基于超长周期光纤光栅的高灵敏度扭曲传感器

利用高频CO₂激光脉冲写入的周期达数毫米的超长周期光纤光栅(ULPFG)，实验研究了这种新型ULPFG的扭曲特性，发现它的某些高阶谐振波长漂移与扭曲率之间具有良好的线性关系和方向相关性，其灵敏度可达0.2244nm/(rad/m)，是高频CO₂激光脉冲写入法写入的普通LPFG扭曲灵敏度的4倍.初步的理论分析表明，新型ULPFG横截面折变的非对称性以及导模与高阶包层模之间发生的耦合使得扭曲具有方向相关性和很高的灵敏度.基于这种ULPFG独特的扭曲特性，设计了一种可 关键词： 光纤传感 光纤光栅 2激光')" href="#">CO₂激光 扭曲测量 双折射     

一种基于新型长周期光纤光栅的动态增益均衡器

报道了一种用高频CO²激光脉冲写出的长周期光纤光栅的温度特性和弯曲特性.实验表明,这种长周期光纤光栅的波长漂移随温度的变化呈线性关系,它的透射峰幅值变化随弯曲量的变化也呈线性关系.基于这两种线性关系,通过控制新型长周期光纤光栅的谐振峰位置和幅度,动态平坦了一组掺铒光纤放大器增益谱线.实验结果表明在C波段32nm范围内掺铒光纤放大器增益谱线平坦度可动态调整为±0.7dB.     

Fiber grating sensors for high-temperature measurement

Two fiber grating sensors for high-temperature measurements are proposed and experimentally demonstrated. The interrogation technologies of the sensor systems are all simple, low cost but effective. In the first sensor system, the sensor head is comprised of one fiber Bragg grating (FBG) and two metal rods. The lengths of the rods are different from each other. The coefficients of thermal expansion of the rods are also different from each other. The FBG will be strained by the sensor head when the temperature to be measured changes. The temperature is measured based on the wavelength-shifts of the FBG induced by the strain. In the second sensor system, a long-period fiber grating (LPG) is used as the high-temperature sensor head. The LPG is very-high-temperature stable CO₂-laser-induced grating and has a linear function of wavelength–temperature in the range of 0–800 °C. A dynamic range of 0–800 °C and a resolution of 1 °C have been obtained by either the first or the second sensor system. The experimental results agree with theoretical analyses.     

Simultaneous measurement of temperature and strain using a long-period fiber grating with a micro-taper

An all-fiber Mach–Zehnder interferometer (MZI) consisting of a long-period fiber grating with a micro-taper is proposed for simultaneous measurement of temperature and strain. The experimental results demonstrate that the temperature and strain sensitivities of the proposed MZI are 83 pm/°C and ?2.6 pm/με, respectively. The strain sensitivity is 20 times as high as that of a long-period fiber written by CO₂ laser pulses combined with a fiber bitaper. In addition, the interferometer requires only a common single-mode fiber, and it is easy to fabricate and is inexpensive for temperature and strain sensing applications.     

基于新型长周期光纤光栅的低成本应变传感系统

首次利用高频CO2激光脉冲写入的长周期光纤光栅的边缘滤波效应，实现了静态与动态应变的测量.使用单波长输入光，光信号经过长周期光纤光栅衰减后进入光电探测器，最终输出电压信号.当对光栅施加应变时，其中心波长将发生漂移，由于光栅阻带的边缘滤波效应，光电探测器接收的光强会随之变化，测量其输出的电信号，可以得出光栅发生的应变大小与频率.对于静态应变测量，可分辨的最小应变小于10 με，精度为±10 με;在动态实验中,发现光栅能够响应5 kHz以上的动态应变.这种传感系统结构简单，成本低,响应快.     

长周期光纤光栅气敏薄膜传感器结构优化

基于三包层长周期光纤光栅模型,研究了包层表面涂覆一层溶胶凝胶气敏薄膜的长周期光纤光栅化学传感器的灵敏度Sn与薄膜光学参量(折射率n3和厚度h3)和光纤光栅结构参量(光栅周期、折变量和光栅长度)之间的关系。采用最优化数值方法,找到了获得高灵敏度所需的最佳膜层光学参量和光栅结构参量。理论计算表明,该类型传感器对膜层折射率的测量分辨率高达10-8。实验上制作了对乙醇气体敏感的传感器,并证实了传感器结构优化的必要性。     

基于激光瞬态特性的气体浓度光纤传感器

报道了一种基于掺铒光纤激光器瞬态特性的新型气体浓度传感器.用光纤环全反镜和光纤Bragg光栅(FBG)构成F-P线形腔，通过调节光栅的反射波长，使激光激射波长落在C₂H₂的一个较强的吸收峰1531.56 nm.激光激射延迟时间与激光器谐振腔损耗密切相关，气体浓度的改变将引起谐振腔损耗的改变，通过测量激光激射延迟时间可以获得气体的浓度.该装置分辨率及灵敏度由抽运光脉冲的高功率电平和低功率电平决定，传感器的动态测量范围由抽运光高功率电平决定.当高功率和低功率电平分别为25 mW和5.9 mW时,该传感器的灵敏度和分辨率分别为100 ppm/μs和20 ppm.     

Bend-insensitive long-period fiber grating sensors

A novel bend-insensitive long-period fiber grating (LPFG) sensor written using focused CO₂ laser pulses is demonstrated, for the first time, to our knowledge. It is found that the central wavelength shift of such a LPFG is only −0.018 nm even for a curvature of 1.1 m⁻¹ at the most bend-insensitive position of the LPFG. Experimental results show that the bend sensitivity of the central wavelength of the LPFG has a periodic distribution along its circular directions. Such a bend-insensitive sensor could be used to solve the problem of cross-sensitivity between bend and other measurands, such as temperature, strain or refractive index, which is an unsolved problem for LPFG sensors in practice. In addition, the bend sensitivity of the LPFG can be adjusted by selecting its circular positions.     

基于PCF-LPG的差分算法实现对光纤传感器的噪音消除

为了有效消除光源抖动及系统不稳定因素给光纤传感器带来的噪音干扰,提高光纤传感器的准确度,本文提出了一种基于光子晶体光纤长周期光栅的差分算法.利用光子晶体光纤长周期光栅良好的温度稳定性及宽光谱滤波特性,同时监测位于光子晶体光纤长周期光栅透射谱正负斜率线性区域内的两个信号功率变化.这两个信号是经同一路径到监测设备的,包含光源抖动以及系统其它不稳定因素带来的噪音干扰,对这两个信号进行差分处理即可有效消除噪音干扰,并将其应用于光纤环镜温度传感器.结果表明:通过基于光子晶体光纤长周期光栅的差分处理,在光源功率变化±10%的情况下,差分值基本保持不变,由此获得的温度测量值与真实值相对误差分别为0.04和0.03|与未引入差分算法相比,传感器准确度从约76%提高到约97%.本文提出的基于光子晶体光纤长周期光栅的差分算法可以有效消除光纤传感器内功率抖动所带来的噪音干扰,大大提高系统的准确度.     

长周期光纤光栅耦合模理论分析

长周期光纤光栅作为透射型光无源器件,以其在通信和传感领域具有广阔应用前景而引起人们的关注。要得到满足性能要求的光纤光栅,对其透射谱的分析是基础。通过耦合模方程确定了基模和一阶各次包层模之间的耦合常数。在设定的光纤光栅参数条件下,通过Matlab进行模拟得到了最终需要的长周期光纤光栅透射谱,并由此得出：长周期光纤光栅谐振波长出现的位置主要由光栅的周期决定,损耗大小可以通过调节光栅长度和折射率来实现。     

Simultaneous Measurement of Refractive Index and Temperature Using a Hybrid Fiber Bragg Grating/Long-Period Fiber Grating Configuration

Abstract

A fiber optic sensing system for simultaneous measurement of refractive index and temperature, based on a hybrid fiber Bragg grating/long-period grating arrangement is described. The experimental results show that this setup has a good performance in terms of linearity and sensitivity, the ratiometric output changes 4%/0.001 RIU and 3.6%/°C, respectively. The sensor resolution for the refractive index is ≈2 × 10^?5 RIU. The simultaneous measurement of the refractive index and temperature was demonstrated. The sensing configuration has the ability to be read-out in reflection and works in the telecommunications window.     

Dynamic strain measurement using two wavelength-matched fiber Bragg grating sensors interrogated by a cascaded long-period fiber grating

In this work, we describe a fiber Bragg grating (FBG) sensing system using two wavelength-matched FBG sensors for static and dynamic strain measurement. A cascaded long-period fiber grating (CLPG)-based demodulation technique has been used to interrogate the two wavelength-matched FBG sensors. Experimental results of static strain measurement show that the proposed system has a strain resolution of 1 με. This system has also been used for dynamic strain measurement. An eddy current displacement meter-based system has been used as a comparison measurement. Experimental results of dynamic strain measurement have proved that the FBG sensing system has a good performance in the measurement of dynamic strain. The results of static and dynamic strain measurement indicate that the sensing system using two wavelength-matched FBG sensors is superior to the single FBG sensor system.     

Controlling of symmetric and asymmetric mode coupling in long-period fiber gratings singe-side induced by long-pulse CO2 laser

We report a simple fabricating approach to control the mode couplings in long-period fiber gratings (LPFGs) through side exposing fiber to long-pulse-10.6-μm laser from a cheap, internally modulated CO₂ tube. By tuning focused-spot size on fibers, not only circularly symmetric mode coupling but also asymmetric mode couplings can be effectively achieved. Simulation of mode profiles in grating cross-section with Finite Element Method (FEM), and LPFG-cladding etching experiment with hydrofluoric acid (HF), support our explanation that asymmetric mode coupling in LPFGs depends on local refractive-index (RI) change within an azimuthally thin cladding layer, resulted from large-spot method induced deep melt flow on fiber surface during CO₂ laser irradiation.     

基于长周期光纤光栅的可变体机翼翼表温度测试系统研究

为实现可变体机翼翼表温度的高精度的实时检测,设计了一种基于长周期光纤光栅(LPG)的温度测试系统.该系统采用长周期光纤光栅作为温度传感元件,高双折射光纤环镜作为边缘滤波器件.在边缘滤波理论研究的基础上,提出了一种降噪增敏的算法.实验中将LPG粘贴在可变体机翼翼表材料的表面,当外界温度发生变化时,LPG的谐振波长发生偏移...     

新型波长解调技术在干涉型光纤传感器输出解调中的应用

提出了一种改进型边缘滤波波长解调技术,解决干涉型或谐振型光纤传感器输出的干涉谱波长的快速解调问题。该波长解调技术基于啁啾光栅和长周期光栅的光谱特点,以啁啾光栅作为矩形滤波器,提取传感器输出干涉谱的一个干涉峰;以长周期作为边缘滤波器,将干涉峰的波长信息转化为光强信息进行检测。该波长解调技术波长解调范围为传感器输出干涉谱的一个自由光谱范围(FSR),解调速度快,克服了当前波长解调技术中存在的测量范围与测量速度难以同时提高的问题,同时还具有系统成本低 ,体积小,能够灵活多路扩展的特点。详细介绍了解调系统的工作原理以及系统结构,并将其实际应用于一种干涉型光纤电流传感器输出干涉谱的波长解调中。通过实验证明电流传感器工作在工频及脉冲电流(脉冲宽度25 μs)情况下,该解调系统对传感器输出干涉谱具有准确、快速的解调效果。该研究对推进干涉或谐振型光纤传感器的实际工程化水平的提高具有重要意义。     

Torsion sensing with a fiber ring laser incorporating a pair of rotary long-period fiber gratings

We experimentally demonstrate a fiber ring laser for high-resolution torsion measurement, where the laser cavity consists of a Mach-Zehnder interferometer formed with a pair of long-period fiber gratings written in a twisted single-mode fiber by a CO₂ laser. The emitting wavelength of the laser provides a measure of the rate of the torsion applied to the grating pair, while the direction of the wavelength shift indicates the sense of the applied torsion. The narrow linewidth and the large side-mode suppression ratio of the laser can provide a much more precise measurement of torsion, compared with passive fiber-optic torsion sensors. The torsion sensitivity achieved is 0.084 nm/(rad/m) in the torsion range ± 100 rad/m, which corresponds to a torsion resolution of 0.12 rad/m, assuming a wavelength resolution of 10 pm for a typical optical spectrum analyzer. The ultimate resolution of the sensor is limited by the linewidth of the laser and could be an order of magnitude higher.     

基于激光器激射特性的新型应变传感系统

报道了一种基于掺铒光纤激光器瞬态特性的新型应变传感系统.用光纤环反射镜和光纤Bragg光栅(FBG)构成Fabry-Perot线型腔.腔内插入一个长周期光纤光栅(LPG)，其透射谱的中心波长为1574.4nm.FBG的带宽为0.23nm，不受力时其反射波长为1557.98nm，位于LPG的透射谱左沿；当FBG受力时激射波长向长波方向移动，激光通过LPG时透射损耗增大，腔损耗的增加将使激光激射延迟时间增加.因此，应变的大小可以通过激光产生的延迟时间来测量.这种新型应变传感器的分辨率和灵敏度由抽运光脉冲的高、 关键词： 应变传感 光纤激光器 时域测量 光纤Bragg光栅     

CO2激光脉冲边缘写入的长周期光栅折射率特性研究

报道了一种用高频CO2激光脉冲在普通通信光纤包层边缘单侧写入的新型长周期光纤光栅。研究发现,这种长周期光纤光栅的折射率变化主要发生在光纤包层区域,而纤芯的折射率变化较小;同时该光栅的附加损耗低于0.5 dB。进一步折射率特性实验研究表明,由于其特殊的折变结构,这种光栅具有较高的外界环境灵敏度,当外界折射率在1.41~1.45范围内变化时,其谐振波长漂移量高达15.52 nm,比实验测得的用传统方法写入的长周期光纤光栅谐振波长漂移量高出近3倍,这种光栅结构在光纤传感中将具有重要的应用。     

Optical fiber long-period grating with solgel coating for gas sensor

The novel long-period fiber grating (LPFG) film sensor is composed of the long-period grating coated with solgel-derived sensitive films. The characteristics of the transmissivity of the LPFG film sensor are studied. By analyzing the relation among the sensitivity Sn, the thin film optical parameters, and the fiber grating parameters, the optimal design parameters of the LPFG film sensor are obtained. Data simulation shows that the resolution of the refractive index of this LPFG film sensor is predicted to be 10(-8). Experimentally, a LPFG film sensor for detection of C(2)H(5)OH was fabricated, and a preliminary gas-sensing test was performed.     

基于光纤布拉格光栅与长周期光栅并联的集成光学传感器

为了提高光纤传感器的性能和进一步缩小传感器的尺寸,通过实验制备出一种基于光纤布拉格光栅(FBG)与长周期光栅(LPG)并联的新型集成光学传感器。该传感器中的FBG和LPG是利用飞秒激光直写技术直接在普通单模光纤中刻写的。FBG和LPG是并联关系,因此很大程度地缩小了传感器的长度。外界的温度和折射率的变化会引起FBG和LPG的谐振峰波长位置发生变化,据此对该集成传感器进行温度和折射率测量。实验结果表明:FBG谐振峰对折射率和温度的灵敏度分别为0 nm/RIU和12.98 pm/℃,而LPG在1 555 nm附近谐振峰对折射率和温度的灵敏度为196.46 nm/RIU和10.93 pm/℃。因此,根据双参数传感矩阵,该传感器可以对温度和外界折射率进行同时传感。