Design of Demodulation System of Interferometric Sensor Based on Labview

For the modified demodulation arithmetic of 3×3 coupler, the processing software built on the basis of Labview is able to demodulate asymmetric 3×3 coupler signal and do further spectrum analysis. It shows that the measured frequency ranges from 10 Hz to 1 000 Hz and phase range is covered by -10 rad^10 rad. The phase sensitivity is 0.5 V/rad. This system is proved to show high resolution and wide dynamic range.

Combined optical fiber interferometric sensors for the detection of acoustic emission

A type of combined optical fiber interferometric acoustic emission sensor is proposed. The sensor can be independent on the laser source and make light interference by matching the lengths of two arms,so it can be used to monitor the health of large structure. Theoretical analyses indicate that the system can be equivalent to the Michelson interferometer with two optical fiber loop reflectors,and its sensitivity has been remarkably increased because of the decrease of the losses of light energy. PZT is powered by DC regulator to control the operating point of the system,so the system can accurately detect feeble vibration which is generated by ultrasonic waves propagating on the surface of solid. The amplitude and the frequency of feeble vibration signal are obtained by detecting the output light intensity of interferometer and using Fourier transform technique. The results indicate that the system can be used to detect the acoustic emission signals by the frequency characteristics.

Accurate Analysis of Multi-Mode Interferometric Optical Fiber Sensor

In view of the problem that the sensing characteristics of the multi-mode interferometric fiber sensors cannot be accurately analyzed,an analysis method based on the fast Fourier transform(FFT)and inverse fast Fourier transform(IFFT)is proposed and demonstrated theoretically and experimentally.The suitabilities of the rectangular window function with the narrow main lobe(high spectrum resolution)and low side lobe(high main mode energy leakage)and the Hanning window function with the wide main lobe(low spectrum resolution)and high side lobe(high energy concentration)in this kind of sensor analysis are discussed,respectively.This method can not only realize the sensing performance analysis of the various modes,but also overcome the inconsistency of the different interference wavelength(dip)sensing characteristics in the conventional analysis methods.At the same time,this method is also beneficial to solve the repetitive problem of such sensors.

Study on Refraction Index Sensors Using Fiber Grating F-P Cavity

In this paper, the reflective spectra of a refraction index sensor were analyzed based on fiber grating F-P cavity. The sensor was constituted by two identical fiber gratings. Compared with the refraction index sensor using one fiber grating, the fiber grating F-P cavity sensor has narrower resonant peak and it can be used for more accurate measurement. The resonant peaks in the reflective spectra of the sensor are changed with small changes of the refraction index of the measured chemical liquids or cell samples. So it has potential applications in biology and chemistry.

用于检测痕量铅离子的功能化反射结构光纤干涉传感器

铅离子(Pb^(2+))是日常生活中常接触的有毒重金属污染物之一。本研究开发了一种新型反射式光纤干涉传感器,用于检测痕量铅离子。该传感器结构由单模光纤、无芯光纤和细芯光纤(TCF)依次拼接而成。TCF的包层被氢氟酸部分腐蚀并涂覆功能化的水凝胶传感膜。该传感膜选用甲基丙烯酸2-羟基乙酯(2-HEMA)作为识别单体。2-HEMA中的氧原子能与Pb^(2+)发生配体-受体相互作用,形成“-O-Pb-O-”交联结构,从而改变TCF的新包层有效折射率。因此,可以通过观察反射光谱中光信号的变化来检测水溶液中Pb^(2+)的浓度。所提出的传感器具有很高的检测灵敏度(1.926×10^(9)nm·mol^(-1)·L),其检测极限为4.14 ppt(1 ng·L^(-1)=1 ppt),比世界卫生组织(WHO)规定的饮用水中Pb^(2+)(10 ppb,1μg·L^(-1)=1 ppb)浓度低1000倍。此外,利用一个方程组实现了该传感器的温度自校准功能,成功地消除了环境温度的干扰。由于该传感器良好的特异性、稳定性以及反射式结构,非常便于实时远程检测,为环境和人类健康监测提供了广阔的前景。

F-P腔光纤传感器研究

文章综述了作者研究组关于F-P腔光纤干涉型传感器多参数测量的研究进展.在单模光纤与薄膜或空气间隙等构成的法布里-珀罗腔结构基础上,分别提出基于F-P腔干涉和基于F-P腔调制菲涅尔反射的温度、液体和固体折射率光纤传感器.理论分析和实验均证明,温度的变化可转化为干涉光谱波峰或波谷中心波长的偏移测量,通过干涉光谱的条纹反衬度可解调出液体或固体折射率.光纤干涉型传感技术可拓展其它功能,是高端领域传感测量的发展方向.

DEVELOPMENT OF EXTRINSIC FABRY PEROT FIBER SENSOR AND ITS APPLICATION TO SMART MATERIALS

In the work of developing extrinsic fabry perot interferometric (EFPI), the key technology of polishing fiber optic endfaces and coating the multilayer of dielectric films on them is raised and resolved to settle the disturbance and stability problem of EFPI, which simplifies the sensing system, improves the sensor performance and reduces the cost. In this paper, the relations between the output interferential light intensity and the F P cavity length are calculated based on the theory of mode field coupling. The EFPI fiber optic sensor is adhered to a distributed smart laminate beam to detect vibration frequency and axial strain value, the results coincident with the results tested by PZT.

Research on stress characteristics of Fabry-Perot sensor with center microbubble structure

The optical fiber based on silicon materials has a smaller thermal expansion coefficient, therefore it can be used for the preparation of sensor devices which are insensitive to temperature but sensitive to refractive index, strain, stress, etc. For example, we can use optical fiber Fabry-Perot （F-P） sensor to achieve high sensitivity stress sensing. In this paper, we design an optical fiber F-P sensor with low cost and high sensitivity based on chemical etching method and analyze the stress sensing properties. Hydrofluoric acid is used to prepare the end face concave hole of the optical fiber first, and then the hollow struc-ture of the fiber F-P sensor is obtained by melting and discharge. This preparation method contributes greatly to enhancing the stress sensing properties and temperature insensitivity of the optical fiber device. The experimental results show that interference spectrum peak change is proportional to the stress change of optical fiber F-P sensor, stress sensitivity can reach 5. 2, and the cost is relatively low. Based on this,it has a certain application value in the stress sensing field.

同轴电缆F-P干涉传感器分布式应变测量

针对结构安全监测领域中局部大应变的分布式、全历程监测难题,搭建了基于同轴电缆法布里-珀罗干涉传感器的分布式应变测量系统。首先介绍了同轴电缆法布里-珀罗干涉传感器的应变感知原理。然后提出了测量系统的架构和功能实现方法,其分布式应变测量功能通过基于虚拟仪器技术的自动测量程序实现。最后进行了若干性能实验,分别验证了该测量系统的稳定性、应变测量误差、应变分辨率及其分布式应变测量效果。实验结果表明:该测量系统的谐振频点识别精度为21. 8×10-6,应变测量相对误差在7%以内,应变分辨率为40με。该测量系统可满足结构大应变的分布式、全历程监测需求。

Influences of semiconductor laser on fibre-optic distributed disturbance sensor based on Mach-Zehnder interferometer

This paper investigates the influences of a semiconductor laser with narrow linewidth on a fibre-optic distributed disturbance sensor based on Mach-Zehnder interferometer. It establishes an effective numerical model to describe the noises and linewidth of a semiconductor laser, taking into account their correlations. Simulation shows that frequency noise has great influences on location errors and their relationship is numerically investigated. Accordingly, there is need to determine the linewidth of the laser less than a threshold and obtain the least location errors. Furthermore, experiments are performed by a sensor prototype using three semiconductor lasers with different linewidths, respectively, with polarization maintaining optical fibres and couplers to eliminate the polarization induced noises and fading. The agreement of simulation with experimental results means that the proposed numerical model can make a comprehensive description of the noise behaviour of a semiconductor laser. The conclusion is useful for choosing a laser source for fibre-optic distributed disturbance sensor to achieve optimized location accuracy. What is more, the proposed numerical model can be widely used for analysing influences of semiconductor lasers on other sensing, communication and optical signal processing systems.

High-sensitivity refractive index sensors based on Fano resonance in a metal-insulator-metal based arc-shaped resonator coupled with a rectangular stub

A metal-insulator-metal(MIM)-based arc-shaped resonator coupled with a rectangular stub(MARS) structure is proposed. This structure can generate two tunable Fano resonances originating from two different mechanisms. The structure has the advantage of being sensitive to the refractive index, and this feature makes it favorable for application in various microsensors. The relationship between the structural parameters and Fano resonance is researched using the finite element method(FEM) based on the software COMSOL Multiphysics 5.4. The simulation reveals that the sensitivity reaches1900 nm/refractive index unit(RIU), and the figure of merit(FOM) is 23.75.

Application of a joint algorithm based on L-T to pulse pressure detection signal of fiber Fabry-Perot nano pressure sensor

An improved denoising method and its application in pulse beat signal denoising are studied.The proposed denoising algorithm takes the advantages of local mean decomposition(LMD)and time-frequency peak filtering(TFPF),called L-T algorithm.As a classical time-frequency filtering method,TFPF can effectively suppress random noise with signal amplitude retained when selecting a longer window length,while the signal amplitude will be seriously attenuated when selecting a shorter window length.In order to maintain effective signal amplitude and suppress random noise,LMD and TFPF are improved.Firstly,the original signal is decomposed into progression-free survival(PFS)by LMD,and then the standard error of mean(SEM)of each product function is calculated to classify many PFSs into useful component,mixed component and noise component.Secondly,by using the shorter window TFPF for useful component and the longer window TFPF for mixed component,noise component is removed and the final signal is obtained after reconstruction.Finally,the proposed algorithm is used for noise reduction of an Fabry-Perot(F-P)pressure sensor.Experimental results show that compared with traditional wavelet,L-T algorithm has better denoising effect on sampled data.

基于EFPI的数字配电网超声检测传感器

针对数字配电网设备存在的局部放电(partial discharge,PD)超声信号检测需求,研究并设计了一种基于非本征型法布里-珀罗干涉(extrinsic Fabry-Perot interferometric,EFPI)的超声波传感器,用于检测PD产生的超声波信号。通过仿真软件COMSOL模拟了不同膜片厚度以及膜片半径的光纤法布里-珀罗(Fabry-Perot,F-P)传感器的灵敏度和固有频率,选择了最佳的结构参数并制作了EFPI传感器。仿真结果表明,传感器的灵敏度可以达到106.6 nm/kPa,固有频率为234.85 kHz。当频率为30 kHz和40 kHz的超声波信号分别加到传感器上时,EFPI超声波传感器检测到的频率分别为29.97 kHz和39.92 kHz。实验结果表明,该传感器可以准确地检测高压模拟罐体中PD产生的超声波信号,且可检测最小放电量为53 pC,具有体积小、频响范围宽、检测灵敏度高的特点,有良好的应用前景。

Reflectometric and interferometric fiber optic sensor's principles and applications

Fiber optic sensors have been widely used and studied in recent times. This paper presents operating principles and applications of fiber optic sensors namely reflectometric and interferometric fiber optic sensors. Majority of optical fiber sensors fall under these two broad categories. Both interferometric and reflectometric fiber optic sensors are becoming popular for their ease of use, flexibility, long distance sensing, and potentially noise free detection. Also, these sensors can easily be used in various applications such as structural health monitoring, perimeter intrusion detection, temperature monitoring, and other numerous applications. This paper broadly classifies fiber optic sensors into two subtypes. The paper further highlights different sensors based on their sensing resolution, range, spatial advantages, and applications.

A new demodulation technique for optical fiber interferometric sensors with[3×3]directional couplers

Optical fiber interferometric sensors based on [3×3] couplers have been used in many fields. A new technique is proposed to demodulate output signals of this kind of sensors. The technique recovers the signal of interest by fitting coefficients of elliptic （Lissajous） curves between each fiber pair. Different from other approaches, this technique eliminates the dependence on the idealization of [3×3] coupler, provides enhanced tolerance to the variance of photoelectric converters, and is anti-polarization in a certain extent. The main algorithm has been successfully demonstrated both by numerical simulation and experimental result.

Asymmetric Fabry-Pérot interferometric cavity for fiber optical sensors

Good linearity and wide dynamic range are the advantages of asymmetric Fabry-Pérot （F-P） interferometric cavity, whose realization has been long for. Based on optical thin film characteristic matrix theory, an asymmetric F-P interferometric cavity with good linearity and wide dynamic range is designed. And by choosing the material of two different thin metallic layers, the asymmetric F-P interferometric cavity is successfully fabricated. The design theory and method of this asymmetric F-P interferometric cavity have been described in detailed. In this paper an asymmetric F-P interferometric cavity used in fiber optical sensor is reported.

干涉型光纤地震检波器研发及效果分析

光纤传感器具有高灵敏度、大带宽、抗电磁干扰能力强等技术优势,光纤地震检波器采集系统是近年来地震勘探领域研发的热点。在研究干涉型光纤检波器基本构成、传感原理及干涉型光纤检波器采集系统构成的基础上,设计和开发了适用于陆地油气勘探的16道光纤检波器采集系统样机。通过现场地震数据采集,对光纤检波器、动圈式检波器和压电式检波器进行了对比测试,并对试验资料进行了处理分析,结果显示,光纤检波器具有更高的灵敏度、更大的带宽和更好的高频响应,有利于提高地震信号采集精度,改善地震勘探效果,为光纤检波器的推广应用提供了科学依据。

20～1250Hz光纤激光加速度传感系统设计

为了实现高灵敏度、宽频响应的光纤型加速度传感器,以光纤激光器作为加速度传感器的传感元件,建立了光纤激光加速度传感系统,并对该系统的传感原理、灵敏度和谐振频率等性能进行了分析和实验。采用竖直式加速度传感器结构,结构中的传感组件主要由质量块和中空的细钢管组成,光纤激光器受预应力作用后粘接在钢管内部,在加速度作用下,钢管产生的应变引起光纤激光器的应变和折射率发生改变,导致光纤激光器的出射波长随之发生改变,然后使用干涉解调技术检测出波长的动态变化,即可获得波长中包含的加速度振幅和频率信息。实验结果表明,在20~1 250 Hz频段内,竖直式光纤激光加速度传感器的灵敏度约为-126.2 d B[参考值1 rad/(μm/s^2)],频响曲线的波动幅度在±1.9 d B范围内,加速度响应动态范围为77.46~170.26 d B[500 Hz频点,参考值1μm/(s^2·Hz1/2)],加速度分辨率优于0.01 m/s^2。

InSAR可检测的最大最小变形梯度的函数模型研究

InSAR干涉图中的相位噪声是相干性和视数的函数.InSAR能检测的地表最大最小形变梯度,除了受到InSAR硬件的限制外,还直接受到InSAR干涉图中噪声强弱的影响.此外,由于多视处理会改变像元的大小,也会引起可检测的最大最小形变梯度显著变化.本文研究了 InSAR可检测的地表最大最小形变梯度与相干性和视数的关系,并建立了视数为1、5和20时(ERS和ENVISAT常采用的多视数)InSAR可检测的最大最小形变梯度的经验函数模型.最后,本文用伊朗Bam地区的Enivsat ASAR数据进行了试验,结果表明该模型能够准确地判别不同视数和相干性情况下地表变形能否被InSAR技术所检测.与Baran只考虑了相干性的模型相比,本文的模型适用范围更广.

InSAR技术在监测形变中的干涉条件分析

针对InSAR技术在形变监测领域中的应用,本文从分析D-InSAR的干涉机理对其约束条件出发,重点研究空间去相关和形变梯度这两个关键指标对形变信息提取的影响.研究针对不同系统参数的传感器来展开,并论证这两个因素对干涉测量的限制.本文的创新性工作主要集中在以下几个方面:(1)分析了各传感器参数下的临界坡度范围,进而确立了SAR传感器监测的无信息区域;(2)证明了在植被覆盖区,相干性分解必须考虑体散射分量,并依此对模型进行了修正;(3)明确了形变梯度与相位梯度的差异以及两者的函数关系,并将入射角引入形变梯度函数模型.(4)通过模拟数据和真实数据比较各传感器在不同条件下形变监测的优缺点,在统计分析的基础上进一步验证结论.本文的研究是对干涉测量条件的进一步补充,对于理解干涉成像机理、完善InSAR数值计算模型(形变梯度模型和相干性分解模型)以及帮助研究人员根据研究区域特征选择合适的InSAR数据具有一定的参考价值.