Fiber-optic temperature sensor using low-coherence interferometry

Low-coherence interferometric sensors are an important group of optical fibre sensors. Combining high measurement resolution with broad measurement range, these sensors can measure accurately several physical quantities e.g. temperature. In this article we present the fiber-optic temperature sensor using low-coherent interferometry, which has been designed and elaborated.     

A fiber-optic voltage sensor based on macrobending structure

We propose and demonstrate an optical voltage sensing scheme based on a macrobending optical fiber in a ratiometric power measurement system. This novel approach to sensing has not been utilized before and has the advantage that the sensor involves simple fabrication compared to existing fiber-optic voltage sensors. To prove the feasibility of such a fiber-optic sensor, a sensor for a voltage range from 0∼100 V is demonstrated, with a resolution of 0.5 V. The sensor is robust, linear, and shows a competitive measurement resolution. The sensor can be easily scaled to suit other voltage levels and be effectively combined with optical current sensors.     

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.     

双参量偏振调制光纤传感器输出信号的分离与线性化

分析了用一个传感头实现双参量测量的偏振调制光纤传感器的工作原理，表明该传感器能同时输出两路信号，其中一路利用泡克耳斯效应测电压或利用光弹效应测压力，另一种利用旋光效应测温度。但其输出的两个测量参量之间存在交叉敏感现象，并且其输出呈明显的非线性。因此提出一种基于人工神经网络的双参量偏振调制光纤传感器输出信号分离与线性化方法。以传感器输出作为输入样本，测量参量的实际值作为输出样本，通过训练使神经网络建立传感器输出与其实际感受的测量值之间的复杂非线性关系。计算机仿真与实验结果表明，该方法不仅能在较宽的测量范围内有效地分离两个测量参量，而且能在神经网络的输出端得到理想的线性输出。     

Intensity measurement based temperature-independent strain sensor using a highly birefringent photonic crystal fiber loop mirror

A fiber-optic strain sensor is demonstrated by using a short length of highly birefringent photonic crystal fiber (HiBi-PCF) as the sensing element inserted in a fiber loop mirror (FLM). Due to the ultralow thermal sensitivity of the HiBi-PCF, the proposed strain sensor is inherently insensitive to temperature. When a distributed-feedback (DFB) laser passes through the FLM, the output power is only affected by the transmission spectral change of the FLM caused by the strain applied on the HiBi-PCF. Based on intensity measurement, an optical power meter is adequate to deduce the strain information and an expensive optical spectrum analyzer (OSA) would not be needed.     

Temperature sensor based on etched optical fiber with a metal coating

Presented in this work is a new class of optical fiber temperature sensor, of which the heat-expansion thin film is coated on the etched fiber. It uses the method that combine thermal carving technique with chemical etching. The sensitivity of the sensor is increased and the shape size is decreased. This sensor possesses the linear temperature response and the good repeatability. These sensors can be used to measure finely the temperature which is lower than 200°c.     

Measurement performance of an optical CCD-based pyrometer system

The measurement performance of a CCD-based pyrometer system using a three-color method was evaluated for scientific and engineering metrology. The relationships between the system parameters (exposure time and sensor gain) and the intensity measurements in an integrating sphere experiment were determined for a specific CCD sensor. The pyrometer system uses the three-color method based on the intensity ratio without geometry calibrations. The field measurement characteristics and the effectiveness of coupling the three-color channels were investigated in terms of the temperature measurement uniformity, temperature sensitivity and temperature range of the pyrometer system in standard blackbody tests. The results showed that the temperature non-uniformity is not proportional to the intensity non-uniformity and is in the range of 0.13-2.14%. The relative temperature sensitivities of intensity ratios for different channel combinations are different, which may provide a way to improve the measurement results. The temperature range bandwidth for object with a non-uniform temperature distribution varies from 190 to 270 K for this specific CCD-based pyrometer. The performance evaluation conclusions for the system with this specific CCD sensor are general and applicable for pyrometer systems using other CCD sensors.     

Signal-processing algorithm for white-light optical fiber extrinsic Fabry-Perot interferometric sensors

We present a novel signal-processing algorithm for single-mode optical fiber extrinsic Fabry-Perot interferometric sensors that can achieve both high-resolution, absolute measurement of the cavity length and a large dynamic measurement range simultaneously. The algorithm is based on an accurate model of the characteristics of a fiber-optic sensor that takes into account the phase shift that is due to the coupling of light reflected at the second surface to the lead-in fiber end.     

新型光纤光栅水声传感器的研究

提出了一种新型的光纤布拉格光栅(FBG)水声传感探头结构以及光纤光栅传感信号的自解调方法。利用一对匹配光栅构成推挽结构,实现了传感-解调的合二为一,大大地减小了系统的复杂度;并通过筒状弹性体结构,解决了裸光纤光栅测量水声信号的灵敏度过小的问题,并具有温度补偿作用。仿真与初步实验结果表明,该水听器探头的测量动态范围超过100 dB,在100~200 dB re 1μPa的水声压范围内,测量灵敏度为0.36 nm/Mpa。     

Simplified Formula of Bending Loss for Optical Fiber Sensors

A simple fiber-optic bending loss formula is achieved for optical fiber sensors. This simple formula considers various bending radii, number of turns, extra bending angle, and wavelength and has good agreement with theoretical and experimental data. We also propose a simplified formula for sensitivity of the fiber-optic bending loss in this article. The defined sensitivity formula has the benefit of showing parameters for fiber-optic bending sensor systems.     

Simplified Formula of Bending Loss for Optical Fiber Sensors

A simple fiber-optic bending loss formula is achieved for optical fiber sensors. This simple formula considers various bending radii, number of turns, extra bending angle, and wavelength and has good agreement with theoretical and experimental data. We also propose a simplified formula for sensitivity of the fiber-optic bending loss in this article. The defined sensitivity formula has the benefit of showing parameters for fiber-optic bending sensor systems.     

Infrared radiation thermometer using a silver halide optical fiber for thermal ablation

In this study, we have fabricated non-contact temperature sensor using an infrared optical fiber for measuring temperature distributions during radiofrequency ablation. We have measured an infrared radiation, which is transferred by a silver halide optical fiber from the multi-points on the water around inserted electrode, using a thermopile sensor and the output voltages of a thermopile sensor are compared with those of the thermocouple recorder. Also, the relationship between the temperatures and the output voltages of a thermopile sensor at the measuring points is determined to obtain the temperature distribution. The measurable temperature range of a fiber-optic non-contact temperature sensor is from 37 to 80 °C.     

Fiber-optic dielectric multilayer temperature sensor: in situ measurement in vitreous during Er:YAG laser irradiation

A fiber-optic instrument for temperature measurement is presented. The sensing element consists of an optical dielectric multilayer system acting as a micro-interferometer which is deposited on a single-mode fiber tip. The sensitivity of the implemented system is theoretically derived and experimentally determined by a calibration measurement. The small size of the probe makes the system well-suited, for instance, for endoscopic in vitro and in vivo measurements in medical applications, especially in small samples. The sensor is used for the investigation of the transient thermal behavior of vitreous during Er:YAG laser irradiation in order to study the local thermal effects that are important to minimize the potential for unintentional injury in laser vitrectomy and laser vitreoretinal surgery.     

基于Mach-Zehnder干涉仪的单模光纤声波传感器的研究

光纤传感器是20世纪70年代中期发展起来的一种新型传感器.它与普通的传感器相比,具有灵敏度高、抗电磁干扰、耐腐蚀、防燃等优点,因此在温度、应力、磁场等传感领域都有着广泛的应用.本文研究的光纤声波传感器,其基础为Mach-Zehnder(M-Z)全光纤干涉仪,我们主要的工作集中在传感臂探头的制作.所研制的基于M-Z干涉仪...     

基于无芯光纤的多参数测量传感器

设计并制作了一种基于单模-无芯-单模-无芯-单模光纤结构的马赫-曾德尔传感器,可用来同时测量折射率和温度.该传感器中,两处无芯光纤充当输入、输出耦合器,中间单模光纤作为传感臂.利用有限元仿真和理论分析,确定耦合器和传感臂的最优长度为15 mm.在无芯光纤中激发出的高阶模进入单模光纤的包层传输,由于倏逝场的作用,受到环境折射率和温度的影响.选取透射谱不同干涉级次的波谷作为研究对象,实现了折射率和温度的同步测量.实验结果表明:1545 nm附近干涉谷的折射率和温度灵敏度分别为–153.89 nm/RIU(refractive index unit)和0.166 nm/℃;1570 nm附近干涉谷的折射率和温度灵敏度分别为–202.74 nm/RIU和0.183 nm/℃.该传感器在实现折射率和温度同步测量的同时,仍能保持较高灵敏度,在生物医疗等方面有着较好的应用前景.     

Fiber sensor based on Lophine sensitive layer for nitrate detection in drinking water

A new characterization of Lophine as a sensitive layer to measure Nitrate in drinking water is presented in this paper. The characterization was performed with a standard slide and a standard multimode fiber coated with a Lophine sensitive layer (2,4,5-Triphenylimidazol (C₂₁H₁₆N₂)). Spectral characterization has been conducted in the wavelength range from 300 to 1100 nm. We have demonstrated that Lophine can be used as a fiber sensor for the detection of Nitrate in drinking water. The sensing properties of the fiber sensor were analyzed at room temperature. Successful results were achieved when sensing Nitrate in the range between 1 mg/l and 70 mg/l. The response time was 20 ms and the recovery time was 40 ms.     

Erbium-doped fiber ring laser sensor for high temperature measurements based on a regenerated fiber Bragg grating

This article presents an erbium-doped fiber ring laser for high temperature measurement with high accuracy. The proposed laser sensor employs a regenerated fiber Bragg grating (RFBG) as a sensor element. Through thermal treatments, the RFBG with enhanced thermal resistance was obtained. The laser emission optical spectrum presents good performance with a high optical signal-to-noise ratio of 58dB. Experimental results demonstrate a wavelength sensitivity to the temperature is 15.5 pm/ºC with the temperature range from 300ºC to 900ºC, and the correlation coefficient is 0.999. The results prove it is able to provide potential applications in high temperature measurement.     

Fiber-optic sensor based on evanescent wave absorbance around 2.7 μm for determining water content in polar organic solvents

The feasibility of sapphire fiber-optic sensors based on evanescent wave absorption spectroscopy in the infrared range for quantitative determination of water content in polar organic solvents has been investigated. Evanescent wave absorption spectra of sapphire fiber-optic sensors in glycerol, ethanol, and glycol with different water concentrations obtained and analyzed, respectively. Evanescent absorbance of the sensors in those organic solvents has been utilized to implement for in situ monitoring water concentration in organic solvents. The evanescent absorbance of sensors in glycerol and glycol has been found to vary linearly with water content in the range 0–30 % and in ethanol in the range 0–10 %, respectively. The fiber-optic sensors based on evanescent absorbance for monitoring water concentrations in those organic solvents are acceptably accurate, cost-effective, and reliable. Some methods to improve the accuracy of predicated water content in those organic solvents are also suggested. Overall, the results demonstrate that the sapphire fiber-optic sensor based on evanescent absorption spectroscopy is a promising candidate for prediction of water content in polar organic solvents in on-line and remote situation.     

激光加工微型光纤折射率传感器的工艺与特性

提出一种由157 nm激光制造的新型微型光纤法布里-珀罗折射率传感器的制作方法,传感头由靠近单模光纤端的具有光纤顶端微通道的法布里-珀罗空气腔组成,将单模光纤顶端的微通道作为检测介质的入口.分别在珐珀腔的反射界面镀以薄膜作为反射镜面来确保高的光对比度.试验中获得了1 130.887 nm/refractive-index的分辨率.和其他的光纤传感器相比,这种传感器具有体积小,结构坚固,高分辨率,线性良好,测量范围宽等优点,能够满足实际应用的要求,特别是对需要小型传感器的场合.     

Optical cavity coupled surface plasmon resonance sensing for enhanced sensitivity

A surface plasmon resonance (SPR) sensing system based on the optical cavity enhanced detection tech-nique is experimentally demonstrated. A fiber-optic laser cavity is built with a SPR sensor inside. By measuring the laser output power when the cavity is biased near the threshold point, the sensitivity, defined as the dependence of the output optical intensity on the sample variations, can be increased by about one order of magnitude compared to that of the SPR sensor alone under the intensity interrogation scheme. This could facilitate ultra-high sensitivity SPR biosensing applications. Further system miniaturization is possible by using integrated optical components and waveguide SPR sensors.