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.

Utilization of Extrinsic Fabry-Perot Interferometers with Spectral Interferometric Interrogation for Microdisplacement Measurement

The paper presents a number of signal processing approaches for the spectral interferometric interrogation of extrinsic Fabry-Perot interferometers(EFPIs). The analysis of attainable microdisplacement resolution is performed and the analytical equations describing the dependence of resolution on parameters of the interrogation setup are derived. The efficiency of the proposed signal processing approaches and the validity of analytical derivations are supported by experiments. The proposed approaches allow the interrogation of up to four multiplexed sensors with attained resolution between 30 pm and 80 pm, up to three times improvement of microdisplacement resolution of a single sensor by means of using the reference interferometer and noisecompensating approach, and ability to register signals with frequencies up to 1 kHz in the case of 1 Hz spectrum acquisition rate. The proposed approaches can be used for various applications, including biomedical, industrial inspection, and others, amongst the microdisplacement measurement.

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.

Miniaturized Fiber-Optic Fabry-Perot Interferometer for Highly Sensitive Refractive Index Measurement

This paper presents a novel miniaturized fiber-optic Fabry-Peort interferometer （FPI） for highly sensitive refractive index measurement. This device was tested for the refractive indices of various liquids including acetone and ethanol at room temperature. The sensitivity for measurement of refractive index change of ethanol is 1138 nm/RIU at the wavelength of 1550 nm. In addition, the sensor fabrication is simple including only cleaving, splicing, and etching. The signal is stable with high visibility. Therefore, it provides a valuable tool in biological and chemical applications.

Mesa Diaphragm-Based Fabry-Perot Optical MEMS Pressure Sensor

An optical micro electron mechanical system （MEMS） pressure sensor with a mesa membrane is presented. The operating principle of the MEMS pressure sensor is expatiated by the Fabry-Perot （F-P） interference and the relation between deflection and pressure is analyzed. Both the mechanical model of the mesa structure diaphragm and the signal averaging effect is validated by simulation, which declares that the mesa structure diaphragm is superior to the planar one on the parallelism and can reduce the signal averaging effect. Experimental results demonstrate that the mesa structure sensor has a reasonable linearity and sensitivity.

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.

Study on Fiber-Optic Low-Coherence Interferometric and Fiber Bragg Grating Sensors

This article reviews author＇s research work on fiber-optic sensors over the last twenty years. It includes two aspects： low-coherence interferometric sensors （LCI） and fiber Bragg grating （FBG） sensors. For LCI sensors, author＇s work mainly focuses on the interrogation and multiplexing methods for Fizeau and Fabry-Perot interferometric sensors at the University of Kent at Canterbury （UKC）, UK, and study on novel Fabry-Perot interferometric sensors and their multiplexing methods at Chongqing University （CQU） and University of Electronic Science ＆ Technology of China （UESTC）, China, respectively. For FBG sensors, a number of multiplexing schemes are proposed and demonstrated at UKC, and then novel methods for realization of multi-parameter measurement and long-distance measurement based on the FBG sensor and its combination with other optical fiber sensors are also reported at CQU ＆ UESTC. Thus, author＇s study on these two topics can be diviaed into two periods, at UKC and at CQU ＆ UESTC, China. This review is presented in such a time sequence.

Ultrasonic signal detection based on Fabry–Perot cavity sensor

Acoustic/ultrasonic sensors are devices that can convert mechanical energy into electrical signals.The Fabry–Perot cavity is processed on the end face of the double-clad fiber by a two-photon three-dimensional lithography machine.In this study,the outer diameter of the core cladding was 250μm,the diameter of the core was 9μm,and the microcavity sensing unit was only 30μm.It could measure ultrasonic signals with high precision.The characteristics of the proposed ultrasonic sensor were investigated,and its feasibility was proven through experiments.Its design has a small size and can replace a larger ultrasonic detector device for photoacoustic signal detection.The sensor is applicable to the field of biomedical information technology,including medical diagnosis,photoacoustic endoscopy,and photoacoustic imaging.

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.

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。

Pressure Sensor Based on the Fiber-Optic Extrinsic Fabry-Perot Interferometer

Pressure sensors based on fiber-optic extrinsic Fabry-Perot interferometer(EFPI)have been extensively applied in various industrial and biomedical fields.In this paper,some key improvements of EFPI-based pressure sensors such as the controlled thermal bonding technique,diaphragm-based EFPI sensors,and white light interference technology have been reviewed.Recent progress on signal demodulation method and applications of EFPI-based pressure sensors has been introduced.Signal demodulation algorithms based on the cross correlation and mean square error(MSE)estimation have been proposed for retrieving the cavity length of EFPI.Absolute measurement with a resolution of 0.08 nm over large dynamic range has been carried out.For downhole monitoring,an EFPI and a fiber Bragg grating(FBG)cascade multiplexing fiber-optic sensor system has been developed,which can operate in temperature 300℃with a good long-term stability and extremely low temperature cross-sensitivity.Diaphragm-based EFPI pressure sensors have been successfully used for low pressure and acoustic wave detection.Experimental results show that a sensitivity of 31 mV/Pa in the frequency range of 100 Hz to 12.7 kHz for aeroacoustic wave detection has been obtained.

Design of Fiber Magnetic Field Sensor Based on Fiber Bragg Grating Fabry-Perot Cavity Ring-Down Spectroscopy

A novel fiber magnetic sensor based on the fiber Bragg grating Fabry-Perot （FBG-FP） cavity ring-down technique with pulse laser injection is proposed and demonstrated theoretically. A general expression of the intensity of the output electric field is derived, and the effect of the external magnetic field on the ring-down time is discussed. The results show that the output light intensity and the ring-down time of the FBG-FP cavity are in the inverse proportion to the magnitude of the external magnetic field. Our results demonstrate the new concept of the fiber magnetic sensor with the FBG-FP cavity ring-down spectroscopy and the technical feasibility.

High-finesse displacement sensor and a theoretical accelerometer model based on a fiber Fabry-Perot interferometer

A displacement sensor based on the fiber Fabry-Perot (F-P) cavity was proposed in this paper. Theoretical and experimental analyses were presented. Displacement resolution was demonstrated by spectrum-domain experiments to obtain the dynamic range of the F-P sensor, and a piezoelectric crystal unit (PZT) was used as the driver. The output signal was modulated by a piezoelectric ceramic ring and demodulated by a phase-locked oscillator. The experimental results show that the displacement resolution of the F-P sensor is less than 5 nm and the dynamic range is more than 100 μm. As acceleration is the second-order differential of displacement, an accelerometer model was proposed using the finite element method (FEM) nd ANSYS software.

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。

单索面斜拉桥模型钢索载荷应变的光纤传感测量方法

采用光纤应变测量仪对桥梁钢索的应力应变在载荷情况下的变化进行了实验研究 .采用有机玻璃和0 .8mm钢丝 ,设计并制作了单索面斜拉桥模型 .在该桥梁模型上进行了模拟活载的线性加载实验 ,为斜拉桥索力及应力应变的检测提供了一种新测式方法 .

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。

用于干涉型光纤传感器的相位生成载波解调技术

相位生成载波技术是用于光纤传感器中很重要的一种信号解调方法。简要说明了相位生成载波调制的原理和两种基本的调制方法 ,着重介绍了相位生成载波调制信号的解调方法 ,包括 :零差法、伪外差法和合成外差法 ,并对以上各种方法进行了分析比较。对相位生成载波技术在干涉型光纤传感器中的应用作了详细的介绍。针对现在最有希望用于智能结构的光纤布拉格光栅传感器 ,介绍了相位生成载波技术在这方面的应用。

干涉型光纤传感器的消偏振衰落技术研究

本文对消除干涉型光纤传感器信号偏振衰落的偏振分集接收PDR(Polarization Diversity Receiver)技术进行了理论分析.通过三态PDR方式,对输出的最大有效幅度信号进行选取,能够避免传输光偏振态变化导致干涉信号完全衰落的现象,使干涉信号有效幅度在一定范围内变化.采用基于反正切计算的相位生成载波PGC(Phase Generated Carrier)解调技术的相位测量结果不受由于偏振衰落导致干涉信号有效幅度变化的影响.提出结合三态PDR方式和基于反正切计算的PGC解调技术消除偏振衰落问题的影响,实现干涉型光纤传感器中相位信号的理想解调.

干涉型光纤传感器PGC检测中AGC的研究

干涉型光纤传感器解调信号的幅度受多种因素的影响,干涉信号幅度的波动影响最大.自动增益控制(AGC)通过稳定干涉信号幅度来减少解调信号幅度的起伏.峰峰值型AGC虽曾在补偿偏振态的变化给解调信号带来的幅度起伏上起到过作用,但对干涉波形的不同不加区分,反而导致了解调信号的波动,存在原理上的缺陷.该文对此过程进行了深入理论分析,提出了AGC改进方案,构建了改进型AGC电路,并对改进型AGC进行误差分析,其误差比峰峰值型AGC小很多.