克斯背向散射光,考虑了最近测量瑞利背散射光曲线解调反斯托克斯背向散射光温度曲线方法,即循环解调方法;该方法提高了系统的测温精度、稳定性,降低了系统的成本.实验结果与理论分析一致,系统的测温精度达±0.05℃.     

基于单模光纤的分布式温度传感器研制

在对光纤背向喇曼散射温度效应理论分析的基础上,研制了基于单模光纤的5km分布式温度传感器。实验比较了温度传感解调方法,选择反斯托克斯(Anti-Stokes)和斯托克斯(Stokes)背向喇曼散射光强度比值进行解调。介绍了系统的硬件组成和软件实现。实验表明,系统能精确地进行分布式测温,温度分辨率为1℃,空间分辨率为2m。     

基于拉曼散射光动态校准的分布式光纤温度传感系统

分布式光纤温度传感(distributed temperature sensor, DTS)系统进行温度测量时,参考光斯托克斯光强度随着温度的升高而增大,使信号光反斯托克斯光与参考光斯托克斯光强度的比值减小,测量温度小于真实温度,降低系统的测温准确度.本文提出并实验验证了一种新的动态校准法修正斯托克斯光信号,可有效减小斯托克斯光导致的测温误差,提高系统的测温准确度.该方法根据参考光纤中的实时斯托克斯光强分布,模拟出对应的整条光纤在参考温度环境中的斯托克斯光强度曲线,实现斯托克斯光的温度响应修正.实验结果表明,与传统温度解调方法相比,分布式光纤温度传感系统进行斯托克斯光动态校准后测温准确度最高提升4.3℃.与瑞利噪声抑制法联用后,测温准确度提高8.9℃.本研究为DTS系统进行高温环境温度监测提供了一种新的解决方案.     

在单模光纤中放大的反斯托克斯拉曼背向自发散射的温度效应

在单模光纤中,输入的激光功率大于阈值时．出现放大的反斯托克斯拉曼背向自发散射现象。实验发现：放大的反斯托克斯拉曼背向自发散射具有温度效应．与反斯托克斯拉曼背向自发散射一样,放大的拉曼散射光的光子通量受到光纤温度的调制。反斯托克斯拉曼背向白发散射的放大效应抑制了单模光纤中的相干噪声,改善了系统的信噪比。实验还发现．放大的反斯托克斯扎曼背向自发散射空域曲线上放大的端点位置随激发功率的增高前移并具有一定的规律性。放大的反斯托克斯拉曼背向自发散射的温度效应作为一种新的测温原理,已应用于远程30km分布光纤温度传感器系统。     

基于拟合衰减差自补偿的分布式光纤温度传感器

针对斯托克斯光和反斯托克斯光的本质损耗、附加损耗使分布式光纤温度传感器产生测温误差的问题,通过对分布式光纤温度传感器的温度解调原理的研究,提出了拟合斯托克斯光与反斯托克斯光之间衰减差的方法实现温度自补偿,以此减小测温误差.以传感光纤上不同位置的两部分作为参考段和测温段,参考段的光信号作为测温段拟合多阶衰减差和解调温度的参量,通过引入多阶拟合结果解调温度,减小因斯托克斯光和反斯托克斯光的本质损耗、附加损耗导致的温度误差,实现温度的初步修正.改变光纤上同一位置的温度,取3组不同温度值及对应信号值计算引入拟合衰减差前后的瑞利噪声,分析了瑞利噪声与光纤长度和温度的关系,通过引入拟合衰减差消除瑞利噪声,减小了斯托克斯光和反斯托克斯光的本质损耗、附加损耗导致的瑞利噪声误差,实现温度的再次修正.分析比较多阶衰减差拟合结果对测温误差以及消除瑞利噪声的影响,获得最优拟合阶次.在拟合因参考段的附加损耗而导致的测温段的附加误差后,通过拟合结果进行温度补偿,完成了最终温度修正.实验结果表明,在30-90℃,引入一阶线性拟合结果的温度修正效果最好,经过三次修正后,测温误差从10.50℃降低至0.90℃.     

基于累加平均的分布式光纤拉曼测温系统

分布式光纤拉曼温度传感(DTS)系统是一套基于光纤中的拉曼散射效应来实现分布式温度监控的系统,利用光纤中拉曼散射光的强度与光纤的温度状态有关的原理对温度进行实时监测。设计了一套9 km的光纤拉曼测温系统,利用数据采集卡对斯托克斯和反斯托克斯光进行采集,在电脑端对温度进行累加平均处理,将微弱的信号从系统的噪声中提取出来,提高其信噪比。在累加平均16 000次的情况下测温精度达到了±2℃。     

光纤背向激光自发喇曼散射的温度效应研究

从理论和实验上研究了光纤背向激光自发喇曼散射的温度效应.光纤背向激光自发反斯托克斯喇曼散射、斯托克斯喇曼散射光的相对强度正比于光纤分子上、下能级粒子数的布居,依赖于温度.由于实际系统中,作为分光用的干涉滤光片不可能完全隔离背向瑞利散射光,因此,实际系统温度曲线比理论曲线低,本文给出了理论修正公式,提出了附加修正项,它与隔离度和波长有关.     

分布式光纤拉曼测温系统中解调算法的优化

针对分布式光纤拉曼测温系统传统的温度解调算法进行了优化,提出了补偿光纤色散以及光纤损耗两种算法。通过重合处理补偿因反斯托克斯光与斯托克斯光信号的衰减速度不同而造成的温度解调误差;通过色散补偿算法对斯托克斯散射信号的位置进行修正,弥补因两束光的传播速度不同造成的测量误差,提高了系统的测温精度和定位精度。     

基于环结构的新型分布式光纤振动传感系统

提出并验证了一种新颖的基于环形马赫-泽德干涉仪结构的全分布式光纤振动传感系统.采用直流光实时动态定位技术，通过在干涉仪光路中引入环结构，将直线型干涉仪转化为环型回路，使得一个马赫-泽德干涉仪中相向传输两路光波，相当于构成双马赫-泽德干涉仪.当振动信号作用于传感光纤时，相向传输的两路直流光同时产生相同的相位信号并沿不同的路径传输至光接收单元，采用数字信号处理技术分析接收信号即可实时获得振动的空间位置和频率、幅度等特性参数.实验中成功实现了监测距离为1.01km的分布式振动传感，单点振动的空间分辨率小于40m.另外，从理论上分析并模拟了系统对多点同时振动进行检测和定位的可行性.     

Creep deformation measurement using quartz optical fiber

This paper describes an optical system for high temperature creep strain measurement using quartz optical fiber, super long working distance microscope and digital image processing techniques. In this system one end of the quartz optical fibers is arrayed in a small area on the specimen surface and the other end is illuminated by a laser beam. The fiber ends on the specimen surface form the spot array. The small optical spots on the specimen are tracked by a CCD camera and the images are processed by digital image processing software. The diameter of each quartz fiber is 100 μm and the fibers can be arrayed in a small area. The local strains are determined by measuring the variety of relative distance between two spots. Experimental results of local creep strain on the welding joints of 15CrMo and HK40 at 850°C are obtained.     

布里渊动态光栅原理及其在光纤传感中的应用

自从2007年布里渊动态光栅被首次提出用于实现光存储以来,该技术得到了国际上的广泛关注和研究.布里渊动态光栅本质上是由相干声波场激发的折射率光栅,一般情况下两束抽运光(频率差等于光纤的布里渊频移)以相同的偏振态从光纤两端注入到光纤中,通过受激布里渊散射效应激发出相干声波场,即形成布里渊动态光栅.光纤布里渊动态光栅因具有全光产生、参数灵活可控的优点,已被广泛研究应用于光纤传感、光纤特性表征、光存储、全光信号处理、微波光子学和高精度光谱分析等.本文分析布里渊动态光栅产生和探测原理,重点探讨在高性能分布式光纤传感上的应用,这些应用包括高灵敏度温度和应变分布式传感、温度和应变同时解调、分布式横向压力传感、分布式静压力(气压或液压)传感、高空间分辨率分布式传感和高精度光谱分析.     

Dual-source distributed optical fiber sensor for simultaneous temperature and strain measurements

A dual-source distributed optical fiber sensor system with combined Raman and Brillouin scatterings is designed for simultaneous temperature and strain measurements. The optimal Raman and Brillouin signals can be separately obtained by adjusting the powers of the two sources using an optical switch. The temperature and strain can be determined by processing the optimal Raman and Brillouin signals. The experimental result shows that 1.7 ?C temperature resolution and 60-με strain resolution can be achieved at a 24.7-km distance.     

Design of an optical fiber sensor for linear thermal expansion measurement

Design and operation of an optical fiber device for temperature sensing and thermal expansion measurement are reported. The modulated intensity has been measured by using a pair of 450 μm core fiber, one acting as the source and the other one as receiving fiber. In this design, the light intensity modulation is based on the relative motion of the optical fibers and a reflective coated lens. By using displacement calibration data for this sensor, the linear thermal expansion of the aluminum rod is determined. This sensor shows an average sensitivity of about 11.3 mV/°C for temperature detection and 7 μm/°C for thermal expansion detection. Device resolution for a linear expansion measurement is about 3 μm for a dynamic range of 600 μm corresponding to a temperature change of 100°C. The measured linear expansion results are checked against the expected theoretical ones and an agreement within ±2 μm is noticed. The operation of this sensor was also compared with other types and some advantages are observed, which verify the capability of this design for such precise measurements.     

高灵敏度光纤温度传感器

针对深井温度变化小,提出了一种可用于深井温度测量的高灵敏度光纤温度传感器。两根陶瓷插芯从铝管的两端插入构成外腔式光纤法珀干涉仪(EFPI)结构,用螺钉固定插芯,再用高强度的环氧树脂密封该结构,达到防水防尘效果。金属铝和陶瓷插芯具有不同的热膨胀系数,温度的变化将引起EFPI腔长变化,采用高灵敏度光纤白光干涉测量技术,就可以通过测量EFPI腔长获得被测温度。分别在固定温度和不同温度下,对腔长为146.5μm的EFPI光纤温度传感器进行了连续测量。测量结果表明,高灵敏度EFPI光纤温度传感器的腔长-温度灵敏度为260nm/℃,温度测量分辨率为0.002℃。     

Real-time positioning technology of train based on optical fiber coherent Rayleigh backscattering北大核心CSCD

With the rapid growth of railway mileage in China, the degree of heavy load of railway wagons continues to increase. An interference technology based on Rayleigh backscattering signal in optical fiber was proposed by using existing communication optical cables along railway lines. When the fiber vibrated slightly, the phase and refractive index of the fiber at disturbed position changed, which resulting in the Rayleigh backscattering light. By performing differential calculation on the Rayleigh signal curves before and after the operation, the location of the interference light intensity signal corresponded to the location of the disturbances was obtained. Based on this method, the recognition and positioning of railway vehicles were realized. By collecting and analyzing the time-domain and frequency-domain signal, the signal strength, train length, the number of carriages and other characteristics were extracted, and the model of railway vehicles were accurately recognized. Compared with traditional positioning technologies, this technology could realize long-distance monitoring, and the sensing fiber was buried underground on both sides of the railway, which was conducive to the concealment and protection of optical fiber. Experimental results show that the positioning error of the system is within ±10 m, and the detection of railway speed and position within 25 km can be realized. © 2022 Editorial office of Journal of Applied Optics. All rights reserved.