Electro-Optical Effect Measurement of Thin-Film Material Using PM Fiber Mach-Zehnder Interferometer

A polarization-maintaining （PM） fiber Mach-Zehnder （MZ） interferometer has been established to measure the EO effect of very thin film materials with optical anisotropy. Unlike a common MZ interferometer, all the components are connected via polarization-maintaining fibers. At the same time, a polarized DFB laser with a maximum power output of 10mW is adopted as the light source to induce a large extinction ratio. Here,we take it to determine the electro-optical coefficients of a very thin superlattice structure with GaAs, KTP, and GaN as comparative samples. The measured EO coefficients show good comparability with the others.

Simulation of distributed optical fiber disturbance detection system based on Sagnac/Mach-Zehnder interferometer and cross-correlation location

A distributed optical fiber disturbance detection system consisted of a Sagnac interferometer and a Mach-Zehnder interferometer is demonstrated. Two interferometers outputs are connected to an electric band-pass filter via a detector respectively. The central frequencies of the two filters are selected adaptively according to the disturbance frequency. The disturbance frequency is obtained by either frequency spectrum of the two interferometers outputs. An alarm is given out only when the Sagnac interferometer output is changed. A disturbance position is determined by calculating a time difference with a cross-correlation method between the filter output connected to the Sagnac interferometer and derivative of the filter output connected to the Mach-Zehnder interferometer. The frequency spectrum, derivative and cross-correlation are obtained by a signal processing system. Theory analysis and simulation results are presented. They show that the system structure and location method are effective, accurate, and immune to environmental variations.

Reflective Ladder Topology Network Based on White Light Fiber-Optic Mach-Zehnder Interferometer

In order to improve the multiplexing capability of the optical sensors based on the lower interferential optic fiber sensing technology and the white light fiber-optic Mach-Zehnder interferometer,reflective ladder topology network ( RLT) with tailored formula was proposed. The topology network consists of 6 rungs sensing elements linked by 5 couplers. Two cases with different choices of couplers were contrasted: one is equal coupling ratio,and the other is tailored coupling ratio. Through the simulation of these two cases,the detailed multiplexing capability was analyzed,and accordingly the experiments were also carried out. The simulation results showed that,the tailored formula enhances the multiplexing capability of the structure. In the first case, the maximum number of sensors which can be multiplexed is 8,and in the other case is 12 fiber optic sensors. The experimental results have a good agreement with numerical simulation results. Thus,it is considered expedient to incorporate RLT into large-scale building,grounds,bridges,dams,tunnels,highways and perimeter security.

Ultrasonic sensitivity-improved fiber-optic Fabry-Perot interferometer using a beam collimator and its application for ultrasonic imaging of seismic physical models

An ultrasonic sensitivity-improved fiber-optic Fabry-Perot interferometer （FPI） is proposed and employed for ultra- sonic imaging of seismic physical models （SPMs）. The FPI comprises a flexible ultra-thin gold film and the end face of a graded-index multimode fiber （MMF）, both of which are enclosed in a ceramic tube. The MMF in a specified length can collimate the diverged light beam and compensate for the light loss inside the air cavity, leading to an increased spectral fringe visibility and thus a steeper spectral slope. By using the spectral sideband filtering technique, the collimated FP1 shows an improved ultrasonic response. Moreover, two-dimensional images of two SPMs are achieved in air by recon- structing the pulse-echo signals through using the time-of-flight approach. The proposed sensor with easy fabrication and compact size can be a good candidate for high-sensitivity and high-precision nondestructive testing of SPMs.

Debonding Patch Detection in FRP-Strengthened Materials with Fiber-Optic Interferometer

The interfacial debonding in fiber-reinforced plastic(FRP)strengthened repair material will affect the bonding strength and lead to failure of the repair without warning.Unfortunately the interfacial damage is normally invisible and often in the form of a patch rather than a through-width crack.Therefore,a debonding patch detection technique based on fiber optic interferometry is proposed.A quasi-impulse loading is applied with a rubberhead hammer and the total elongation of a surface-mounted optical fiber along the length of the repair material is measured as a function of load position.When a debonding patch is present,the induced sudden slope or sign change on the plot of fiber integral strain v.s.load position will reveal the extent and the location of the debonded area.The results of the study indicate that the proposed technique is applicable for debonding patch detection in repaired members under various support conditions.

Measuring Optical Length and Analyzing Accuracy Error Based on All-Fiber Optic Interferometer

An optical length measuring system base on all-fiber optic interferometer is proposed. The theoretical analysis indicates that, when the two branches of the interferometer are equal, the output have the maximum coherent intensity. Therefore, the optical length can be obtained by measuring the distance of collimator movement. Through the experiment and simulation, the impact of the signal-to-noise ratio and fluctuation of the coupling efficiency on null error has been obtained.

Strain measurement using frequency modulation fiber optic interferometer

The method for measuring the strain of an object using an optical fiber and a frequency modulation(FM) coupled cavity semiconductor laser is proposed.This method uses the coherent FM heterodyne principle of the Michelson interferometer and can avoid the π/2 nonreciprocal phase bias and phase shifting problem existing in general fiber optic interferential sensors, the maximum detection range is limited by the coherent length of the semiconductor laser and its relative factor.

基于双端Mach-Zehnder的电缆舞动监测系统设计

针对传统电缆舞动检测器在面对电磁干扰和持续供电时灵敏度低、信噪比差、安装复杂和需额外供电等问题,提出一种新型双端Mach-Zehnder(M-Z)电缆扰动监测系统.该系统采用双端光纤M-Z光路结构,可实现长距离、大尺度、多维度的在线监测和结构安全预警,从而实时定位舞动位置.该系统的检波器力学单元采用硅胶弹性体和黄铜质量块推挽式结构,经ANSYS软件进行参数化建模和有限元分析后,得出其固有频率为106.77 Hz,与实验所测数据的相对误差仅为1.65%.实验结果表明,该检测器在0~140 Hz内的相对灵敏度为41.25~66.78 dB (rad/Pa),对舞动信号具有较高灵敏度的检测能力.

Measurement of refrative index based on fiber Mach-Zehnder interference

In order to detect the refractive index of liquid with high precision,based on modular interference,Mach-Zehnder optical fiber refractive rate sensor was studied.Sensor structure is composed of ordinary single-mode fiber and multimode fiber,according to the singlemode multimode singlemode sequence to fuse together,and the fused optical fiber is used to process the taper.As a result,the diameter of the sensing head is about 10μm.Experimental results show that,as liquid refractive index increases range from 1.33 to 1.35,the loss peak of the transmission spectrum will shift to long wave direction.

MZI/FPI Fiber Optic Dual-parameter Sensor Based on a Double Cone and Air Cavity Structure(Invited)

This paper proposes a Mach Zehnder/Fabry Perot Interferometer(MZI/FPI)fiber sensor based on Single-mode Fiber(SMF)and Hollow-core Fiber(HCF),which has high sensitivity to temperature and lateral loads.The proposed device consists of two single-mode fiber cones formed by manually controlling the fusion splicer and an air cavity formed by fusing a section of hollow-core fiber.The structure of the sensor is a double cone cascaded air cavity.At the beginning of the design,we compared the basic transmission spectra of single cone structure and double cone structure experimentally,and therefore chose to use double cone structure and air cavity cascade.Light undergoes its first reflection at the first interface between the single-mode fiber and the air cavity structure,and its second reflection at the second interface between the air cavity structure and the single-mode fiber.The two reflected light waves produced by the two reflections form FP interference,which can be used to measure lateral loads.The transmitted light is excited through the first cone,and a portion of the core mode light is excited to the cladding,while another portion of the core mode light continues to propagate in the core.The light couples at the second cone,and the cladding mode light couples back into the core,forming MZ interference with the core mode light,which can be used to measure temperature.The use of hollow-core fiber to form an air cavity has little effect on transmitted light,while avoiding the problem of crosstalk in dual parameter measurements.By designing temperature and lateral load experiments,this article verifies the sensitivity characteristics of this sensor to temperature and lateral loads.A significant redshift phenomenon was observed in the temperature experiment.A significant redshift phenomenon also occurred in the lateral load experiment.Through wavelength demodulation,the experimental results show that the wavelength sensitivity of the sensor to temperature is 56.29 pm/℃in the range of 30℃to 80℃.The wavelength sensitivity of the sensor to lateral loads is 1.123 nm/N in the range of 0~5 N.In addition,we have prepared multiple sets of fiber optic sensors with this structure and conducted repeated experiments to verify that the sensing performance of this structure of fiber optic sensors for temperature and lateral load is relatively stable.Also,the different waist diameters of cones will have a certain impact on the transmission spectrum of MZ,while the length of the air cavity will also have a certain impact on the reflection spectrum of FP.This article lists some fiber optic sensors for dual parameter measurement of temperature and lateral load.Compared with the listed sensors,the fiber optic sensor proposed in this article has better sensitivity to temperature and lateral load.And the fiber optic sensor proposed in this article has a simple manufacturing process,low production cost,and good performance,which has certain prospects in scientific research and industrial production.

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.

Application of Wavelet Transform in Dual-differential Optical Fiber F-P Interferometric Micro-displacement Measurement System

Based on dual-differential comparing principle, an experimental system of optical fiber F-P interferometric micro-displacement measurement is introduced. It is capable of achieving the absolute displacement measurement, and wavelet transforms is adopted as theory fundament to extract the optical F-P interferometric characteristic signal and remove the noise, so its resolution can reach 0. 01 μm in the dynamic range of 0～ 1 mm.

全光纤Mach-Zehnder干涉仪及其在光纤自发布里渊散射测量中的应用

从理论上分析了全光纤 Mach- Zehnder干涉仪的分光原理 ,并将所研制的全光纤单通Mach- Zehnder干涉仪和双通 Mach- Zehnder干涉仪应用于自发布里渊散射光谱的测量 。

一个新型的基于全光纤Mach-Zehnder干涉仪BOTDR系统

报道了新型的分布式传感测量布里渊光时域反射 (BOTDR)系统 布里渊散射频移和强度均依赖于温度和应变 ,因此 ,BOTDR利用光纤中的自发布里渊散射作为测量信号可以实现分布式温度和应变测量 在BOTDR中 ,光源采用窄谱半导体激光器 ,并由声光调制器调制成脉冲光 ,经掺铒光纤放大器放大后 ,注入测试光纤以产生自发布里渊散射 利用双通Mach Zehnder干涉仪分离光纤背向散射中的自发布里渊散射与瑞利散射信号 ,实现了自发布里渊散射的直接检测 实验结果表明基于全光纤Mach

非平衡光纤Mach-Zehnder干涉仪偏振衰落及相位噪声分析

研究了非平衡光纤Mach Zehnder干涉仪因两束干涉光偏振态变化引起的偏振衰落和相位噪声问题。运用波导耦合理论和光纤偏振光传输理论,通过详细的推导,得到非平衡光纤Mach Zehnder干涉仪输出光强、可见度以及相位噪声的表达式,分析了干涉仪可见度、相位噪声与干涉仪输入光偏振态之间的关系,提出抑制偏振衰落和相移噪声的方法。

纤芯失配的光纤Mach-Zehnder折射率传感器

基于Mach-Zehnder干涉仪原理,利用光纤错位熔接技术设计并制作了一种单模光纤-多模光纤-单模光纤-错位熔接点-单模光纤结构的液体折射率传感器.传感器中的多模光纤和错位连接部分充当光耦合器;多模光纤在后面的单模光纤的纤芯和包层中激发出纤芯模和包层模,不同的模式有不同的模式折射率,经中间单模光纤传输到错位熔接点处时,不同模式光之间将产生光程差,经错位熔接点耦合成为导出光纤的纤芯模从而产生干涉.对该传感器输出的干涉光谱中干涉谷功率随外界溶液折射率变化的规律进行了理论分析和实验研究.结果表明：溶液折射率变化为1.358 9～1.392 2时,干涉谱中1 530 nm附近的干涉谷光功率与溶液折射率呈单调递增关系,可用于折射率的测量;折射率变化为1.372 0～1.392 2时,传感器响应曲线具有很好的线性度,线性拟合系数为0.998,对应的灵敏度为252.06 dB/RIU.该传感器制作简单、结构紧凑、成本低、灵敏度高,可用于生物医学领域液体折射率的实时测量.

双Mach-Zehnder光纤干涉传感系统中的偏振衰落控制

针对偏振衰落现象导致信号关联的二义性使分布式双Mach-Zehnder光纤干涉传感系统难以实现高精度定位的问题,提出了一种控制偏振衰落的方法来保持系统检测信号的稳定性。利用系统的偏振模型分析了偏振衰落的来源,指出传感光纤偏振特性的不一致使系统检测信号对输入偏振态敏感是造成信号相关性恶化的根本原因,据此提出控制输入偏振态、搜索偏振态工作点的抗偏振衰落思想。在此基础上通过分析输入偏振态的两个参量对信号相关系数的作用进一步明确了偏振控制对算法的要求,并利用模拟退火算法进行了验证。现场实验表明,该算法可快速搜索偏振态工作点,持续稳定系统检测信号的相关性;结果证实了提出的偏振衰落控制方法可行且有效。

基于3×3耦合器的非平衡光纤Mach-Zehnder干涉仪传输特性研究

研究了一般条件下基于3×3耦合器的非平衡光纤Mach-Zehnder干涉仪的传输特性。运用波导耦合理论和光纤偏振光传输理论,通过推导,得到干涉仪输出光强、可见度以及相位噪声的表达式,分析了干涉仪三路输出光强之间的相互关系,以及可见度、相位噪声与干涉仪输入光偏振态之间的关系。

埋入光纤Mach-Zehnder干涉仪检测复合材料梁的分层

将光纤Mach-Zehnder干涉仪的传感臂埋入到复合材料梁的中性层来检测梁的分层。不论梁是连续支撑还是简单支撑,均取得了很好的实验结果。通过用榔头连续下压梁,由光纤干涉仪可以得到一条输出曲线,从这条曲线就可以准确判断梁内部是否存在分层,以及分层的位置。

克服光纤Mach-Zehnder干涉仪信号衰落的新方法及分析

为了克服光纤Mach Zehnder干涉仪易受环境因素影响而引起偏置相位漂移从而导致输出信号衰落 (波动 )的问题 ,提出一种新的简单方法 ,即 :将干涉仪输出信号分为直流和交流两个分量 ,通过直流分量的大小来计算交流信号的补偿因子 ,以达到克服交流信号衰落、稳定检测传感信号的目的 在小信号测量情况下 ,该方法在很大范围内能有效抑制随机温度涨落等因素引起的信号衰落的问题