Long-period fiber grating sensor induced by electric-arc discharge for dual-parameter measurement

A long-period fiber grating sensor induced by electric-arc discharge has been fabricated and demonstrated for the simultaneous measurement of temperature and strain. The proposed sensor was fabricated by inscribing a sing-mode fiber with periodic electric-arc discharge technology that was produced from a commercial fusion splicer. The resonance dips formed by the coupling between cladding modes and core mode have different sensitivity responses, so the simultaneous measurement for multiple parameters was realized by monitoring the wavelength shifts of the resonance dips. Because of the easy fabrication and low cost, the sensor is promising for applications for which simultaneous measurement of temperature and strain is required.     

High sensitivity internal refractive index sensor based on a photonic crystal fiber long period grating

A high sensitivity method is reported for the measurement of the internal refractive index using a photonic crystal fiber long period grating. Long period gratings of different lengths were inscribed in photonic crystal fibers, and the air holes of the fiber had varying refractive indices. A side lobe appeared near the resonant dip through the analysis of the characteristics of transmission spectra showing variation in the refractive index. The resonant dip and its side lobe provided varying sensitivities to the internal refractive index values. The sensitivity of the side lobe was as high as 2343?nm/refractive index unit (RIU), which exceeded the value for the resonant dip (2047?nm/RIU) for refractive indices from 1.3333–1.3792. Due to the high resolution of 8.5?×?10^?6 RIU, this method offers promising applications for biological and chemical analysis in which high-precision refractive index measurements are required.     

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.     

Determination of refractive index by a U-shaped multimode fiber sensor

The U-shaped multimode fiber structure is proposed to measure the refractive index of liquid. In the previous work, the U-shaped structure by single-mode fiber has been widely investigated. However, the large bending loss restricted its practical applications, especially for the reflection-type fiber probe. To reduce the bending losses, the multimode fiber is used as the bending section of the fiber sensor in this study. The structures with different bending radiuses are fabricated to verify this design. Moreover, to simplify the interrogation method, the differential intensity interrogation method is used by cascading two fiber Bragg gratings after the U-shaped fiber structure. The low bending loss of the proposed structure is helpful to measure the reflected light power by fiber Bragg gratings. The influence of incident light power fluctuation was largely suppressed by this differential method. In addition, the sensitivity is also increased by a factor of 2 compared with the intensity interrogation method using one-cascaded fiber Bragg grating. The experimental results show that the refractive index sensitivities are ?115.09?dB/RIU in the refractive index range of 1.3405–1.3874 and ?260.24?dB/RIU in the refractive index range of 1.3874–1.4223, respectively.     

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.     

用于温度测试的光纤SPR传感器特性研究

表面等离子体波共振效应（SPR）对液体折射率变化非常敏感，而温度变化又会导致液体折射率和金膜复介电常数的改变。利用这一原理，可以考察温度变化对SPR共振效果的影响。采用相对光谱检测技术，获得相应的SPR反射光谱，并详细分析了共振波长和共振强度等参数随温度变化的特性曲线。定义耦合系数η，还可实现对不同液体温度下共振效应强度的评估。通过这些研究，进一步扩展了此类传感器的应用领域。     

基于光纤马赫泽德干涉的折射率测量

为了高精度的检测液体折射率,本文研究了基于模间干涉的马赫泽德光纤折射率传感器.传感器由普通的单模光纤和多模光纤组成,按照单模,多模,单模依次熔接在一起,并将熔接后的光纤进行拉锥处理,最终得到直径为10μm左右的传感头.实验结果表明,液体折射率在1.33到1.35范围内增大时,其透射谱的损耗峰将向长波方向移动.     

Theoretical analysis for the influence of the core radius on long period fiber grating sensors

Abstract

The influence of core radius on refractive index sensitivity of long period fiber grating (LPFG) sensor has been studied theoretically for the first time, and a new method to fabricate LPFG sensor with high sensitivity is proposed. The structure and parameters of the optical fiber, the period of the gratings, and the coupling order of the cladding modes are all held consistent in the process of studying the change of the core radius. The resonant wavelength of LPFG sensor shifts with changes in the external environment, which is simulated by the transfer matrix method. The sensitivity of LPFG sensor is enhanced by more than 200 times when the core radius increases from 3.1 to 5.1?μm. The results show that LPFG sensors with larger core radii have higher sensitivity. Selecting a fiber with a large core radius to fabricate LPFG sensors is proposed as a method to improve the sensitivity of these devices. This new simple and effective method is expected to be widely used in the manufacture of high sensitivity LPFG sensors in the future.     

塑料光纤折射率计连续测量研究

本文对基于宏弯曲塑料光纤的折射率计的连续测量特性进行了研究.宏弯曲结构的曲率半径与光纤半径的比值决定了该折射率计的工作特性.由于聚合物材料具有一定的吸水性,导致该折射率计在连续工作时其结构参数发生改变.实验表明,浸没时间超过40 h,折射率计产生了7.3×10-5 RIU的测量偏差.这项研究指出,基于塑料光纤的液体传感器,在连续工作时必须对其吸水性问题加以考虑.     

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.     

一种光纤光栅传感实验仪的可靠性分析

光纤光栅作为一种传感单元可以测试应变、温度和压力等物理量.近年来,可用于光纤光栅信号解调的技术和仪器相继出现,并在不同的场合得到了很好的应用.但由于制造、安装和操作等原因,这些仪器的可靠性问题也开始引起不同程度的关注.仪器的可靠性分析是其设计过程中不可缺少的重要环节之一.以一种基于匹配解调技术的准分布式光纤光栅解调仪为例,介绍了该仪器的基本组成和原理;采用故障树法从机械和光电器件的可能出现的如光纤光栅脆断、螺钉松动和脱焊等故障和失效形式出发,根据光路配置、电路以及机械结构分析了可能的故障模式,计算了可靠性.结论有利于对这类仪器的故障诊断和维护.     

温度和应力迟滞自补偿型光纤光栅传感器的研究

采用四对称悬臂梁与光纤布拉格光栅传感机构的组合设计，将2个相同反射波长的光纤光栅对称粘接于悬臂梁的上下表面，组成光栅串，实现对外压力的双光栅波长差的调谐方法。研究结果表明，该系统能自补偿光纤光栅压力传感系统的弹性迟滞影响，还能自补偿温度对光纤光栅压力传感的影响，解决了光纤光栅对压力和温度交叉敏感的问题，改善了传感系统的线性特性和重复性。在0～6MPa的测压范围内，双峰波长差的调谐范围为0—6．6nm，压力调谐双峰波长差的灵敏度可达1．12nm／MPa，在15—110℃测温范围内，温度调谐双峰波长的灵敏度可达0．028nm／℃。     

高灵敏度长周期光纤光栅温度传感器的设计

为提高光纤光栅温度传感器的灵敏度,文中采取纤芯弹光系数大于包层弹光系数的长周期光纤光栅且在其包层外面涂覆一层随温度的升高折射率减小的薄膜材料,同时采用热膨胀系数大的金属封装光栅三种增敏措施。计算表明,增敏后的温度传感器其灵敏度系数为0.2375nm/℃,温度测量分辨力小于0.1℃。     

Validation of thermal and electrical model for induction motors using fiber Bragg gratings

This works presents the simulation and validation of the thermal, electrical and mechanical models of a three-phase induction motor (TIM). Fiber Bragg grating (FBG) sensors are used to measure stator temperature and validate the thermal model. The knowledge of the relationship between losses and temperature variation in the TIM makes a simulation of the motor possible. To determine losses in the TIM an equivalent electrical circuit in arbitrary reference frame is used, which combines a traditional model with the more usual modeling of losses in the stator iron. The thermal study of the motor is performed using an equivalent thermal circuit formed by thermal capacitances and thermal conductivities that are separately considered for the stator and rotor. The losses calculated with the electrical and mechanical models are the input parameters for the thermal model. The simulation of the electrical model produces an error of approximately 4.2% when determining the Joule effect losses in the motor when compared to the experimentally obtained results. The simulation of the mechanical model presents an error of 0.2% for the losses due to friction and ventilation. The stator and rotor temperature, obtained with the thermal model, presented a high correlation with the measured values. The thermal model presents a maximum error of 0.75 °C when one compares them to the average experimental values of temperature in the stator during the temperature transient behavior. When the temperature in the stator reaches steady state, the experimental and simulated results converge to the same values. The use of FBGs to measure temperature in the machine allowed a thermal model to be developed, which also uses the mechanical losses of the machine and is the main contribution of this work.     

Small diameter fiber Bragg gratings and applications

Small diameter optical fibers are preferred in sensing systems as they have less influence on mechanical performance of smart composite. The static and dynamic monitoring capabilities of the small-diameter fiber Bragg gratings (FBG) are experimentally studied in this paper. Firstly, a small-diameter FBG is used as a strain sensor. Secondly, a temperature sensor is fabricated using a specific FBG. Thirdly, a simple sensing system is proposed in order to discriminate temperature at sensing point. Finally, utilization of these small diameter FBGs for vibration monitoring is discussed. The experiments revealed that the central wavelengths of the small-diameter fiber Bragg gratings shift linearly with strain or temperature. The FBG is more sensitive than a thermocouple inside the thermostat. Acquisition and analysis of the dynamic signal indicates that the designed FBG can be used for dynamic signal monitoring.     

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.     

光纤荧光温度传感器用于高压设备温度在线监测的研究

设计了一种基于荧光寿命的光纤温度传感器,用于高压开关柜触头温度的监测。采用稀土作为敏感材料,将其粘贴到被测体表面,实现了非接触测温。     

具有温度自补偿功能的新型光纤光栅应变传感器的研究

分析了光纤光栅的温度应变交叉敏感的机理,设计并制作了一种新型的具有温度补偿和应变增敏效果的光纤布拉格光栅应变传感器．实验结果表明,在-10-50℃的温度变化范围内,传感器实现了良好的温度补偿和应变增敏效果,温度敏感性降低至封装前的1／10,应变敏感性增至原来的1．17倍．