Hybrid fiber Bragg grating sensor for vibration and temperature monitoring of a train bearing

We report a fiber Bragg grating(FBG)-based sensor for the simultaneous measurement of a train bearing's vibration and temperature. A pre-stretched optical fiber with an FBG and a mass is designed for axial vibration sensing. Another multiplexed FBG is embedded in a selected copper-based alloy with a high thermal expansion to detect temperature. Experiments show that the sensor possesses a high resonant frequency of 970 Hz, an acceleration sensitivity of 27.28 pm/g, and a high temperature sensitivity of 35.165 pm/℃. A resonant excitation test is also carried out that demonstrates the robustness and reliability of the sensor.     

Temperature-Insensitive Fibre-Optic Acceleration Sensor Based on Intensity-Referenced Fibre Bragg Gratings

A temperature-insensitive acceleration sensor using two fibre Bragg gratings （FBGs）, based on reflection spectrum intensity modulation and optical power detection, is proposed and demonstrated. A cantilever beam is used to generate acceleration-induced axial strain along two sensing gratings, which are glued on the two opposite surfaces of the beam. Because the two gratings operate within the linear spectral range of a light source, formed by a thermally-tunable extrinsic Fabry-Perot optical filter, the intensity difference of the two reflections from the gratings is proportional to the acceleration applied. This eliminates the need for sophisticated wavelength interrogation of the gratings, and it also endows the sensor with immunity to temperature variation. Compared with a commercial micromachined accelerometer, the sensor is proven to be capable of accurately detecting acceleration.     

Application of high-precision temperature-controlled FBG filter and light source self-calibration technique in the BOTDR sensor system

A high-precision temperature-controlled narrow band-stop fiber Bragg grating(FBG) filter and light source self-calibration technique are proposed for application in the Brillouin optical time domain reflectometer (BOTDR) sensor system.With the proposed application,the BOTDR sensor system maintains good long-term stability and temperature precision through the reduction of the center wavelength drift in the FBG filters and corresponding decrease in the changes in light intensity.The experiment result shows that temperature precision of 1℃and temperature stability of 0.7℃can be achieved in a temperature sensor over a range of 8 km.     

A Distributed Fibre Bragg Grating Sensor Interrogator Employing a Reformative Arrayed Waveguide Grating

We present an interrogating technique employing a reformative arrayed waveguide grating without output waveguides in combination with a linear charge coupled device. A simple and effective data processing method called area equalized point is used to improve the system resolution. The simulation results show that the wavelength shift of a fibre Bragg grating with temperature can be precisely measured by this interrogation technique. The temperature accuracy and wavelength resolution of the sensor system are smaller than 0.08℃ and 0.8pm, respectively. If the FBG 3dB-bandwidth is 0.2nm with the wavelength spacing between two adjacent FBGs of 1.4 nm, the temperature and wavelength errors caused by crosstalk are respectively 0.01℃ and 0. 1 pm.     

A high sensitive fiber Bragg grating strain sensor with automatic temperature compensation

A high sensitive fiber Bragg grating （FBG） strain sensor with automatic temperature compensation is demonstrated. FBG is axially linked with a stick and their free ends are fixed to the measured object. When the measured strain changes, the stick does not change in length, but the FBG does. When the temperature changes, the stick changes in length to pull the FBG to realize temperature compensation. In experiments, 1.45 times strain sensitivity of bare FBG with temperature compensation of less than 0.1 nm Bragg wavelength drift over 100 ℃ shift is achieved.     

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 °C 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.     

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.     

FP cavity and FBG cascaded optical fiber temperature and pressure sensor

A fiber Bragg grating(FBG) and Fabry–Perot(FP) cavity cascaded fiber sensing system was manufactured for temperature and pressure sensing. Temperature sensing as high as 175°C was performed by an FBG for the linear variation of an FBG wavelength with temperature. After the temperature was sensed, the demodulation system can find the original FP cavity length and its pressure and cavity length correlation coefficient; thus, the ambient pressure would be calculated. The sensing pressure can be as high as 100 MPa with a repeatability of 1/10,000 and high stability. This kind of fiber sensor has been used in the Shengli Oil Field.     

Demodulation of the multi-peak fiber Bragg grating sensor based on partial wavelength scan

Until now, a high-efficiency demodulation method for fiber Bragg grating(FBG) sensors has been a challenge.In this Letter, by employing multi-peak FBGs, an FBG sensor with a partial wavelength scan is proposed and initially demonstrated. By demodulating a near-symmetrical multi-peak FBG and an asymmetrical multi-peak FBG in the strain experiment, sensor sensitivities of 1.02 pm/με and 1.01 pm/με are measured for the interrogation system, respectively. The average demodulation deviations for the two sensors are 1.81% and 0.4%,respectively. The proposed method is expected to realize high-efficiency and low-cost FBG interrogators.     

Investigation on temperature characteristics of weak fiber Bragg gratings in a wide range

A weak fiber Bragg grating(WFBG) is an ideal quasi-distributed optical fiber sensor. Special attention should be paid to the spectrum and sensing performance of the WFBG at extreme temperatures due to its poor reflection intensity. In this Letter, the temperature characteristics of the WFBG from-252.75°C to 200.94°C are experimentally investigated. Five WFBGs with reflectivity from ~0.25% to ~10% are used in the experiments. The reflectivity variations and wavelength shifts at different temperatures are studied. Experimental results show that the WFBG can survive and work at extreme temperatures, but the performance is affected significantly.The reflectivity is affected significantly by both cryogenic temperature and high temperature. The temperature responses of Bragg wavelengths in the wide temperature range are also obtained.     

陶瓷封装对光纤光栅体温测量探头效果的影响

利用陶瓷封装技术,设计并制作了多只光纤光栅温度传感头,测试了探头的测试灵敏度、稳定性、重复性、响应速度等多个参数受封装加工形式的影响。实验采用恒温水浴装置,在36℃~45℃的温度范围内使用了中心波长位于1 540 nm和1 550 nm附近的多只布拉格光纤光栅进行了对比测量。实验结果表明:陶瓷封装布拉格光纤光栅的波长/温度响应度为9.815 pm/℃,测量标准偏差为0.08 ℃。     

合金钢封装光纤Bragg光栅传感器传感特性的研究

提出了一种光纤光栅新型合金钢封装结构。利用等强度悬臂梁和温度控制箱对合金钢封装光纤布拉格光栅的应力和温度传感特性进行了测量。实验表明,采用该种封装的光纤光栅传感器保持了裸光纤光栅的响应灵敏度,其拉应变灵敏度系数为1.17pm/με,压应变灵敏度系数为1.2pm/με,温度灵敏度系数为11.3pm/℃,线性响应度在0.9995以上,可满足实际应用的要求。     

具有温度自校准功能的光纤折射率传感器

提出一种具有温度自校准功能的光纤折射率（RI）传感器,传感头结构由2段很短的多模光纤（MMF）之间夹熔一段对折射率不敏感的光纤布拉格光栅（FBG）构成,传感头总长度为14 mm,FBG可以为折射率测量提供良好的温度校准功能。实验结果证明,该传感器的折射率灵敏度为126 nm。其干涉光谱共振波长的温度灵敏度为35.09 pm/℃,用于温度校准的FBG的温度灵敏度为11.14 pm/℃。相比于普通的折射率传感器,这种具有温度自校准功能的折射率传感器具有良好的实用前景。     

On a fiber grating sensor system with the capacity of cross-sensitivity discrimination

A novel fiber Bragg grating (FBG) sensor system based on an interrogating technique by two parallel matched gratings was designed and theoretically discussed. With an interrogation grating playing the role of temperature compensation grating simultaneously, the wavelength drifts induced by temperature and strain were discriminated. Additionally, the expressions of temperature and strain were deduced for our solution, and dual-value problem and cross sensitivity were solved synchronously through data processing. The influence of the FBG's parameters on the dynamic range and precision was discussed. Besides, the change of environment temperature cannot influence the dynamic range of the sensor system through temperature tuning. The system proposed in this paper will be of great significance to accelerate the real engineering applications of FBG sensing techniques.     

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。     

基于反射光谱特征辨识的光纤气压与温度集成监测方法

针对飞行器机载环境多参量综合测试需求,研究了一种基于反射光谱特征辨识的光纤布拉格光栅(FBG)气压与温度集成监测方法,给出了基于膜片式结构的双参量传感机理及其理论模型。采用基于耦合模理论的OptiGrating软件,得到不同气压与温度条件下光纤布拉格光栅传感器仿真反射光谱。在此基础上,借助弹塑性和恢复性能优良的平膜片感压机构,构建了膜片式双光纤气压/温度集成监测模型。研究表明,恒温条件下应变传感光纤光栅反射光谱随气压增加而逐渐向短波方向偏移,其中心波长灵敏度约为0.803 0 nm·MPa-1,且反射谱主峰及其旁瓣峰值均随气压变化呈现良好线性关系;当气压恒定而温度变化时,处于仅感温不受力状态的温度传感光纤光栅反射光谱中心波长灵敏度约为9.39 pm·℃-1;当气压与温度交叉变化时,能够实现对变温条件下的微小气压变化实时监测。传感光纤光栅受非均匀应变效应反射光谱存在一定啁啾现象,其反射光谱旁瓣峰值波长随环境温度、气压变化均会发生偏移,具有良好线性关系,且在不同气压下反射光谱对应的同一阶数旁瓣峰值幅度相等。该研究能够为航空航天器系统多物理参量在线综合测试提供有益帮助。     

基于光子集成芯片的可穿戴光纤光栅解调研究

为了实现光纤光栅传感器在可穿戴系统中的应用,提出了一种基于硅基光子集成芯片的可穿戴光纤光栅传感解调系统。基于比利时iSiPP50G工艺的光子集成芯片由4×1长波长VCSEL阵列、1×8阵列波导光栅、2×2 MMI耦合器、4×1光纤光栅耦合器阵列、Ge-on-Si波导光电探测器、直波导和弯曲波导等组成。在完成对VCSEL光源金线键合和光子集成芯片光纤耦合封装的基础上,设计了手环式解调电路,对人体温度和心音信号进行了实时测量。实验结果表明:解调系统的动态波长检测范围为1 540 nm～1 560 nm,波长分辨率为0.08 pm,解调精度为5 pm,温度监测范围为35℃～42℃,误差为±0.1℃;可检测50 Hz～100 Hz频率范围内的心音信号,可识别出第一心音和第二心音,并计算出心动周期、心率、第一心音时限、第二心音时限和心力等特征参数。     

基于光谱特征分析的光纤光栅腐蚀传感器研究

针对航空航天领域铝合金结构服役过程腐蚀监测需求,提出了一种基于铝质细管结构的预载荷型光纤光栅腐蚀传感器。给出了铝合金结构腐蚀在役监测机理,得到光纤光栅反射光谱特征与铝质细管厚度变化之间的理论关系模型,构建了酸碱环境下的光纤光栅腐蚀监测试验系统。通过在细管内部配置不受力且仅感受温度变化的光纤光栅传感器,解决了被测目标的温度与应力交叉敏感问题。研究表明,这种铝质细管封装设计不仅可以感受腐蚀对其力学性能的影响,还能够屏蔽外界腐蚀因素对管内光纤感知器件的干扰。随着金属管腐蚀程度加深,其管壁逐渐变薄,光纤光栅反射光谱逐渐向短波长方向偏移,且管壁厚度变化与光栅中心波长偏移量之间呈较好单调关系。这些特性能够为进一步开展基于光纤感知器件的机械结构在役腐蚀监测研究提供有益帮助。     

温度不敏感的光纤布拉格高压传感技术研究

 为了实现单一光纤光栅对压强精确测量,设计了一种温度不敏感的光纤布拉格高压传感器。对该传感器的温度特性及压强响应特性进行研究。给出了该传感器的结构及封装方法。从理论上分析了该传感器的温度去敏原理,推导了该压强传感器的光纤布拉格光栅中心波长与压强的关系,得到了该传感器的压强响应灵敏度的解析表达。通过实验分析传感器的温度特性及压强响应。实验结果表明,在21℃～260.8℃的范围内,实现了温度补偿,平均波长漂移量为0.75 pm/℃,在0～44 MPa的范围内,获得了-0.054 8 nm/MPa的压强响应灵敏度,是裸光纤布拉格光栅压力响应灵敏度的18.27倍。该传感器的压强响应具有很好的线性和重复性,实验值与理论值吻合得很好,该传感器能够通过一只光纤布拉格光栅实现压强的精确测量。     

利用双周期光纤光栅实现应变和温度同时测量

提出了一种新颖双周期光纤光栅传感器。在同一段氢载光纤上先后写入长周期光纤光栅、短周期布拉格光纤光栅 ,利用长周期光栅和布拉格光栅对应变和温度敏感性的差异 ,可实现应变和温度的同时测量。实验中采用这种灵敏结构的双周期光栅 ,在 0～ 170 0 με和 2 0℃～ 12 0℃范围内 ,测量精度可达到± 16 με和± 0 8℃。