带温度补偿的分布式光纤温度传感系统设计

针对分布式光纤温度传感系统(Distributed Optical Fiber Temperature Sensing System,DTS)在线测温精度不高的问题,提出了使用光纤布拉格光栅(Fiber Bragg Grating,FBG)解调仪对DTS进行温度补偿。对不带温度补偿的DTS进行了温度测量和数据分析,证明了进行温度补偿的必要性。设计了带温度补偿的DTS并进行了温度测试。实验结果表明,在使用FBG解调仪对DTS进行温度补偿后,DTS的温度精确度可以达到0.3℃。     

利用啁啾光纤光栅进行色散补偿的研究

分析了由于光纤的色散引起的脉冲展宽,并介绍了啁啾布拉格光纤光栅进行色散补偿的基本原理。２－５Ｇｂ／ｓ、１００ｋｍ 色散补偿的实验结果表明,利用啁啾光纤光栅进行色散补偿是一种切实可行的色散补偿方案。     

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.     

Relative humidity sensor with optical fiber Bragg gratings

A novel concept for an intrinsic relative humidity (RH) sensor that uses polyimide-recoated fiber Bragg gratings is presented. Tests in a controlled environment indicate that the sensor has a linear, reversible, and accurate response behavior at 10-90% RH and at 13-60 degrees C. The RH and temperature sensitivities were measured as a function of coating thickness, and the thermal and hygroscopic expansion coefficients of the polyimide coating were determined.     

Optimal design of temperature-insensitive long period fiber gratings for athermal refractive-index sensor

Based on coupled-mode theory of long-period fiber grating (LPFG), a theoretical analysis and simulations for the optimal design of a temperature-insensitive LPFG is presented in order to achieve an athermal condition for sensing the refractive index of the external medium. Effects of the variation of the cladding radius and grating period on the temperature sensitivity of the LPFG are discussed. Both of these parameters are found to be important to control the temperature sensitivity when the thermo-optic coefficients of core and cladding materials are of the same order. Other grating parameters are also optimized in order to achieve a good contrast of the grating period with resonance wavelength in the 1.5 μm region and to sense the external medium refractive index over a wide range. Variation of external medium refractive index from 1.0 to 1.45 results a red-shift in the LPFG resonance wavelength by 86 nm with its temperature sensitivity as low as 0.008 nm/°C over a temperature range of 0–80 °C for this optimally designed LPFG.     

Dual-channel microfluidic sensor based on side-hole fiber with two long-period fiber gratings

We propose and demonstrate a dual-channel microfluidic sensor based on a side-hole fiber(SHF)with two longperiod fiber grating(LPFG)structures.There are two air holes in the SHF,which are natural microfluidic channels.We fabricate two LPFGs(long-period gratings LPG-A and LPG-B)in the SHF with the resonance wavelengths of 1268.7 nm and 1385.8 nm,respectively.Results show that the refractive index sensitivities of LPG-A and LPG-B are?76.0 nm/RIU and?71.1 nm/RIU,respectively.One can measure the refractive index of liquid samples in two channels simultaneously.The proposed dual-channel microfluidic sensor has advantages of good linearity response,fluidic technology compatibility,and easy light input/output coupling and system integration,which helps the sensor to have a potential application in environmental detection and food safety detection.     

Strong phase-controlled fiber Bragg gratings for dispersion compensation

Dispersion-compensating fiber Bragg gratings with approximately 99.9% reflectivity that are made by continuous apodization and phase control are demonstrated. These strong dispersion-compensating gratings provide precision second-order, third-order, or even more complex dispersion compensation, as well as sufficient transmission isolation to be used at add-drop stages without additional filtering. A 99.84% grating with a constant approximately 700-ps/nm dispersion and a 99.94% grating with dispersion varying linearly from 1000 to -1000 ps/nm are demonstrated.     

Simultaneous temperature and bend sensing with long-period fiber gratings

Long-period gratings (LPG's) written in commercially available boron-codoped fibers operating at wavelengths of <1.1mum are shown to exhibit high temperature and bending sensitivities. Each resonant attenuation band of such LPG's was observed to split in two when the LPG's were bent. The split attenuation bands' separation increased significantly with increasing bend curvature, and the central wavelengths of the split bands provided a measure of temperature. We exploit this effect to allow for simultaneous measurement of temperature and bending in smart-structure applications. The demonstrated novel sensor system is simple and low cost.     

Low-noise and highly stable optical fiber temperature sensor using modified pulse-reference-based compensation technique

We modify the pulse-reference-based compensation technique and propose a low-noise and highly stable optical fiber temperature sensor based on a zinc telluride film-coated fiber tip. The system noise is measured to be 0.0005 dB, which makes it possible for the detection of the minor reflectivity change of the film at different temperatures. The temperature sensitivity is 0.0034 d B/℃, so the resolution can achieve 0.2℃. The maximum difference of the temperature output values of the sensor at 20℃ at different points in time is 0.39℃. The low cost, ultra-small size, high stability, and good repeatability of the sensor make it a promising temperature sensing device for practical application.     

Optimal design and fabrication of SMS fiber temperature sensor for liquid

Single-mode/multi-mode/single-mode (SMS) fiber sensors are optimally designed and used as high sensitivity temperature sensors in special temperature range. It is shown that the width of multi-mode fiber is a key factor influencing the performance of as-fabricated temperature sensors, which can be effectively controlled in the fabrication process by monitoring the output power of SMS fiber during wet acid etching process. As-fabricated temperature sensors show promising potential applications for precisely monitoring chemical reaction temperature in chemistry and biomedicine fields.     

Optimal design of short fiber Bragg gratings with triangular spectrum

Based on the mutated adaptive quantum-behaved particle swarm optimization (MAQPSO) algorithm and the discrete layer peeling (DLP) algorithm, we propose a method to design triangular-spectrum fiber Bragg gratings (TS-FBGs). In this method, the DLP algorithm is used to generate an appropriate initial range of the index modulation, and the MAQPSO technique is applied to optimize the index modulation within this range. The quantum-behaved particle swarm optimization algorithm with mutation operation can improve the search performance of this algorithm. We purposely use a linear weighting factor for the fitness value function in view of the linear edge triangular-spectrum. This dramatically accelerates the convergence in the numerical implementation. Using the proposed method, a 0.2 nm bandwidth TS-FBG is designed and the performance is shown to be better than previously reported results in the literature. Then, a 2.5 nm bandwidth TS-FBG is reconstructed; it is indicated that a short grating length can be used to realize the TS-FBG with chirp-free structure so that complex phase modulation is avoided in fabrication. Finally, a triple-channel TS-FBG with sampled-free structure is successfully designed and optimized. We also present an analysis on the tolerance of the design method over possible fabrication error.     

Simultaneous strain and temperature sensor based on the numerical reconstruction of polarization maintaining fiber Bragg gratings

When a short-length fiber Bragg grating is inscribed into a polarization-maintaining fiber, the resonant peaks produced by birefringence can overlap. In this case, the discrimination between strain and temperature effects is only possible by means of polarization control devices, i.e. a linear polarizer and a polarization controller. To avoid this complexity and the measurement errors that it involves, we propose a novel demodulation technique based on the numerical reconstruction of the grating physical parameters. Our technique evaluates the grating parameters from the amplitude spectrum by means of the coupled-mode equations. The convergence tool used to search the solutions is the Nelder–Mead simplex algorithm. The method is tested on uniform and apodized Bragg gratings and a very good accuracy is reported. The method is finally applied to a 2 mm-long uniform polarization-maintaining grating in order to simultaneously measure longitudinal strain and temperature.     

Intrinsic fiber Fabry-Perot temperature sensor with fiber Bragg grating mirrors

A fiber Fabry-Perot interferometer (FFPI) sensor is formed with broadband (~3 nm, 3-dB bandwidth) fiber Bragg grating (FBG) mirrors. Repetitively modulating a distributed-feedback laser produces chirping that modulates the reflectance of the FFPI. Because the reflectance of the FBG mirrors varies with optical frequency, the fringes in the sensor reflectance modulation are distinguishable, making it possible to extend the sensor dynamic range versus that of a FFPI sensor with conventional wavelength-dependent mirrors. An ambient temperature is determined in the range from 25 to 170 degrees C with a resolution of 0.005 degrees C.     

Dispersion compensation in transmission using uniform long period fiber gratings

It is proposed that the high dispersion at the transmission band edges of uniform long period gratings (LPG) fabricated on relatively high Δ fibers can be used for efficient dispersion compensation. Since the transmission of LPG varies with length of the grating or refractive index modulation, we show that it is possible to tailor the transmission spectrum to obtain high transmission with constant dispersion and negligible delay ripple over a reasonable bandwidth. Since the proposed structure works in transmission it should be suitable for fiber optic communication links.     

霍尔传感器温度漂移补偿电路设计

霍尔传感器作为一种半导体器件,其灵敏度随着温度变化而产生漂移的特性,限制了其在高精度磁场测量场合的应用。传统的温度补偿方法虽然对温度变化的一次项进行了完全补偿,但是却引入了温度变化二次项的误差。因此,对于温度变化显著的高精度测量场合,传统温度补偿法将不再适用。设计了一种闭环反馈电路,通过温度传感器采集温度信号,与信号处理电路的最终输出信号进行运算后送回信号处理电路的输入端进行补偿,而并不是简单地将温度信号与霍尔信号的输入信号进行相加后送入信号处理电路。仿真分析结果表明,通过调节补偿电路的反馈比例系数与霍尔芯片温度漂移系数,可以完全补偿霍尔芯片的灵敏度漂移。因此,这种闭环补偿方法可以不引入与温度变化二次项有关的误差,消除因温度变化产生的漂移,不仅适用于霍尔传感器,也适用于其他会随着温度漂移的传感器。     

霍尔传感器温度漂移补偿电路设计

霍尔传感器作为一种半导体器件,其灵敏度随着温度变化而产生漂移的特性,限制了其在高精度磁场测量场合的应用。传统的温度补偿方法虽然对温度变化的一次项进行了完全补偿,但是却引入了温度变化二次项的误差。因此,对于温度变化显著的高精度测量场合,传统温度补偿法将不再适用。设计了一种闭环反馈电路,通过温度传感器采集温度信号,与信号处理电路的最终输出信号进行运算后送回信号处理电路的输入端进行补偿,而并不是简单地将温度信号与霍尔信号的输入信号进行相加后送入信号处理电路。仿真分析结果表明,通过调节补偿电路的反馈比例系数与霍尔芯片温度漂移系数,可以完全补偿霍尔芯片的灵敏度漂移。因此,这种闭环补偿方法可以不引入与温度变化二次项有关的误差,消除因温度变化产生的漂移,不仅适用于霍尔传感器,也适用于其他会随着温度漂移的传感器。     

带光放大器的分布式光纤拉曼温度系统

 详细阐述了红外双波长带光放大器的分布式光纤拉曼温度系统原理,为了抑制放大器的自发辐射增长、温漂噪声积累、瑞利背向散射光窜扰反斯托克斯背向散射光,采用两条已知温度的曲线和最近测量温度曲线的解调方法,提高了系统的测温精度和稳定性并降低了系统的成本。实验结果与理论分析一致,系统的测温误差在±0.1 ℃内。     

高灵敏度光纤温度传感器

针对深井温度变化小,提出了一种可用于深井温度测量的高灵敏度光纤温度传感器。两根陶瓷插芯从铝管的两端插入构成外腔式光纤法珀干涉仪(EFPI)结构,用螺钉固定插芯,再用高强度的环氧树脂密封该结构,达到防水防尘效果。金属铝和陶瓷插芯具有不同的热膨胀系数,温度的变化将引起EFPI腔长变化,采用高灵敏度光纤白光干涉测量技术,就可以通过测量EFPI腔长获得被测温度。分别在固定温度和不同温度下,对腔长为146.5μm的EFPI光纤温度传感器进行了连续测量。测量结果表明,高灵敏度EFPI光纤温度传感器的腔长-温度灵敏度为260nm/℃,温度测量分辨率为0.002℃。     

线性啁啾光纤光栅色散补偿性能的数值分析

对线性啁啾光纤光栅的色散补偿性能进行了数值分析。结果表明 ,啁啾光栅时延曲线的纹波大小和线性度是影响其色散补偿性能的两个重要因素。对高斯型耦合系数分布光栅而言 ,更长的光栅将具有更佳的色散补偿性能     

带光放大器的分布式光纤拉曼温度系统

详细阐述了红外双波长带光放大器的分布式光纤拉曼温度系统原理,为了抑制放大器的自发辐射增长、温漂噪声积累、瑞利背向散射光窜扰反斯托克斯背向散射光,采用两条已知温度的曲线和最近测量温度曲线的解调方法,提高了系统的测温精度和稳定性并降低了系统的成本。实验结果与理论分析一致,系统的测温误差在±0.1 ℃内。