Spectrally scanned,repetitively pulsed erbium-doped fiber laser for spectral and temporal multiplexing of fiber Bragg grating sensors

An erbium-doped fiber laser that emits a series of spectrally scanned pulses is used to monitor an array of fiber Bragg grating (FBG) sensors. The cavity for this Fabry-Perot laser is formed by two spectrally selective reflectors: a rotating mirror-grating combination for scanning the reflectance peak wavelength and a fiber Fabry-Perot interferometer (FFPI) with a periodic reflectance spectrum. During a scan of the rotating mirror, the laser produces a set of Q-switched pulses over the 1522-1568-nm spectral range at each of the FFPI reflectance peak wavelengths. This laser is used to simultaneously demonstrate wavelength-division multiplexing of FBGs with reflectance peaks in different spectral regimes and time-division multiplexing of FBGs with overlapping spectra. The spectral location of the FBG peaks was determined to an accuracy of 1.4 pm.     

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.     

岩层变形检测的光纤光栅多点传感理论与工程应用

为了监测松散地层沉降变形,提出了一种用于钻孔中植入式光纤Bragg光栅传感器(FBG)的结构和传感网络系统.基于室内实验结果,给出了用于岩层变形检测的传感光栅波长带宽为6 nm,分析了多点传感信号分辨因子,山光源带宽决定的测试系统最大实际复用能力为6个传感器.设计并实现了一个由18个光纤光栅组成的具有特色的光纤Bragg光栅波分复用/空分复用混合阵列.工程实践表明,光纤光栅传感系统采用双同路布置.可提高系统下放后光纤光栅传感器的成活率.     

可分离温度影响的FBG应变测量方法

光纤布拉格光栅在通信和传感领域具有广泛的应用。利用光纤布拉格光栅中心波长的偏移，可以测量温度和应变等多种物理量，但必须解决光栅对温度和应变的交叉敏感问题。该文简要分析了光纤光栅作为传感器的基本原理及其优点，设计了利用参考光栅法分离温度影响以及利用掺铒光纤的自发发射放大特性分离温度影响的2种应变测量方法。最后，介绍了一种利用倾斜光纤光栅的主模和边模对布拉格光栅中心波长的偏移进行解调的方法，该方法成功地分离了温度对应变测量的影响。     

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.     

基于信号自相关原理的光纤光栅数字解调方法

为满足工程测试领域对光纤光栅波长漂移高分辨探测技术的需要,提出一种基于信号自相关原理的新型光纤光栅数字解调技术.该技术在可调谐滤波法的基础上,通过对信号序列采用自相关分析以实现对波长漂移的测量以及对传感光栅反射谱形状的识别,能够有效克服噪音对信号的影响.仿真结果表明：光纤光栅自相关数字解调方法可以准确测量光纤光栅波长的漂移,适用于传感光栅具有相同波长的变化范围.     

A novel time-division multiplexing fiber Bragg grating sensor interrogator for structural health monitoring

A novel fiber Bragg grating (FBG) sensor system for measurement of strain and temperature is proposed in this paper. The proposed sensor technique is based on time-division multiplexing (TDM). A semiconductor optical amplifier (SOA), connected in a ring cavity, is used to serve as a gain medium and switch. The SOA is driven by a pulse generator, which operates the SOA at different periods of time to select reflected pulses from a particular sensor. The FBG sensors have identical center wavelengths and can be deployed along the same fiber. This technique relieves the spectral bandwidth issue and permits the interrogation of up to 100 FBGs along a fiber, if the reflectivity of the individual sensors is sufficiently low to avoid shadowing effects. This system is particularly suitable for the application in structural health monitoring (SHM) where large numbers of sensors are required in wide measurement ranges.     

Application of optical time-domain reflectometry for the interrogation of fiber Bragg sensors

A reflectometric approach is proposed for the polling and multiplexing of sensitive elements on fiber Bragg gratings (FBGs). The method is based on the power measurement of the radiation reflected by the FBG using a conventional fiber-optic time-domain reflectometer. The multiplexing of sensors is based on the time separation of signals. Requirements on the Bragg diffraction gratings that provide the linear dependence of the received signal on the FBG mechanical stress and temperature are determined. In the measurements of the FBG relative elongation and temperature, the threshold sensitivities are 0.8 × 10^?4 (80 μstrain) and 5°C, respectively. Due to its simplicity and efficiency, the reflectometric method of FBG polling and multiplexing can be used to solve various measurement problems, in particular, the safety monitoring of the stressed-strained elements in building structures.     

Partial scanning frequency division multiplexing for interrogation of low-reflective fiber Bragg grating-based sensor array

Interrogation using partial spectrum scanning for a low-reflective fiber Bragg grating (FBG)-based sensor array is proposed. The sensor head is a Fabry–Perot interferometer (FPI) consisting of low-reflective fiber Bragg gratings. An FPI consisting of low-reflective FBGs (FBG-FPI) has a spectrum with a sinusoidal structure with a period determined by the length of the FBG-FPI. Multiple point sensing is possible by installing multiple low-reflective FBG-FPIs on one fiber and analyzing the reflection spectrum of that fiber by the frequency division multiplexing method. A coherent wavelength-swept light source is necessary to acquire the reflection spectrum; however, but the sweep speed of a commercially available wavelength-swept light source that satisfies the condition is only approximately several tens of hertz. Therefore, we propose to conduct a wavelength sweep by injection current modulation of a laser diode. Wavelength sweeping with a modulated laser diode allows fast sweeping at 100 Hz or more, and the sweep range is as narrow as several hundred picometers. Reading only a part of the reflection spectrum of a low-reflective FBG-FPI sensor array using a modulated laser diode enables high-speed multipoint measurement through frequency analysis. Theoretical requirements for successful interrogation using the partial reflection spectrum are shown. A demonstration experiment to simultaneously measure strain applied to two low-reflective FBG-FPI sensors with a measurement time of 10 ms is reported.     

优化光纤光栅传感器匹配光栅解调方法的研究

利用悬臂梁调谐和两个并联二次反射匹配解调光栅的方法实现了光纤布喇格光栅(FBG)传感器的高精度大范围应变传感测量.通过并联方式,选择合适的匹配光栅波长,增大了可检测的应变范围,同时解决了双值问题.应变传感信号经两路解调光栅解调,并由数据采集卡采集后,由计算机进行两路并联信号的综合处理后获取更准确的结果,使得系统性能得到提升和优化.试验结果与理论分析一致.     

中心波长1080 nm的高功率光纤光栅研制与测试

介绍了基于紫外光侧写和相位掩模法制作双包层光纤光栅的工艺,制作了一对中心波长1080 nm的光纤光栅,测试光谱得到其反射谱带宽分别为2 nm和1 nm。采用自制的光纤光栅搭建了一个高功率光纤振荡器,得到最高502 W的激光输出,并测试了输出激光的光谱和光束质量。     

A linearity interrogation technique with enlarged dynamic range for fiber Bragg grating sensing

An exact linearity interrogation technique with enlarged dynamic range for fiber Bragg grating (FBG) sensor has been analyzed theoretically and demonstrated experimentally. The technique bases on two matched FBGs for receiving the reflected signal from the sensor FBG and two photodiodes (PDs) for collecting the reflected signal from the two receiver FBGs. The linear expression between the nature logarithm of the output ratio of the two PDs and Bragg wavelength of the sensor FBG is obtained on the condition that the bandwidths of the two receiver FBGs being equal to each other. The wavelength of the sensor FBG can be interrogated simply and accurately by the linearity technique according to the expression. In addition, a new tunable paralleled matched gratings interrogation scheme is proposed. The interrogation range can be enlarged and multiple FBG sensors can be interrogated simultaneously with the tunable interrogation scheme.     

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.     

基于三角波驱动法珀可调谐滤波器的光纤光栅解调偏差校正算法

为了校正解调系统在三角波上升行程和下降行程对光纤布拉格光栅(FBG)波长解调结果出现的偏差,提出一种采样点相对位置的校正算法。将三角波2个扫描行程的FBG波峰分别映射到相应的标准具原始数据中,再对2个映射波峰在标准具光谱中的相对位置偏差进行校正,达到减小解调偏差的目的。实验采用2支不同波长的FBG进行验证,结果显示,经过校正,FBG1将三角波上下扫描行程的解调偏差从12.053 pm减小到了0.476 pm,FBG2将该解调偏差从12.101 pm减小到了0.427 pm,2支传感器的解调偏差相比校正前分别减小了25.3倍和28.3倍。     

Fiber-fault monitoring technique for passive optical networks based on fiber Bragg gratings and semiconductor optical amplifier

A novel monitoring method for in-service fault indemnification in passive optical networks (PONs) is proposed and demonstrated experimentally. The proposed monitoring technique is based on fiber Bragg grating (FBG) sensors and fiber laser scheme, and a semiconductor optical amplifier (SOA) is used to serve as a gain medium. By detecting the number of the wavelength lasing, the fiber-fault can be monitored without affecting the in-service channels. Moreover, the strain behavior on the FBGs has also been discussed.     

Industrial and medical applications of fiber Bragg gratings(Invited Paper)

The uses of optical fibers are numerous, and over the past few decades, they have extended from optical fiber communications to a wide variety of sensing applications. In particular, fiber Bragg grating(FBG) sensors inscribed in single-mode optical fibers offer significant advantages over more conventional electrical sensors and have been successfully deployed in many different industries. In this Review, we review the applications of intrinsic FBG pressure and flow sensors in oil and gas and the deployment of FBG sensing networks in railways.The promising prospect of using polymer FBGs in wearable medical devices is also described.     

All-fiber actively Q-switched fiber laser tuned by a pair of temperature controlled fiber Bragg gratings

We report an all-fiber actively Q-switched erbium-doped fiber laser, where the linear laser cavity mirrors are composed of two fiber Bragg gratings (FBGs). The laser oscillation wavelength could be tuned by this pair of temperature controlled FBGs. The Q-switching is achieved by an all-fiber phase modulation device. Using this system, we could obtain stable Q-switched laser pulses output, which could be optimized by tuning the reflection wavelengths of the two FBGs to be adjacent to each other. Instead of being modulated by the FBG filter in high-speed oscillation, this fiber laser system is operating in the Q-switched regime using an all-fiber phase modulator, producing a more stable laser output spectrum.     

Experimental research on a novel fiber-optic cantilever-type inclinometer

Experimental setup for tilt measurement and a novel signal detection method for demodulation of fiber Bragg grating (FBG) wavelength shift are proposed. Being attached, respectively, on the upper and lower surface of only one single pendulum-type cantilever element, only a couple of matched FBGs are used for both tilt angle sensing and wavelength shift signal demodulating. So the received light power will change due to the split of the two reflected spectra of FBGs, which corresponds to the tilt angle. In addition, the cross-sensitivity effect of FBG-based sensors will be solved automatically due to a differential signal process method. Experimental results indicate the measurement accuracy is about ± 0.03°, and measurement resolution is estimated to be about 0.002°.     

Active temperature compensation design of sensor with fiber gratings

A technique for compensation of temperature effects in fiber grating sensors is reported. For strain sensors and other sensors related to strain such as electromagnetic sensors, a novel structure is designed, which uses two fiber Bragg gratings (FBGs) as strain differential sensor and has temperature effects cancelled. Using this technique, the stress sensitivity has been amplified and gets up to 0.226 nm/N, the total variation in wavelength difference within the range of 3-45 ℃ is 0.03 nm, 1/14 of the uncompensated FBG.The structure can be used in the temperature-insensitive static strain measurement and minor-vibration measurement.     

基于CDMA的布拉格光纤光栅传感系统的仿真分析

讨论了光纤光栅传感系统中常用的复用技术及其限制,阐述了利用CDMA技术实现光纤布拉格光栅阵列波长解调的复用方式,对系统的原理和性能进行了理论分析。在此基础上通过MATLAB做了基于CDMA的光纤光栅传感仿真分析,仿真结果表明该方法能区分反射波长重叠的光栅,从而提高FBG网络复用的频带利用率。