TFBG的Fabry-Perot干涉型纵向微位移传感研究

提出了一种利用光纤Fabry-Perot(F-P)干涉结构的微位移传感器,该F-P干涉结构是由双倾斜光纤光栅(tilted fiber Bragg grating,TFBG)沿轴向错开一定距离构成空气腔形成的.入射光经双TFBG及其高反射端面往返传播,从而构成F-P干涉结构.光纤沿纵(z轴)向移动时,F-P腔的腔长发生变化,致使干涉光谱的自由光谱范围随之产生变化.实验验证,该传感器在0~115μm的测量范围内获得了高达0.475nm/μm的灵敏度,较之前提出的光纤光栅型传感器灵敏度提高了近3倍.     

非本征光纤法珀传感器的振动特性研究

针对光纤法珀(Fabry-Perot, FP)超声波传感器振动特性,将传感器薄板振动简化为具有集中参数的二阶振动,推导二阶振动方程的集中参数(力阻抗、等效质量、弹性系数、集中力),获得传感器共振频率、振幅灵敏度与结构参数设计关系。测试直径2.52 mm、厚度150 μm玻璃振动薄板在空气、水中的共振频率分别为205 kHz及115 kHz,水介质中共振频率振幅灵敏度约18 pm/Pa。制作的传感器可测试局放产生超声波的最小声压约1 Pa。     

Interrogation of extrinsic Fabry-Perot interferometric sensors using arrayed waveguide grating devices

In this paper, we present details of a solid state interrogation system based on a 16-channel arrayed waveguide grating (AWG) for interrogation of extrinsic Fabry-Perot interferometric sensors. The sensing element is configured in a reflecting mode and is illuminated by a broad-band light source through an optical fiber. The spectrum of light reflected from the sensor is analyzed using an AWG device acting as a coarse spectrometer. Using measurement points from the AWG channels, the original spectrum of the sensing element is reconstructed by a means of curve fitting. This allows sufficient information for the position of the reflection peak (or inverted peak) to be uniquely determined and the value of a measurement quantity obtained. In addition to the theoretical simulations of the proposed measurement system, we provide details of the laboratory evaluation.     

Vernier-effect optical interrogation technique for fiber Bragg grating sensors

This work demonstrates a new technique for real-time optical sensor interrogation by exploiting a novel Vernier effect between the multiple (comb) wavelength responses of a multiplexed fiber Bragg grating array and the fixed discrete wavelengths of an all-solid-state tunable laser. Sets of output photodetector voltages serve as high-resolution optical "signatures" to determine uniquely the strain in the single fiber section. The sensor demonstrated here is compact, lightweight, and is specifically intended for remote operability in harsh (vibrational) environments. In this proof of concept, strain values over a range of nearly 500 microepsilon can be easily resolved to better than 5.9 microepsilon, which is the incremental limit of the mechanical test fixture used to induce strain in the experiment.     

光纤法-珀传感器并联复用的互相关解调

为了实现光纤法-珀传感器并联复用信号的高精度、绝对腔长解调,提出了一种改进的互相关解调法。该方法采用了特殊的相关因子,使得它与复用输出信号的互相关函数在传感器各腔长处为单峰从而有利于腔长比较接近的传感器的分辨;采用分段黄金搜索法减少了计算量,解调速度快。在宽带光源、光谱仪等组成的解调系统中对两只传感器复用进行了实验验证,结果表明:该系统可以实现光纤法-珀传感器并联复用信号的解调,能分辨的传感器之间的最小腔长差小于6ìm,腔长波动小于0.07ìm。     

光纤非本征法布里-玻罗传感器兰姆波检测灵敏度分析

基于兰姆波的结构工况检测技术在评估复合材料和金属结构的安全性和耐久性方面发挥着重要的作用。作为对传统的压电换能器（PZT）的一种很好的替代,光纤传感器在传感方面的应用正被广泛地挖掘出来,包括兰姆波检测。本文从理论上建立了超声兰姆波作用下光纤非本征法布里．玻罗（EFPI）传感器参数与其输出性能之间的关系。数值结果显示了传感器的性能与其相对于声源的方向角以及传感器的计量长度与超声波长的比值相关。所得出的结论对于EFPI传感器精确地探测兰姆波提供了理论依据。     

Instrumentation design for bridge scour monitoring using fiber Bragg grating sensors

Scour is one of the main causes of bridge failures. In order to measure and monitor scour depth variations including deposition (refilling) process, three designs for a scour monitoring system using fiber Bragg grating (FBG) sensors are discussed in the present study. By a comparative study, one of them is recommended in the present study and its instrumentation manufacture process is also introduced in detail. Using this recommended design, the advantages of FBG sensors for monitoring, such as immunity from electromagnetic interference and multiplexing capability, can be fully utilized. Both scour depth variations and entire scour development process including deposition process can be correctly monitored in real-time by continuously identifying the locations of emerging FBG sensors from the riverbed. A reliable sensor protection measure is also designed for FBG sensors in harsh environments, especially in floods. Finally, a verification test using a flume is carried out in the laboratory and three experimental cases are conducted to demonstrate the capability of FBG sensors and applicability of the recommended scour monitoring system. It can be concluded that the recommended scour monitoring system using FBG sensors is capable of measuring the water level, (maximum) scour depth, entire process of scour development, and deposition height due to refilling process. The advantages over other conventional scour monitoring systems are clearly demonstrated.     

Mechanical characterization of bone cement using fiber Bragg grating sensors

The aim of this work was the study and understanding of the behavior and linearity of an optical fiber Bragg grating (FBG) sensor embedded in bone cement. Test its ability to monitor strains inside bone cement during different mechanical tests, at real-time. Bone cement is a biomaterials based on polymethacrylate used as fixation method in artificial joints. Work as a bonding, load transfer and optimal stress/strain distribution inside the complex human body environment. Bone cement is the weakest element in a joint implant, being considered the main reason of prosthesis loosening.Inside the bone cement, its temperature, longitudinal strain and load were measured using fiber Bragg gratings. All the measurements report a linear response showing a good adaptation and optimization of the load transfer between the biomaterial and the embedded optical sensor.     

Performance evaluation of metal-coated fiber Bragg grating sensors for sensing cryogenic temperature

A metal recoated fiber Bragg grating sensor has been designed, fabricated and tested to study its temperature response at cryogenic temperature around 15 K. Metals like aluminium (Al), copper (Cu), lead (Pb) and indium (In) are considered for recoating the FBG sensors. Indium recoated FBG (IRCFBG) sensors showed a higher sensitivity at around 15 K compared to Al, Cu and Pb coated FBG sensors. In addition, the IRCFBG sensor was tested for its repeatability, stability and performance in the high magnetic field (8 T). The experimental results of the IRCFBG sensor test revealed a satisfactory performance. They will be reported in this paper.     

Fiber-optic Fabry-Perot sensors based on a combination of spatial-frequency division multiplexing and wavelength division multiplexing formed by chirped fiber Bragg grating pairs

Effective multiplexing for a very large number of fiber-optic fiber-Bragg-grating-based Fabry-Perot (FBGFP) sensors is proposed that is based on wavelength division multiplexing (WDM) and spatial-frequency division multiplexing (SFDM). For WDM, FBGFP sensors are arranged in different wavelength domains formed by a series of chirped fiber Bragg gratings with different central wavelengths while the sensors with different cavity lengths within the same wavelength domain are multiplexed by use of SFDM because they have different spatial frequencies as a result of their different cavity lengths. In principle, a thousand FBGFP sensors could be multiplexed with such an approach. The experimental results show that a strain accuracy of better than +/-10 microepsilon has been achieved with little cross talk.     

Optical scanning extrinsic Fabry-Perot interferometer for absolute microdisplacement measurement

We report an optical-scanning, dual-fiber, extrinsic Fabry-Perot interferometer system for absolute measurement of microdisplacement. The system involves two air-gapped Fabry-Perot cavities, formed by fiber end faces, functioning as sensing and reference elements. Taking the scanning wavelength as an interconverter to compare the gap length of the sensing head with the reference-cavity length yields the absolute measurement of the sensing-cavity length. The measurement is independent of the wavelength-scanning accuracy, and the reference-cavity length can be self-calibrated simply by one's changing the sensing-head length by an accurate value.     

Simultaneous strain and temperature measurement using a compact photonic crystal fiber inter-modal interferometer and a fiber Bragg grating

An all-fiber sensor scheme for simultaneous strain and temperature measurement is presented. The sensing head is formed by serially connecting a polarization maintaining photonic-crystal-fiber-based inter-modal interferometer (IMI) with a fiber Bragg grating (FBG). The IMI, exhibiting an opposite strain response as compared to that of the FBG, is highly sensitive to strain, while it is insensitive to temperature. This has potential for improving the strain and temperature measurement resolutions. A sensor resolution of ±8.3 με in strain and ±2 °C in temperature are experimentally achieved within a strain range of 0-957.6 με and a temperature range of 24 °C-64 °C, respectively.     

High-resolution interrogation technique for fiber optic extrinsic Fabry-Perot interferometric sensors by the peak-to-peak method

An improved peak-to-peak method is developed for interrogating the absolute cavity length of fiber optic extrinsic Fabry-Perot interferometric (EFPI) sensors with high resolution. A fiber Fabry-Perot tunable filter (FFP-TF) is used to scan the optical spectrum of an EFPI, and the problems caused by the nonlinear performance and poor repeatability of the FFP-TF are removed by using a wavelength calibration technique. A linear fitting is used to calculate the wavelength spacing between two adjacent apexes in the optical spectrum, and the cavity length can be retrieved using this wavelength spacing. The experimental results show that the measuring resolution is improved from 25 to 1 microm, and a linear output is also obtained.     

基于光纤光栅传感器的结构故障定位方法

提出了一种实现结构故障定位和故障实时监测的新方法.该方法利用光纤光栅传感网络测量结构应变,得到结构的挠度矩阵,分析故障前后挠度矩阵变化,计算得出故障定位向量,进而确定损伤区域,实现了结构故障准确定位和健康状况实时监测.实验结果表明,上述方法大大提高了故障定位的准确度和实时性.     

Modeling and analysis of an extrinsic Fabry-Perot interferometer cavity

A schematic representation of optical feedback between two resonator mirrors undergoing a phase shift each round trip as a function of the separation of the mirrors is studied. A transfer function modeling of the extrinsic Fabry-Perot interferometer (EFPI) is presented. Nyquist analysis has been used to forecast the operational stability and possibility of interference in an EFPI. The analysis with two perfectly parallel surfaces of the cavity shows efficient interference. The performance when there is some tilt between the two mirrors in the cavity is also studied and is presented. In this case some restricted interference is found.     

人体测温光纤光栅温度传感器的研制

针对医疗行业对人体测温的需要,研制了一种以裸光纤Bragg光栅为传感元件的光纤光栅温度传感器,并对其温度特性进行了研究.采用恒温水浴对工作波长为1 557 nm和1 547 nm附近的2只光纤光栅传感器进行温度定标.结果表明,在34～48℃范围内,光纤光栅的中心波长随温度的变化呈现良好的线性关系,相关系数分别为0.998 3和0.997 4,光纤光栅温度传感器的测温标准偏差分别为0.239℃和0.245℃,可应用于医疗中人体温度的实时监测.     

抛弃式光纤温深仪系统设计与实现

海水温度梯度是海洋调查、海洋研究的重要参数,抛弃式温度剖面测量系统(Expendable Bathy Thermograph,XBT)是一种可在测量船走航状态下进行海洋温度剖面测量的仪器,具有实时、快速和低成本的特点.传统XBT通常不使用深度传感器,而是根据探头入水时间利用经验公式推算所处深度,深度误差较大.文章介绍了...     

Application of chirped fiber Bragg grating sensors for identification of crack locations in composites

Chirped fiber Bragg grating (FBG) sensors were applied for the identification of crack locations in carbon fiber reinforced plastic (CFRP) laminates since the reflection spectrum from a chirped FBG was expressed as a function of the position along the grating. For the crack identification in the 90° ply of a cross-ply laminate, a chirped FBG sensor, whose grating length and spectrum width were 50 mm and about 5 nm respectively, was embedded into the 0° ply of the CFRP cross-ply laminate, and the reflection spectra were measured after tensile loadings were applied to the laminate. As a result, the spectra had dips corresponding to locations of transverse cracks. This change in the form of the spectrum was also confirmed by a theoretical calculation. Hence, the crack locations could be identified from the form of the spectrum. Furthermore, it was demonstrated that a small-diameter chirped FBG sensor could also be applied for the identification of the crack locations.     

Method for determination of crack bridging parameters using long optical fiber Bragg grating sensors

The state of the local fiber–matrix interface highly influences the propagation of cracks in fiber-reinforced composites and thus the stress distribution in any bridging fiber. This paper demonstrates that by embedding a long optical fiber Bragg grating into a reinforcing fiber and using an established model of the grating response to non-uniform stress distributions, one can determine key parameters of a crack bridging model. The grating extending into the epoxy on each side of the crack is subject to a strain function as a result of all micro-mechanical phenomena acting along the fiber. Furthermore, this technique does not require that one knows a priori the exact location of the crack. Two types of central crack specimens with an artificial crack were fabricated and tested, one with a strong interface and one with a weaker interface resulting in frictional sliding. The results demonstrate that this technique is efficient for the measurement of the bridging forces through validation by previous measurements using short Bragg gratings and the deduction of interface parameters. Analysis also shows that the sensitivity of the Bragg grating sensor to the bridging force is sufficient, even for the more realistic case of an initially zero-width crack e.g. grown by fatigue.