少模光纤倾斜光栅制备及扭转传感研究

设计了一种基于少模光纤倾斜布拉格光栅的反射型扭转传感器,小角度倾斜光栅中的纤芯基模与二阶模在光栅处发生互耦,通过测量该过程形成的反射峰强度变化实现扭转测量。分析了光栅倾斜角度对模式耦合效率的影响,采用相位掩模板法在线刻写光栅技术,在少模光纤上刻写了不同的小角度倾斜光栅;在此基础上选择倾斜角度为1°的光栅进行了单点、双点扭转传感实验,实验表明其反射光谱中基模与二阶模的互耦合峰(LP₀₁-LP₁₁)对光纤扭转敏感,可以实现对扭转角度大小的测量。在-50°～-150°逆时针扭转过程中,扭转灵敏度为0.52 dB/(rad·m^-1),而在40°～190°顺时针扭转的角度范围内,扭转灵敏度为0.34 dB/(rad·m^-1)。这种传感器具有在单根光纤上实现多点扭转传感的潜力,在多点扭转监测方面具有应用前景。     

AN OPTICAL FIBER TEMPERATURE SENSOR BASED ON AN ETHANOL FILLED FABRY-PEROT CAVITY

Optical fiber Fabry-Perot interferometers have been widely used as sensors. A novel anhydrous ethanol-filled optical fiber Fabry-Perot temperature sensor was reported in this article. Based on the characteristics of the temperature-controlling refractive index, the ethanol may serve as a sensitive medium for a sensor. According to the experimental results, the refractive index of the ethanol was changed by approximately 0.02617 when the temperature increased from 16°C to 74°C. A cavity length of 94 μm was used to demonstrate the feasibility of this sensor. The resonance wavelength of the sensor shifted about ?0.42 nm/°C. The novel optical fiber Fabry-Perot temperature sensor was simple, compact, sensitive, and immune to electromagnetic interferences.     

Temperature and refractive index sensor using a high-birefringence fiber loop mirror and single mode-coreless-single mode fiber structure

A novel fiber optic sensor for the simultaneous measurement of refractive index and temperature is reported. The sensor consists of a high-birefringence fiber loop mirror and a section of single mode-coreless-single mode fiber structure. The single mode-coreless-single mode fiber structure served as a refractometer while the high-birefringence fiber loop mirror was used to measure temperature. The multimode interference valley of the single mode-coreless-single mode fiber structure was sensitive to the surrounding refractive index of liquids (96.42 nm/refractive index unit) and had almost no response to temperature fluctuations. The high-birefringence fiber loop mirror was highly sensitive to temperature (1.98 nm/°C) but was insensitive to changes in refractive index. The theoretical and experimental results demonstrated simultaneous measurement of temperature and refractive index. The optimum resolution was 2.07 × 10^?4 refractive index units and 0.01°C.     

Sensitivity-enhanced single-mode fiber-tapered hollow core fiber-single-mode fiber Mach–Zehnder interferometer for refractive index measurements

In this paper, a sensitive-enhanced single-mode fiber—tapered hollow core fiber—single-mode fiber Mach–Zehnder interferometer is demonstrated for refractive index sensing. The sensitivity was improved by forming an up-taper at the two splicing joints and concave cone in hollow core fiber. The up-tapered regions served as a more effective mode splitter/combiner, and the tapered hollow core fiber was used to generate a stronger evanescent field to enhance the interaction of light with the analyte. According to the principles of interference between the cladding and fundamental modes, we performed refractive index measurements. The experiments indicated that the proposed sensor has a high refractive index sensitivity of 214.97?nm/RIU in the refractive index range of 1.333–1.379, with a minimum refractive index measurement resolution of 9.3?×?10^?5. In addition, the sensor had a low temperature response of 2.96?pm/°C in the range from 50 to 85°C and a low cross sensitivity of 1.377?×?10^?5 RIU/°C. The proposed sensor is attractive for its high refractive index sensitivity, easy fabrication, low cross sensitivity, and good mechanical strength, making it of potential value for refractive index measurements for chemical and biological sensing.     

Simultaneous measurement of humidity and temperature using a polyvinyl alcohol tapered fiber bragg grating

An optical fiber sensor based on a multimode tapered fiber cascading fiber Bragg grating has been proposed and experimentally demonstrated for the simultaneous measurement of humidity and temperature. The sensor was constructed using a tapered fiber that was coated with polyvinyl alcohol and a fiber Bragg grating with high reflectivity. The measurement of humidity and temperature was achieved by monitoring changes in reflective optical power and spectral shift, respectively. Due to the different measurement methods, the effect of temperature on humidity measurement may be ignored. The theoretical analysis and experimental results show that the highest sensitivities of 0.33 µW/%RH and 10.9?pm/°C were achieved when the diameter of the taper waist was 26?µm and the thickness of coating was 3.3?µm. Due to the advantages of good linearity, low cost of fabrication and convenient operation, the proposed sensor is promising for simultaneously measuring humidity and temperature.     

High sensitivity all-fiber Sagnac interferometer temperature sensor using a selective ethanol-filled photonic crystal fiber

An all-fiber Sagnac temperature sensor based on 3?dB tapered coupling and ethanol selective-filled photonic crystal fiber was demonstrated theoretically and experimentally. The ethanol selectivity-filled photonic crystal fiber has noncircular symmetry and thus exhibits birefringence. The ethanol selective-filled photonic crystal fiber, acting as the sensing element, was inserted in a Sagnac loop interferometer to measure temperature. The output spectra of Sagnac interferometer applied different temperatures were measured and analyzed. Experimental results have shown the temperature sensitivity of the Sagnac interferometer is 1.65?nm/°C in the range of 25–33°C.     

Optical Ring Resonator Based Temperature Sensor

Temperature sensor based on optical ring resonator has been demonstrated with its constituent material as silicon (Si-fiber) and germanium (Ge-fiber) in this work. It has been done through optical delay line signal processing technique in Z-domain. The group indices of both the materials vary with the change in temperature due to the thermo-optic effect in materials. Thus temperature dependence of free spectral range forms the basis of modeling the sensors. Silicon (Si) fiber based optical sensor can sense the temperature in the range 30–500 °C and that for germanium (Ge) fiber the range is ?25 to 300 °C. Obtained temperature sensitivities for Ge and Si-fibers are 5.55 and 2.97 MHz/°C respectively.     

High temperature and force measurements using a type II cascaded regenerated fiber Bragg grating (RFBG)

Abstract

A Type II-IR (infrared) grating cascaded with a regenerated fiber Bragg grating (RFBG) is described for force measurements at high temperature. The sensor was fabricated by fusion splicing a Type II grating with a Type I seed grating that was subjected to isothermal annealing in order to obtain the RFBG. Due to the different responses to temperature and force, these parameters were determined by measuring the reflection peak of the Type II grating and RFBG. The experimental results indicate that the sensor may be used for simultaneous measurement of temperature and force from 250?°C to 500?°C and 0.003?N to 0.797?N.     

Sensitivity-optimized long-period fiber gratings for refractive index and temperature sensing

A long-period fiber grating sensor was fabricated by periodically changing the structure of single-mode fiber with an electric arc discharge technique. After the fabrication, the refractive index and temperature sensitivities were optimized by etching the cladding with hydrofluoric acid solution. The experimental results illustrate that the thinner cladding shows relatively higher refractive index and temperature sensitivities for the same order cladding mode, which are accordant with that of numerical simulation. After the long-period fiber grating was etched for 15?min, average refractive index sensitivities of 214?nm/refractive index unit (RIU) (1.3333?–?1.3931) and 1987?nm/RIU (1.4115–1.4555) were achieved. An extremely higher refractive index sensitivity of 2731?nm/RIU appears near 1.4555. By systematically studying the temperature sensing characteristic of cladding-etched long-period fiber grating in this work for the first time, the temperature sensitivity can reach as high as 144.23?pm/°C when the ambient temperature changes from 30 to 80°C. This work provides a theoretical reference for the fabrication of a high-sensitivity refractive index and temperature sensor based on arc-induced long-period fiber grating.     

涡轮叶片三维叶尖间隙光纤检测系统

航空发动机涡轮叶片叶尖间隙呈三维变化特点,传统光纤式叶尖间隙检测系统的测量结果受维间耦合影响精度差,信息源单一。本文利用一种沿直角等腰三角排布的三路双圈同轴式光纤传感基元组成的传感探头,通过BP神经网络解耦方法,实现了从传感器输出到叶尖端面径向间隙、轴向倾角和周向倾角三维参量的解耦。设计加工三维测量光纤传感器和后续调理电路并对检测系统进行了静、动态实验验证。实验结果表明:该系统径向间隙静态测量的最大误差为47μm,标准差为10μm,轴向和周向倾角的静态测量最大误差分别为0.49°和2.32°,标准差分别为0.13°和0.36°。系统具有良好的重复性和可靠性,径向间隙的动态测量标准差小于18μm,轴向和周向倾角的动态测量标准差小0.2°和0.5°,能够满足航空发动机涡轮叶片叶尖间隙三维参量快速实时检测的需求。     

Simultaneous measurement of refractive index and temperature based on a long period fiber grating inscribed in a photonic crystal fiber with an electric-arc discharge

A novel fiber sensor composed by two single mode fibers and long period fiber grating based on a photonic crystal fiber prepared by periodic discharge heating has been experimentally investigated to measure refractive index and temperature. A Mach-Zehnder interferometer was formed due to the presence of two fusion spliced collapsed regions in the photonic crystal fiber. The resonance dip and interference pattern were differently influenced by the ambient disturbance, so the dual-parameters were simultaneously measured by analyzing the characteristics of transmission spectrum. After the experimental measurements, refractive index and temperature sensitivities of 117.28?nm/RIU and ?86.29?pm/°C were realized. Therefore, the reported sensor with advantages of easy fabrication, simple structure, and small size has the potential for simultaneous refractive index and temperature measurements involving biochemical sensing applications.     

Fiber optic temperature sensor using the orbital angular momentum and gaussian beams

A fiber optic temperature sensor is reported based on the interference between the orbital angular momentum and Gaussian beams. A Mach-Zehnder interferometer was employed to convert the temperature signal to a light signal of the phase difference between the reference and measuring paths. The fiber Bragg grating is included in the fiber of the measuring path. Different from the traditional sensing of fiber Bragg gratings by wavelength interrogation, the temperature-dependent phase delay near Bragg wavelength was utilized in this design. The resolution of system was better than 0.01°C. Moreover, the sensitivity of the system was obtained across various ranges of temperature. This system has potential applications in temperature measurements that require high resolution.     

基于LabVIEW的光纤布拉格光栅多节点应变监测技术

针对光纤光栅传感系统多节点有源地址查询技术,发展了一种基于LabVIEW软件平台的虚拟仪器,控制模拟电子开关各信道的导通时间,将来自传感光栅的脉冲信号按时序分配至各光纤光栅对应的输出信道,而且使开关动作与环行腔激光器中F-P滤波器的扫描同步。系统的测量范围为-672~672με,分辨力为5.9n,ε1540nm波长时系统传感灵敏度的实验值为1.57°/με,与理论值1.59°/με基本吻合。     

基于光纤传感技术的三维地应力传感器

为了实现对地下岩层空间应力状态及其变化规律的有效监测,基于光纤光栅传感技术与平面应力状态测量原理,提出了一种平面应变花与光纤光栅传感技术相结合的监测方法。通过利用碳纤维层积复合材料对光纤光栅封装做成应变传感单元,九个应变传感单元分别组成两组直角应变花与一组等角应变花,三组应变花分别放置于三个圆柱形探头S1,S2,S3上,三个探头以一定的机械结构连接构成地层空间应力的监测的三维地应力传感装置。对光纤应变传感单元进行温度与应力的标定实验,在室内对整体传感装置进行了应力加载模拟实验。实验结果表明:光纤应变传感单元的应力分辨率为0.017 2 MPa;应力监测为0~60 MPa;探头S1最大主应力的监测平均误差为16.31%,探头S2最大主应力的监测平均误差为24.36%,S3探头的绝对误差为0.006 8 MPa;实际加载应力与传感器测量的应力空间角度误差平均值为1.24°。传感器的监测结果与实际加载应力的变化规律相一致,可满足对地下岩层空间应力状态连续监测的要求。     

Refractive index sensor based on fiber loop ring-down spectroscopy

An optical fiber refractive index sensor based on fiber loop ring-down spectroscopy and a tapered fiber was fabricated using an ordinary single mode fiber with an arc fusion splicer. The performance of the sensor was controlled by the parameters of the tapered fiber. A fiber loop ring-down spectroscopy system was employed to enhance the sensitivity and demodulate the transmission spectrum. The results showed that a sensor with a waist diameter of 14 m and a length of 1.2 mm had good optical performance. By monitoring the ring-down time of the system, relatively high sensitivity of 411.576 s/ RIU was achieved with refractive index values from 1.333 to 1.412. This sensor offers few interferences, high sensitivity, easy fabrication, and low cost.     

Study on burr occurrence and surface integrity during slot milling of multidirectional and plain woven CFRPs

Machining carbon fiber reinforced composite (CFRP) is often accompanied with cutting edge defects and surface damage including interlayer delamination, cavities and debonding of fiber-matrix. A detailed understanding of the effect of fiber configuration and cutting parameters on cutting force, burr occurrence/formation and surface integrity is necessary. In this paper, experimental data is presented relating to fiber burrs on entry surface, cutting force, surface roughness and workpiece integrity when slot milling CFRP laminates with varying fiber configurations (0°/90°, 45°/135° and plain woven) at different cutting speed (60 and 120 m/min) and feed rate (0.05 and 0.1 mm/rev). Lateral cutting force is recorded down to 56 N and highly dependent on fiber orientation. The length (up to ~?5.6 mm) and amount of fiber burrs are highly related to fiber orientation and fiber cutting angle. Surface roughness Ra down to ~?1.4 μm was recorded when milling type 2 (45°/135°) and type 3 (plain woven) laminates. Various surface defects predominantly occurred due to different cutting conditions and fiber configurations, which are mainly located in the layers with fibers orientated at 45°/135°. The occurrence and propagation of fiber burrs and surface cavities were also investigated based on different fiber fracture mechanisms.     

A Fiber-Optic Microbending Temperature Sensor

A fiber-optic amplitude sensor based on the effect of microbending-caused upsetting of total internal reflection and intended for temperature monitoring is described. A measuring-system prototype was developed for investigating the sensor characteristics. The measured sensor characteristics show that a sensor with alcohol as the working fluid has a maximum sensitivity of 1.9 × 10^?2°C^?1. The range of linear variation of its normalized optical output signal was 0.829. The temperature range was 42.5°C, the maximum temperature being 74.5°C. It is shown that several sensors of this type can be integrated in fiber-optic lines to be used in distributed fiber-optic measuring networks.     

保偏光纤转轴熔接Sagnac干涉环的光学游标效应及温度传感器

为了实现高灵敏度的温度传感,通过在基于保偏光纤Sagnac干涉仪的Sagnac环内增加一段保偏光纤,控制两段保偏光纤快轴熔接角度接近45°,设计并制造了保偏光纤转轴熔接Sagnac干涉环结构。在理论上通过Jones矩阵推导了保偏光纤转轴熔接Sagnac干涉环的干涉谱公式,基于仿真分析研究了主要参数对保偏光纤转轴熔接Sagnac干涉环输出特性的影响。仿真结果表明,保偏光纤转轴熔接Sagnac干涉环实现了光学游标效应,两段保偏光纤的平均长度、两段保偏光纤的长度差分别影响保偏光纤转轴熔接Sagnac干涉环输出干涉谱的波长间隔和包络周期;在实验中,将保偏光纤转轴熔接Sagnac干涉环应用在光纤温度传感器中。实验结果表明,在2cm的感温区域,保偏光纤转轴熔接Sagnac干涉环温度传感器的灵敏度就达到了-2.44nm/℃,是普通Sagnac干涉环温度传感器(-0.163nm/℃)的14.97倍。     

Influence of fiber orientation on abrasive wear of unidirectionally reinforced carbon fiber–polyetherimide composites

A composite with continuous carbon fibers (CF) (80% by vol.) and high performance thermoplastic polyetherimide (PEI) matrix was developed and evaluated for various mechanical properties as a function of fiber orientation angle (0°, 30°, 45°, 60° and 90°). It was observed that Young's modulus, Poisson's ratio, toughness and % strain decreased with the increase of fiber orientation angle with respect to loading direction. In-plane shear modulus was highest for fibers with 45°. Overall, unidirectional (UD) CF reinforcement enhanced all strength properties of PEI significantly. Composites with fibers in 0° (parallel to loading direction) proved best in almost all the properties. Tribological evaluation in abrasive wear mode under different loads and fiber orientations indicated that coefficient of friction (μ) and specific wear rate (K₀) decreased with load, in general. Comparatively low specific wear rate (K₀), (in the order of 0.7 1×10^?9 m³/Nm) was observed for 0° fiber orientation, while fibers in 90° showed almost three times higher wear rate. Overall fiber reinforcement in 0° orientations proved beneficial from both strength and tribological performance point of view. SEM proved useful to correlate wear rate with surface topography.     

SIMULTANEOUS MEASUREMENT OF STRAIN AND TEMPERATURE WITH POLARIZATION MAINTAINING FIBER BRAGG GRATING LOOP MIRROR

□ A novel simultaneous method of strain and temperature measurement based on a polarization maintaining fiber Bragg grating loop mirror is proposed and demonstrated. The sensing head was composed of a fiber loop mirror and a section of fiber Bragg grating made of a polarization maintaining fiber. The Bragg wavelengths of the fiber grating in the polarization maintaining fiber were along slow and fast axis showing different sensitivities to strain and temperature with the interferometric peak wavelength of the fiber loop mirror. By monitoring the shifts of the Bragg wavelength and interferometric peak of the fiber loop mirror, with its temperature sensitivity of 0.1167 nm/°C and strain sensitivity of 0.0093 nm/μ?, a temperature measurement resolution about 0.009°C and a strain measurement resolution of 1.08 μ? was achieved theoretically and experimentally.