Experimental investigation of pre-irradiation effect on radiation sensitivity of temperature sensing fiber Bragg gratings

The effect of pre-irradiation on radiation sensitivity of fiber Bragg gratings(FBGs) is verified experimentally.FBGs are fabricated in photosensitive optical fibers and single mode fibers with Ge-concentration in a range from 3 mol% to 23.37 mol% in the core.In experiments,the FBGs are subjected to twice γ-radiation exposures to a Co60 source at a dose-rate of 0.1 Gy/s up to a total dose of 50 kGy.Pre-irradiation treatment can reduce the temperature sensitivity variation of FBGs by 18.12%-35.91%,as well as Bragg wavelength shift(BWS) by 8%-27.08 %.Our research demonstrates that pre-irradiation treatment is a feasible method to improve the radiation tolerance of FBGs.     

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。     

温度补偿的光纤光栅应力传感系统的研究

提出并实验了一种有温度补偿的用于测量应力的光纤光栅传感系统。该系统用一组光纤光栅作为温度传感元件 ,对另一组应力传感的光纤光栅作温度补偿 ,有效地消除了由于温度变化而带来的应力测量误差。用一个应变仪作为系统的读出设备 ,使系统的测量结果的线性拟合度达 0 999。     

Sensing properties of fiber Bragg gratings in small-core Ge-doped photonic crystal fibers

We report about fiber Bragg gratings (FBGs) inscribed in two different types of small-core Ge-doped photonic crystal fibers with a UV laser. Sensing properties of the FBGs were systematically investigated by means of demonstrating the responses of Bragg wavelengths to temperature, strain, bending, and transverse-loading. The Bragg wavelength of the FBGs shifts toward longer wavelengths with increasing temperature, tensile strain, and transverse-loading. Moreover, the bending and transverse-loading properties of the FBGs are sensitive to the fiber orientations. The reasonable analyses for these sensing properties also are presented.     

荧光光纤光栅传感特性的实验研究

在载氢掺铒光纤上写入Bragg光纤光栅,得到新型光子学器件-荧光光纤光栅.分别对其Bragg波长（λB）及荧光寿命（τ）的温度（T）及应变（ε）响应特性进行了实验研究,并且给出了λB和τ分别关于（T,ε）的拟合方程.实验结果表明：荧光光纤光栅的λB对T和ε的响应具备一般Bragg光纤光栅的优良特性,测得温度灵敏度为11.1pm /℃,应变灵敏度为1.19pm/με;而且τ对T和ε的响应也具有良好的线性关系,温度灵敏度为0.59 μs/℃,应变灵敏度为6.16 ns/με.实验结论为解决温度应力交叉敏感、实现温度应力的同时监测提供一条新颖的途径.     

Optic sensors of high refractive-index responsivity and low thermal cross sensitivity that use fiber Bragg gratings of >80 degrees tilted structures

For the first time to the authors' knowledge, fiber Bragg gratings (FBGs) with >80 degrees tilted structures have been fabricated and characterized. Their performance in sensing temperature, strain, and the surrounding medium's refractive index was investigated. In comparison with normal FBGs and long-period gratings (LPGs), >80 degrees tilted FBGs exhibit significantly higher refractive-index responsivity and lower thermal cross sensitivity. When the grating sensor was used to detect changes in refractive index, a responsivity as high as 340 nm/refractive-index unit near an index of 1.33 was demonstrated, which is three times higher than that of conventional LPGs.     

Multiwavelength Raman-fiber-laser-based long-distance remote sensor for simultaneous measurement of strain and temperature

We propose a simple and flexible multiwavelength Raman-fiber-laser-based long-distance remote-sensing scheme for simultaneous measurement of strain and temperature by use of fiber Bragg gratings. By combining two uniform fiber Bragg gratings with a tunable chirped fiber grating, we readily achieve simultaneous two-channel sensing probes with a high extinction ratio of more than approximately 50 dB over a 50-km distance. When strain and temperature are applied, lasing wavelength separation and shift occur, respectively, since the two uniform fiber Bragg gratings have identical material composition and different cladding diameters. This allows simultaneous measurement of strain and temperature for long-distance sensing applications of more than 50 km.     

Multiplexed reflective-matched optical fiber grating interrogation technique

The multiplexed-reflective matched fiber grating interrogation technique was presented in this paper.The interrogation technique was based on the use of two (or more) wavelength-matched fiber Bragg gratings (FBGs) to receive the reflected signal from the sensing FBG. The two (or more) matched gratings were arranged parallelly and used as filters to convert wavelength into intensity encoded information for interrogation. Theoretical and experimental results demonstrated that the interrogation system is immune to the source fluctuation and cross-sensitivity effect between temperature and strain, and also can enlarge the dynamic range.     

Gamma induced changes in Makrofol/CdSe nanocomposite films

We applied an ex-situ casting procedure to prepare a nanocomposite (NCP) from Makrofol polycarbonate (PC) and CdSe nanoparticles. The CdSe nanoparticles were prepared by a thermolysis procedure in the presence of N₂ gas flow. Rietveld refinement of x-ray data illustrated that the CdSe adopts a cubic zinc blend structure of 6.057 Å lattice parameter and 2 nm typical grain size. Samples from the prepared NCP were exposed to γ dosages (20 kGy-250 kGy). The modifications induced in the NCP films owing to γ dosages have been studied. The γ irradiation (50 kGy-250 kGy) causes crosslinks that reduce the optical bandgap from 4.15 eV to 3.81 eV, associated with an increase in dielectric parameters and refractive index. This is attributed to an increase in the mass fraction of the disordered regions as specified by x-ray diffraction. The PC-CdSe NCP was found to have a reaction to color modification which makes it suitable for saleable reproduction on a printing press.     

用超磁致伸缩调谐光纤光栅的光分/插复用器

提出并研究了一种新型多信道切换的全光分/插复用器,它主要由光纤Bragg光栅(FBG)和一对光环行器组成.采用了一种高效的超磁致伸缩材料(GMM)使FBG产生有效的Bragg波长偏移.用控制电流来调控FBG的应变和Bragg波长偏移.用4只相同的FBG与波长叠加技术相结合,可建立能提供15种不同下路信道方式的OADM.     

Dynamic strain monitoring by wavelength locking between two fiber Bragg gratings fiber sensing system

We demonstrated a fiber sensing system using the method of wavelength locking of two identical fibers Bragg gratings (FBG) to interrogate the wavelength shift by directly measuring the intensity of the reflection from the sensing Bragg grating. The light source of the fiber sensing system is an EDFA fiber ring laser pumped by a 980 nm laser diode and a narrow bandwidth fiber Bragg grating for the filter of the ring laser resonator. The wavelength shift is converted to the intensity deviation of the reflection from the sensing FBG under strain variation, and is able to achieve real-time sensing of the dynamic strain sensing in civil engineering. The characteristics and key factors to maintain stability of the dynamic strain sensing system are discussed.     

基于长周期光纤光栅的FBG解调方法北大核心CSCD

研究了基于长周期光纤光栅(long-period fiber gratings,LPFG)的光纤布拉格光栅(fiber Bragg gratings,FBG)解调方法,该方法利用LPFG的透射谱作为边沿滤波器解调FBG,其解调性能主要取决于LPFG的透射光谱深度。详细分析了CO_(2)激光写制法对透射光谱的影响,制作了透射光谱深度为25 dB的LPFG,并采用该光栅搭建了FBG解调装置,将FBG粘贴于金属应变片表面,测试了其静态与动态响应特征。实验结果表明:该方法制作简单,成本低,具有较好的线性动态范围,可以实现较高灵敏度的FBG解调。     

Development of a multiwavelength Raman fiber laser based on phase-shifted fiber Bragg gratings for long-distance remote-sensing applications

We propose a simple and flexible multiwavelength Raman fiber laser based on phase-shifted fiber Bragg gratings (FBGs) and a tunable chirped FBG. Using a simple multiwavelength Raman laser configuration with a single phase-shifted FBG and a tunable chirped FBG, we readily achieved simultaneous two-channel sensing probes with a high extinction ratio of more than 50 dB over a 50-km distance. The multiwavelength output was stable and the peak fluctuation was less than 0.5 dB. The temperature and strain sensitivities are estimated to be 10.1 pm/degrees C and 7.5 pm/microstrain, respectively.     

光纤布拉格光栅的应变传感实验的研究

针对光纤布拉格光栅的应变特性进行了实验研究,利用计算机采集和处理数据.实验结果表明,Bragg波长随纵向应变的变化呈现出良好的线性,与理论分析结果一致;光栅的涂敷材料不会改变它的线性,但会引起光栅的应变灵敏度变化.     

Dependence of temperature and strain coefficients on fiber grating type and its application to simultaneous temperature and strain measurement

We report an investigation of the dependence of the temperature and strain coefficients on the grating type for fiber Bragg gratings that are UV inscribed in B/Ge-codoped fiber with and without hydrogenation. The results reveal that all types of grating exhibit similar strain sensitivities but markedly different temperature sensitivities, greater for gratings inscribed in hydrogen-free rather than hydrogenated fiber and substantially less in type IA gratings than all others. The sensitivity characteristics of these gratings have been used to implement a new type of dual-grating sensor for simultaneous measurement of temperature and strain that has properties superior to those of previously reported structures.     

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.     

Experimental verification of response of embedded optical fiber Bragg grating sensors in non-homogeneous strain fields

One of the advantages of optical fiber sensors is their ease of embedment within a structure for non-destructive strain monitoring. In particular, Bragg grating sensors are written directly into an optical fiber hence remaining unobtrusive. In addition, several gratings can be written in series along a single fiber, permitting sensing at discrete points throughout the strain field. However, in regions of strong strain gradients, measuring the strain at discrete points may not be sufficient. One solution is to write a Bragg grating longer than the strain region of interest and use the change in its spectral response to determine the applied strain field as a function of position along the fiber. This paper presents an experimental verification of the response of an embedded optical fiber Bragg grating (OFBG) to applied non-homogeneous strain fields. Optical fiber Bragg grating sensors were embedded in four epoxy specimens of different forms so as to apply known strain functions along the gauge length when the specimen is under uniaxial tension. The complete spectral response of the Bragg gratings was then measured as a function of increasing load. The results are compared with analytical calculations, based on the piecewise-uniform period assumption for chirped gratings. Finally, the use of these spectra is discussed as possible basis functions for the resolution of an arbitrary applied strain distribution.     

光纤Bragg光栅应变、温度交叉敏感问题的研究

解决应变和温度的交叉敏感,实现应变和温度同时测量一直是光纤光栅传感器研究的关键问题。从应变和温度交叉敏感的物理机制出发,较为全面地介绍了几种主要解决方案：双波长矩阵法、2个包层直径不同的FBG法、啁啾光栅法等。并且基于双波长矩阵法,提出了一种基于管式弹性应变敏感元件的光纤光栅传感器结构,很好地实现了温度150℃,压力20MPa的同时区分测量,其温度灵敏度为0.02nm/℃。解决了温度和应变同时区分测量这一技术难题。