Combined time-wavelength interrogation of fiber-Bragg gratings based on an optical time-domain reflectometry

A reflectometric method for the combined time-wavelength multiplexing of the fiber-Bragg-grating (FBG) signals is proposed. The method is based on the spectral filtering of the probe pulses generated by a fiber-optic reflectometer using a bandpass filter consisting of a fiber circulator and FBG. The interrogated Bragg gratings are recorded on a fiber line in groups with identical resonance wavelengths inside groups and different wavelengths from different groups. The separation of the signals of FBGs that have different resonance wavelengths is due to the tuning of the filter passband, and the separation of the signals of FBGs with identical wavelengths involves the time separation of the responses of the Bragg gratings to the probe pulse. The threshold sensitivity of the method in the measurement of the relative elongation of FBG is 0.5 × 10^?4. The considerable practical prospects of the method are related to its simplicity, reliability, and the application of the conventional reflectometric equipment.     

Differential reflectometry of FBG sensors in the wide spectral range

The paper presents a reflectometric technique for interrogation of multiple fiber Bragg grating (FBG) sensors based on conventional optical time domain reflectometry (OTDR). The method proposed rests on the differential measurement of FBGs’ response to a short probing laser pulse. Implementation of differential measurement principle using several reference FBGs allowed us to eliminate the susceptibility of the system to intensity fluctuations as well as to increase the measurement range as compared to the previous developments. The experimental threshold sensitivity amounted to ∼50 microstrain with the measurement range being defined by the number of reference FBGs and limited only by optical fiber tensile strength. Due to its simplicity, efficiency and usage of conventional OTDR equipment the proposed FBG interrogation technique can find a wide range of applications dealing with strain and temperature measurements.     

A large capacity sensing network with identical weak fiber Bragg gratings multiplexing

A quasi-distributed optical fiber sensing network with large multiplexing capacity, which is based on identical weak fiber Bragg gratings, is proposed, theoretically analyzed and experimentally studied. The key technique is the demodulation technology named “Optical wavelength time-domain reflection (OWTDR),” which utilizes the optical power variation of reflected sensing signal in both time domain and wavelength domain. The influence of reflectivity of fiber grating, interval between adjacent gratings and transmission loss of delay fiber on the multiplexing capacity of sensing system are discussed. Analyzed results demonstrate that this sensing scheme can effectively increase the multiplexing capacity of sensing system up to 1000, implement multi-point synchronous measurement and reduce the cost of signal demodulation. 9 Identical weak fiber Bragg gratings with the same Bragg wavelength of 1536.651 nm, reflectivity of 6%, bandwidth of 0.07 nm are written in series to investigate the performance of the proposed scheme.     

光纤光栅多参数桥梁结构监测系统的研究

从土木工程应用的实际情况出发,利用光纤光栅传感器具有波长绝对编码和易于复用的特点,提出工程化同时测量温度、应变和压力的全光栅型低成本分布式传感方案。设计了基于连续波调频技术的光纤光栅多参量桥梁结构监测系统,将光频域反射复用与波分复用技术相结合,实现分布式光栅传感网络的寻址,提高了系统复用容量。实验表明：所设计的传感系统能够准确监测结构重要部位的内部应变及车流量等参数,为桥梁结构的静、动载测试提供了准确的数据,同时也为桥梁的工作状态评估和健康诊断提供了依据。     

A novel successive demultiplexing scheme based on optical-CDMA balanced demodulation for FBG sensor systems

In order to increase the multiplexing density of the fiber Bragg gratings （FBGs） for a low cost per-sensor, based on the analysis of the spectrum shadow distortion （SSD）, a novel successive demultiplexing scheme for FBG sensors has been developed. It is based on the optical cade division multiple access （CDMA） balanced demodulation. A high-density multiplexing-demultiplexing system for FBG sensors has been designed, and corresponding simulation carried out has demonstrated that the FBG sensors＇ reflective signals can still be obtained accurately and respectively, even if FBG sensors＇ operating bandwidths heavily overlap. The SSD has been greatly mitigated.     

调频连续波分布式光纤布拉格光栅复用系统

研究了利用调频连续波(FMCW)技术对分布式光纤布拉格光栅(FBG)复用系统进行寻址的基本原理;仿真分析了FBG传感器复用距离是系统最小分辨距离的整数倍或非整数倍时,对频谱信号的影响;搭建了基于FMCW的FBG复用系统实验平台,当传感距离1000m时,分别验证了不同扫描周期与复用系统差频信号的线性关系,及不同扫频范围与系统差频信号的线性关系。实验结果表明:FBG复用距离是系统最小分辨距离整数倍时,在测量距离1100 m范围内,系统测量最大误差为243 Hz,最大相对误差小于5%,可以实现FBG传感器的地址查询功能。     

Multiplexing fiber bragg grating sensors

Abstract

Bragg reflection gratings and out-coupling taps for sensors can be written holographically within the core of many commercial fibers available today. The gratings appear to be permanent and have been tested to temperatures in excess of 500°C. Quasi-distributed temperature, strain, pressure, chemical, and interferometric sensors can be made with the wavelength selective, reflection gratings, and taps. The fiber gratings, and the different types of sensors they can make, conveniently lend themselves to (wavelength-division multiplexing) WDM, (time-division multiplexing) TDM, and (frequency-division multiplexing) FDM types of multiplexing schemes. Instrumentation to detect the multiple sensors and measure their spectral shift for localized and quasi-distributed sensing is currently under development.     

Simultaneous measurement of the temperature and force using a steel cantilever soldered with a partially nickel coated in-fibre Bragg grating

A method for the simultaneous, independent measurement of temperature and force using a single in-fiber Bragg grating (FBG) sensors was proposed and demonstrated. The FBGs were partially metallized using a partial nickel coating method. A Bragg reflex peak was successfully divided into two reflex peaks during the partial nickel plating process. The metallized part of the FBG was soldered on a steel cantilever, and the non-metallized part hanged in air. Using a structure that is composed of the steel cantilever soldered with a dual-wavelength FBG, the temperature and pressure can be simultaneously measured and discriminated. The metallized part of the FBG is highly temperature-sensitive (about 26.1 pm/°C), and for the non-metallized part the original Bragg wavelength of the FBG remains unchanged. The force sensitivity of the metallized part which soldered on the cantilever remained at 82 pm/N from 30 to 90 °C.     

基于密集波分复用技术的Bragg光栅水听器

论述了用Bragg光栅制作水听器的原理和意义,利用光纤通信的密集波分技术,实现声压信号动态解调.采用压力增敏材料对Bragg光栅封装来增加其响应灵敏度,为避免温度变化引起光栅交叉敏感,在室温23±1℃条件下进行试验,给出实验结果.实验表明:基元水听器的频率响应平坦度好,信号输出稳定.同时采用密集波分技术动态解调声信号方案是可行的.     

基于啁啾光纤光栅的粮仓测温网络研究

为了解决传统光纤光栅测温系统中单根光纤上带光纤光栅探头数量少、回波光强弱以及复用能力差的问题,设计研究了基于啁啾光纤光栅的测温系统。通过啁啾调制技术提高了回波光的带宽,从而增强了信号的可处理性并大大提高了带探测点位的数量。推导了啁啾调制的光栅周期表达式,给出了调制方法及波长范围。实验采用LPT-102型宽带光源与F-P光纤解调仪等,调制带宽为1 535.0～1 555.0 nm,并结合WR-201型温度传感器作标定。对20～60 ℃范围内每1 ℃改变进行测试,实验结果显示,传统光纤光栅探头与啁啾光纤光栅探头的测试温度误差相近,都符合设计要求。相比而言,啁啾FBG的测试数据对应的波长偏移具有较为明显的单调线性的特征,即数据稳定性更高,同时,采用啁啾FBG的系统带光纤光栅探头数量明显优于传统光纤光栅测温系统。由此可知,本系统在不增加光纤个数及不降低温度测试精度的基础上,实现了大幅提高带探测点位数量的设计要求。     

光纤布拉格光栅法布里-珀罗腔纵模特性研究

分析了光纤布拉格光栅构成的法布里-珀罗（F-P）腔的透射谱特性，讨论了光栅带宽，反射系数相位因子以及腔长对F-P腔透射特性的影响，并对F-P腔随温度和应变的特性进行了分析，然后给出如何设计在光栅中心耦合波长处单模运转的法布里-珀罗腔.并提供了数值模拟结果和实验结果. 关键词： 光纤布拉格光栅 法布里-珀罗（F-P）腔 光纤激光器     

Multiple fiber Bragg grating interrogation based on a spectrum-limited Fourier domain mode-locking fiber laser

A novel fiber Bragg grating (FBG) sensing system based on a spectrum-limited Fourier domain mode-locking (SL-FDML) fiber laser is proposed. Multiple FBGs cascaded in a long fiber are utilized as both the sensors in the system and the wavelength-selected components in the SL-FDML fiber laser. Both wavelength-division multiplexing and spatial-division multiplexing techniques are demonstrated for interrogation of multiple FBGs by mapping the wavelength measurement to the time measurement and by adjusting the driving frequency of the SL-FDML fiber laser. The proposed FBG sensing system, employing techniques of the wavelength- and spatial-domain interrogation of multiple FBGs, can be used in remote and quasi-distributed multipoint sensing.     

基于光栅透射光斯托克斯参量的实时压力传感方法及性能优化

提出了基于光纤光栅透射光斯托克斯参量测量的新型实时压力传感方法。深入分析了透射光第一斯托克斯参量和压力所致线双折射之间的单调变化关系。分析表明,入射线偏振光入射角度以及相应测量波长点的选择对系统灵敏度、线性度及动态范围有重要影响。利用光纤光栅和高速在线检偏器搭建了实时压力测量系统,实验数据验证了压力和透射光第一斯托克斯参量之间的单调变化关系,证明了此方法的可行性。最后对实验误差和系统性能进行了分析并提出了改进方案。     

一种基于外差探测的光纤Bragg光栅温度传感器

提出了一种基于光纤Bragg光栅的温度传感器，阐述了光纤Bragg光栅的温度传感机理，用2个相同的光纤Bragg光栅构成折叠式Mach Zehnder(M Z)干涉仪，其中一个光栅作为参考臂，另一个作为传感臂：采用外差探测技术来测量外界的温度物理量。当温度发生变化，Bragg光栅的波长也随之改变。外差探测用来探测传感臂和参考臂由于温度变化引起的输出信号的频率差异。对其动态测量范围和灵敏度也进行了分析。     

光纤光栅振动传感匹配检测方法的研究

介绍了用匹配光纤布拉格光栅（FBG）对振动传感进行直接的光强调制，从而完成传感及解调过程的方法，首先从理论上推导了光纤光栅的反射，透射谱的表达式，对光纤光栅的传感机制给出了定性的解释，并建立了数学模型进行模拟，进而报道了利用匹配光纤光栅进行单点解调，将振动传感信号变为解调光栅的输出光强信号，从而进行检测的方法，实验结果与理论吻合得很好，证明该方法是可行的。     

新型光纤光栅水声传感器的研究

提出了一种新型的光纤布拉格光栅(FBG)水声传感探头结构以及光纤光栅传感信号的自解调方法。利用一对匹配光栅构成推挽结构,实现了传感-解调的合二为一,大大地减小了系统的复杂度;并通过筒状弹性体结构,解决了裸光纤光栅测量水声信号的灵敏度过小的问题,并具有温度补偿作用。仿真与初步实验结果表明,该水听器探头的测量动态范围超过100 dB,在100~200 dB re 1μPa的水声压范围内,测量灵敏度为0.36 nm/Mpa。     

应用平衡双光纤光栅动态解调技术测量应力的研究

报道了一种基于解调技术使用双光纤光栅测量张力的方法。在外界拉力下一个光纤布拉格光栅反射波长的漂移被转变成从另一个被压电陶瓷片调制的光栅反射的光脉冲间隔的变化。实验表明，当测量一个40N以内的力时，测量精度可达到2．5mN。     

光纤光栅传感器交叉敏感问题研究

交叉敏感问题是光纤光栅传感器在实际应用中需面对的一个关键问题。从光纤Bragg光栅的传感理论出发，分析了光纤光栅在同时测量应变和温度时引起交叉敏感的物理机理，建立了带有温度-应变交叉灵敏度系数的光纤Bragg光栅反射波长方程。利用双波长矩阵算法针对上述建立的光纤光栅方程进行了误差分析，获取了在交叉敏感情况下温度和应变的相对误差曲线图。结合相对误差表达式和曲线图分析讨论了交叉敏感对测量带来的影响。结果表明在温度和应力测量中随着测量温度或者应变变化量的增大，忽略交叉敏感项而带来的测量误差越来越明显。     

光纤布喇格光栅作为增益均衡器的掺铒光纤EDFA放大器

采用平均反转率模型分析了带光纤布喇格光栅的增益平坦掺铒光纤放大器,其输出增益可由一组耦合超越方程描述,而非耦合微分方程,同时讨论了用于增益平坦的布喇格光栅的最佳位置设计作为增益建模和最佳设计实例,对于输入功率0.5mW位于1545～1552nm的8个波长信道,得到的输出增益不平坦度小于0.05dB.最后还证实了布喇格光栅作为增益均衡器具有高输出功率和功率转换效率的优越性.     

Analysis of multimode BDK doped POF gratings for temperature sensing

We report a temperature sensor based on a Bragg grating written in a benzil dimethyl ketal (BDK) doped multimode (MM) polymer optical fiber (POF) for the first time to our knowledge. The thermal response was further analyzed in view of theory and experiment. In theory, with the order of the reflected mode increasing from 1st to 60th order, for MM silica fiber Bragg grating (FBG) the temperature sensitivity will increase linearly from 16.2 pm/°C to 17.5 pm/°C, while for MM polymer FBG the temperature sensitivity (absolute value) will increase linearly from ?79.5 pm/°C to ?104.4 pm/°C. In addition, temperature sensitivity of MM polymer FBG exhibits almost 1 order larger mode order dependence than that of MM silica FBG. In experiment, the Bragg wavelength shift will decline linearly as the temperature rises, contrary to that of MM silica FBG. The temperature sensitivity of MM polymer FBG is ranged from ?0.097 nm/°C to ?0.111 nm/°C, more than 8 times that of MM silica FBG, showing great potential used as a temperature sensor.