Hybrid Wavelength-Time-Domain Interrogation System for Multiplexed Fiber Bragg Sensors Using a Strain-Tuned Erbium-Doped Fiber Laser

A system for the interrogation of fiber Bragg grating (FBG) sensors using a strain-tuned EDF laser with linear cavity is described. An optical switch is spliced to one end of the laser cavity and connects one of two high-strength draw-tower fiber Bragg gratings (DTGs). The gratings are simultaneously tuned by a stretching device and act as the end reflector of the laser cavity. By applying a ramp signal to the actuator synchronized to the optical switch, the laser signal sweeps over two different wavelength intervals, depending on the connected DTG. This approach represents a hybrid wavelength-time-domain interrogation for multiplexed sensors and doubles the number of sensors that may be addressed when compared with single DTG scanning. In addition, the use of the DTG allows a fivefold increase in the strain tuned wavelength interval over standard fiber Bragg gratings. An example application is demonstrated where temperature inside an electrical motor is measured during operation.     

Nonlinearity Compensation of the Fiber Bragg Grating Interrogation System Based on an Arrayed Waveguide Grating

In this paper, we report on nonlinearity compensation for a solid-state fiber bragg grating (FBG) sensor interrogation system based on an arrayed waveguide grating (AWG) device. A lookup table with calibration data is used to improve system linearity. A reduction in the absolute value of the measurement error from 120 mustrain or 15degC to 4.8 mustrain or 0.6degC, respectively, is experimentally demonstrated.     

基于FPGA的FBG光纤光栅解调系统

研究并实现了一种基于FPGA(现场可编程门阵列)的FBG(光纤布拉格光栅)光纤光栅传感系统,运用FPGA以及上位机软件完成了G11620-512DA InGaAs(铟砷化镓)线阵探测器驱动、探测器数据采集转化、高斯拟合处理、数据网口传输,实现了FBG光纤光栅解调.实验结果表明,该系统在FPGA的控制下能够正常工作,其输出数据符合FBG反射光谱理论分析.     

Fiber Bragg Grating Sensor System With Two-Level Ring Architecture

This investigation proposes a fiber Bragg grating (FBG) sensor system with a two-level ring architecture. The survivability and capacity of a FBG for a multipoint sensor system are enhanced by adding remote nodes and optical switches in the two-level ring architecture. Additionally, to enhance the signal-to-noise ratio (SNR) of the sensor system, a fiber ring laser approach is utilized to construct the proposed two-level ring architecture. The fiber ring laser adopted herein yields the high SNR of the sensor system. The proposed system can increase the reliability of FBG sensor systems for multipoint smart structures.      

Fabry–Perot Microcavity Modes in Single GaP/GaNP Core/Shell Nanowires

Semiconductor nanowires (NWs) are attracting increasing interest as nanobuilding blocks for optoelectronics and photonics. A novel material system that is highly suitable for these applications are GaNP NWs. In this article, we show that individual GaP/GaNP core/shell nanowires (NWs) grown by molecular beam epitaxy on Si substrates can act as Fabry‐Perot (FP) microcavities. This conclusion is based on results of microphotoluminescence (μ‐PL) measurements performed on individual NWs, which reveal periodic undulations of the PL intensity that follow an expected pattern of FP cavity modes. The cavity is concluded to be formed along the NW axis with the end facets acting as reflecting mirrors. The formation of the FP modes is shown to be facilitated by an increasing index contrast with the surrounding media. Spectral dependence of the group refractive index is also determined for the studied NWs. The observation of the FP microcavity modes in the GaP/GaNP core/shell NWs can be considered as a first step toward achieving lasing in this quasidirect bandgap semiconductor in the NW geometry.     

High Sensitivity Fiber Bragg Grating Pressure Sensor Using Thin Metal Diaphragm

A high sensitivity pressure sensor design without a polymer transducer is demonstrated in this paper. The sensor uses a thin metal diaphragm as a pressure transducer instead of a polymer. The sensor is tested to a maximum pressure of 100 psi and has a sensitivity of 0.0115 nm/psi, which matches the calculated sensitivity of 0.0127 nm/psi. The sensor is provides accurate measurement of the pressure and shows good repeatability in its readings. The sensor is also tested at the flow loop of the University of Tulsa, and shows a good match with the pressure readings of the flow loop.     

内埋光纤光栅的复合材料层压板拉伸应变研究

利用内埋在复合材料层间的光纤光栅(Fiber Bragg Grating,FBG)传感器监测复合材料层压板在拉伸过程中的应变变化,并与复合材料层压板试样表面粘贴的应变片测得数据进行对比,同时研究了光纤光栅的埋植位置对复合材料力学性能的影响.探索了FBG传感器在复合材料应变监测中的有效性和可靠性.结果表明:内埋于复合材料层间的FBG传感器可以有效反映复合材料层压板在受到拉伸载荷过程中的应变变化,对比FBG传感器与应变片测得的实验结果,二者所测得的应变变化趋势吻合良好,而且埋植光纤光栅对复合材料层压板的拉伸强度影响较小.     

光纤光栅振动传感系统仿真研究与分析

由于光纤光栅传感器具有灵敏度高、动态范围宽、不受电磁干扰、成本低、体积小等优点,使其在传感领域具有很好的应用前景.光纤光栅传感技术已成为现代传感领域的一个重要研究方向,其在振动传感领域的应用也取得了一定的成就.本文针对悬臂梁式光纤光栅振动传感,将光纤光栅振动传感元件近似为惯性式振动系统,以其数学模型为基础,利用Matl...     

新型分布式布喇格光纤光栅传感系统的研究

提出了一种新型分布式布喇格光纤光栅(FBG)传感系统.为了满足一个大型工程同时监测上百个不同位置的要求,将这一百个点分成若干组,每组构成一个小区域,每个小区域由四个波长相同的光栅组成,这样就满足了在一条光纤上刻一百个光栅的要求.当某点温度发生变化时,该区域的最高温度可测得;若此最高温度超过警戒温度,则系统发出报警信号,进而对这个小区域进行整体降温处理.在理论分析的基础上,对多组不同波长的光纤光栅进行了温控对比实验,在10～110℃的温度范围内,FBG的中心波长随温度变化呈良好的线性,线性度达到99.6%以上.实验表明该系统具有精度高、适用于分布式多点测量的特点.     

A Parallel Multiplexed Temperature Sensor System Using Bragg-Grating-Based Fiber Lasers

A parallel multiplexed temperature sensor scheme using a Bragg grating-based fiber laser approach has been developed and evaluated. Multiple laser cavities were formed as the active gain media of the system using a common broadband chirped fiber Bragg grating (CFBG) and several normal FBGs, which were used as optical feedback elements, in conjunction with different lengths of erbium-doped fibers (EDFs). These gain media were externally pumped by light from a 1480-nm laser diode (LD) through a 1480-nm 1$times$4 splitter. Normal FBGs were used as the wavelength-selective and sensing elements of the laser system. Simultaneous laser action at three different wavelengths corresponding to channels 1, 3, and 4, respectively, was obtained using this scheme. The temperature was measured over the range from room temperature (27$^circhboxC$) to a maximum of 540$^circhboxC$, which shows the potential of the scheme for quasi-distributed sensor applications.     

光纤Bragg光栅用于三维编织复合材料结构的内应变测量

本文对应用光纤Bragg光栅传感器编入三维编织复合材料结构内部的测量进行了研究.首先简要介绍了光纤光栅的编入方法和传感原理.随后进行的实验结果显示由应变计及光纤光栅所得到的载荷-应变曲线都具有良好的线性关系,实验之间的结果符合得很好,表明光纤Bragg光栅传感器可以用来精确检测编织试件复杂载荷状态下的内应变.从而将会促进光纤光栅在3-D编织复合材料结构的内部结构检测和强度失效分析中的更广泛应用.     

分布式光纤光栅应变和温度同时测量系统

设计了分布式光纤光栅应变和温度同时测量系统,光源为时钟脉冲宽带光源,结合时分和波分复用技术解决光纤光栅传感网络的复用寻址问题,选用不同包层直径光纤相熔接的应变补偿法传感头设计方案,实现了温度和应变的同时测量.采用阵列波导光栅技术对传感信号进行解调,通过理论分析证实了系统方案的可行性.系统对应变和温度的测量范围为0～2500 με和25～120℃,误差分别为±17 με和±1℃.     

Interrogation of a Long Period Grating Fiber Sensor With an Arrayed-Waveguide-Grating-Based Demultiplexer Through Curve Fitting

Interrogation of a long period grating (LPG) fiber sensor with an arrayed-waveguide-grating (AWG)-based demultiplexer through curve fitting is investigated and experimentally demonstrated. In the interrogation system, the measured light intensities from the output of the AWG are used to reconstruct the selected resonant dip of the LPG sensor through curve fitting in the form of a linear combination of Gaussian functions. By monitoring the changes of the reconstructed LPG spectrum, including the center wavelength shift and the minimum attenuation variation, the sensor signals can be interrogated with good accuracy in real time. The center wavelength is obtained by calculating the first-order derivative of the fitting function. The minimum attenuation is obtained directly from the reconstructed spectrum. Since the interrogation system demonstrated is based on an all-solid-state optical device, it offers the advantages of compact size and high-speed interrogation with high potential for integration.      

Structural Health Monitoring of Cracked Aircraft Panels Repaired with Bonded Patches Using Fiber Bragg Grating Sensors

Structural health monitoring of cracked aircraft panels repaired with bonded patches for extending the service life of aging aircraft has received wide attention. In this paper, the identification of the locations and shapes of fatigue crack and disbond fronts in aircraft panels repaired with double-sided bonded patches using fiber Bragg grating (FBG) sensors is studied. The identification is performed by minimizing the difference between the detected and calculated reflection spectra of FBG sensors at multiple positions on the free surface of patches. The validity and effectiveness of the identification in practical use is verified by comparing the identification results with the exact ones.     

Strain Measurement Using Embedded Fiber Bragg Grating Sensors Inside an Anchored Carbon Fiber Polymer Reinforcement Prestressing Rod for Structural Monitoring

Results are reported from a study carried out using a series of Bragg grating-based optical fiber sensors written into a very short length (60 mm) optical fiber network and integrated into carbon fiber polymer reinforcement (CFPR) rod. Such rods are used as reinforcements in concrete structures and in tests were subjected to strain through a series of cycles of pulling tests, with applied forces of up to 30 kN. The results show that effective strain measurements can be obtained from the different sensors mounted along the rod. Additionally, the tests show that close agreement with the results obtained from the calibrated force applied by the pulling machine and from a conventional resistive strain gauge mounted on the rod itself is obtained. Calculations from strain to shear stress show a relatively uniform stress distribution along the bar anchor used. The results give confidence to results from various methods of in situ monitoring of strains on such CFRP rods when used in different engineering structures.     

Strain Measurement on a Rail Bridge Loaded to Failure Using a Fiber Bragg Grating-Based Distributed Sensor System

The paper reports results obtained from an unusual situation in structural monitoring—a “test-to-destruction,” measuring strain using a series of fiber Bragg gratings (FBGs) sensors on a decommissioned concrete Railway Bridge in ÖrnskÖldsvik, Sweden. The study formed part of the EU “Sustainable Bridges” Project. To undertake the study, FBG-based sensors were chosen and embedded in carbon fiber reinforced polymers (CFRPs) composite rods incorporated into grooves specially created in the concrete structure and interrogated using a compact system based on wavelength-division multiplexing (WDM). Throughout the study, the FBG sensors were continuously monitored, allowing the incremental increases in the strain to be seen and through the yield point of the carbon composite reinforcement. The sensors were able to follow the resulting induced changes in strain of over a range in excess of 4000 $mu varepsilon$ just prior to failure of the bridge and representing extreme levels of strain for such a mechanical structure. The measurements made with the FBG-based system were found to be in agreement with the changes expected in the structure (together with the embedded reinforcement), produced by the loading applied. The study has demonstrated the successful use of FBG-based technology premounted in “smart” carbon fiber composite reinforcements used in a test of this type on a typical bridge structure of a type found widely across the world.      

用相位模板法制备紫外光写入光纤布拉格光栅的研究

利用相位模板，在２４８ｎｍ ＫｒＦ准分子激光器光束的照射下，在国产高掺锗单模光纤中制作出了中波长为１５４７ｎｍ，峰值反射率约为１０％，带宽为０．６４ｎｍ的调制光纤由拉格光栅。