Nanocrystalline cerium oxide coated fiber optic gas sensor

A clad-modified fiber optic sensor with nanocrystalline CeO₂ is proposed for gas detection. As-prepared and annealed CeO₂ (500 °C) samples have been used as gas sensing media. The spectral characteristics of the fiber optic gas sensor are studied for various concentrations of ammonia, ethanol and methanol gases (0–500 ppm). The sensor exhibits linear variation in the spectral peak intensity with the gas concentration. The characteristics of the sensor are also studied for gas selectivity. The time response characteristics of the sensor are reported.     

Gas sensing property of lithium tetraborate clad modified fiber optic sensor

The micro structured plate-like lithium tetraborate, Li₂B₄O₇ (1 μm in diameter) has been prepared by sol–gel method and characterized structurally by X-ray diffraction and morphologically by scanning electron microscopy. UV–Vis spectrum shows about 60% transparency in the visible region and the optical energy band gap is found to be 3.5 eV which is also confirmed by strong near band edge emission from luminescence spectrum. The spectral characteristics of the cladding modified fiber optic sensor coated with microcrystalline Li₂B₄O₇ are studied for various concentrations of ethanol, methanol and ammonia (50–500 ppm). At 298 K, the sensitivity for ethanol is ?10 counts/ppm which is relatively higher than ammonia (?4 counts/ppm) and methanol (?3 counts/ppm). The time response of the sensor is presented for pure Li₂B₄O₇ with ethanol gas.     

Fiber-Optic Ammonia Sensors Utilizing Rectangular-Cladding Eccentric-Core Fiber

A new fiber-optic ammonia sensor utilizing rectangular-cladding eccentric-core fiber and a sensitive film containing an indicator dye is demonstrated. The sensitive film is a SiO₂-GeO₂ gel film including an indicator dye of bromocresol purple or bromocresol green, which is dip-coated by a sol-gel technique. The attenuation of this sensor changes depending on the concentration of ammonia at the wavelength range of 500–700 nm. This sensor can detect several ppm of gaseous ammonia. Various factors determining the sensitivity to detect the ammonia gas and time response of the sensor are also studied.     

Gas sensor using gold doped copper oxide nanostructured thin films as modified cladding fiber

We investigate the spectral response of nanostructured copper oxides thin film. Gold was doped in two different concentrations (2% and 4%) using the spray method. A novel ammonia gas sensor at various concentrations (0-500 ppm) was fabricated by replacing CuO films with a clad region. In addition, the effect of gold doping on structural, optical, and morphological properties has been demonstrated. The study shows that the spectral intensity increases linearly with ammonia concentration. The 4% Au doped CuO presents higher sensitivity compared with 2% doped and pure copper oxides. Time response characteristics of the sensor are also reported.     

ZnO thin film on side polished optical fiber for gas sensing applications

In this work, thin ZnO films have been produced by pulsed laser deposition on side-polished fiber for optical gas sensor applications. The influence was investigated of the processing parameters, such as substrate temperature and oxygen pressure applied during deposition, on the sensitivity to ammonia of the sensing element. A shift of the spectral position of the resonance minimum to the longer wavelengths was observed at room temperature for the sample prepared at 150 °C substrate temperature and 20 Pa oxygen pressure. Spectral changes in the range 0.16-1.13 nm for NH₃ concentrations between 500 and 5000 ppm were also observed.     

偏振模耦合分布式光纤传感器空间分辨率研究

分析了偏振模耦合原理的分布式光纤传感器的自相干与互相干光；实验测量的干涉光证明了理论分析是正确的；利用偏振模耦合原理传感与白光干涉检测的分布式光纤传感器的空间分辨率是由光纤偏振色散系数与光源的谱宽决定的；由实验测量的偏振模耦合分布式光纤传感器的空间分辨率为6cm. 关键词： 光纤传感器 保偏光纤 空间分辨率 偏振模耦合     

Determination of the thickness of a transparent plate using a reflective fiber optic displacement sensor

A fiber optic sensor for determining the thickness of a transparent plate (1–2.5 mm) is described based on a fiber optic displacement sensor. The sensor characteristics are found to vary with the change in the thickness of a plate. A theoretical model is proposed and validated with experimental results. The behavior of the sensor is evaluated and analyzed in terms of the numerical aperture and diameter of the fiber.     

基于光谱吸收型光纤传感器的煤矿瓦斯测量技术

甲烷是瓦斯的主要成分,是易燃易爆的气体。介绍了瓦斯的光谱特性以及光谱吸收法测量甲烷气体浓度的原理,给出了光谱吸收型光纤瓦斯气体传感器的主要进展和技术路径,包括差分吸收测量法和谐波吸收测量法。通过分析可看出,光谱吸收型光纤瓦斯传感器以其优良的特性得到了广泛关注,其中差分吸收法的抗干扰能力强,系统可靠性高,具有较强的工程应用价值。     

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。     

Ground vibrations detection with fiber optic sensor

In this paper, a fiber optic sensor based on fiber Bragg grating (FBG) is employed to measure the ground vibrations which may be generated by earthquakes, debris flows, landslides, and rock impacts on the ground. The detected vibration signals were analyzed by both fast Fourier transform (FFT) and Gabor transform to obtain the frequency response. The performance of fiber optic sensor was examined and compared with the conventional ground vibration geophone sensor. From the results of field tests, the fiber optic sensor shows highly similarity with conventional geophone sensor for low frequency measurement. The fiber optic vibration sensing system presented in this research is appropriate for sensing ground vibration in the frequency ranges of 10–250 Hz. The sensor proved to be an alternative option for ground vibrations monitoring system.     

基于自组装膜的光纤错位型氨气传感器

演示了一种基于单壁碳纳米管（SWCNTs）-聚合物自组装复合膜的光纤错位型氨气传感器。通过层层自组装技术在高Q谐振器上涂覆薄膜，薄膜上存在大量的游离羧基以及较大的比表面积，这提供了光与薄膜之间的强相互作用，以及对氨气的高吸附性和选择性。光谱随氨气浓度影响的有效折射率而变化。在(10～37) ×10?6的低浓度范围内，光谱变化与氨气浓度差之比即灵敏度为13.25 pm/10?6，检测极限为3.77 ×10?6并且具有良好的线性。这项工作研制为低浓度和高选择性氨气传感器提供了一种有效的方法。     

Fiber optic evanescent field sensor for detection of explosives and CO<Subscript>2</Subscript> dissolved in water

A fiber optic approach for the determination of the carbon dioxide concentration in the gas or fluid phase during sequestration, as well as for the sensing of the explosive TNT is described. The sensor consists of a quartz glass multimode fiber with core diameter of 200 μm and is based on the evanescent field principle. Cladding and jacket of the fiber are removed in the sensing portion, therefore interaction between light within the fiber and the surrounding medium is possible. A single-mode distributed feedback (DFB) laser diode with an emission wavelength around λ= 1.57 μm and a frequency doubled passively Q-switched Cr⁴⁺:Nd³⁺:YAG microchip laser (λ= 1064 nm)are used as light sources. The experimental setup and the sensitivity of the evanescent field sensor are characterized. PACS 42.62.Fi; 42.79.Wc; 07.07.Df     

Surface plasmon resonance based fiber optic sensor utilizing indium oxide

A highly sensitive surface plasmon resonance (SPR) based fiber optic sensor with indium oxide (In₂O₃) layer coated on the core of the optical fiber is presented and theoretically analyzed. The sensitivity of the SPR based fiber optic sensor has been evaluated numerically. It is shown that the proposed SPR based fiber optic sensor with In₂O₃ layer possesses high sensitivity in the near infrared region of spectrum, which needs attention to many environmental and security applications and offers more accurate and highly reproducible measurements. In addition, the sensitivity of the SPR based fiber optic sensor decreases with the increase in the thickness of In₂O₃ layer. With sensitivity as high as 4600 nm/RIU, the 170 nm thick In₂O₃ layer based fiber optic SPR sensor demonstrates better performance.     

Modeling and simulation of polarization errors in Sagnac fiber optic current sensor

Sagnac fiber optic current sensor (S-FOCS) is a kind of optical interferometer based on Sagnac structure, optical polarization states of sensing light wave in Sagnac fiber optic current sensor are limited. However, several factors induce optical polarization error, and non-ideal polarized light waves cause the interference signal crosstalk in sensor, including polarizer, quarter-wave retarder, splice angular, birefringence and so on. With these errors, linearly polarized light wave in PM fiber and circularly polarized light wave in sensing fiber become elliptically polarized light wave, then, nonreciprocal phase shift induced by magnetic field of the current is interrupted by wrong polarization state. To clarify characteristics of optical polarization error in fiber optic current sensor, we analyze the evolution process of random optical polarization state, linear optical polarization state and circular optical polarization state in Sagnac fiber optic current sensor by using Poincare sphere, then, build optical polarization error models by using Jones matrix. Based on models of polarization state in Sagnac fiber optic current sensor, we investigate the influence of several main error factors on optical polarization error characteristics theoretically, including extinction ratio in polarizer, phase delay in quarter-wave retarder, splice angular between quarter-wave retarder and polarization maintaining fiber. Finally, we simulate and quantify nonreciprocal phase shift to be detected in fiber optic current sensor related with optical polarization errors. In the end, we demonstrate S-FOCS in test. The results show that transfer matrix errors are induced by inaccurate polarization properties during polarization state conversion, then, the stability and accuracy of the S-FOCS are affected, and it is important to control the polarization properties at each step of the polarization state conversion precisely.     

Theoretical analysis of surface plasmon resonance based fiber optic sensor using indium nitride

An extremely sensitive surface plasmon resonance based fiber optic sensor with indium nitride (InN) layer coated on the core of the optical fiber is theoretically analyzed. The proposed sensor exhibits high sensitivity in the near infrared region of spectrum. The optimized value of thickness of InN layer is found to be 70 nm. Possessing high sensitivity of 4493 nm/RIU, the 70 nm thick InN layer based fiber optic SPR sensor illustrates good sensing behavior.     

Theoretical and experimental studies on coupler based fiber optic displacement sensor with concave mirror

A new fiber optic displacement sensor (FODS) is proposed and demonstrated using a multimode fiber coupler as a sensor probe and a concave mirror as a reflective target. A mathematical model is also developed to investigate the performance of proposed FODS at various coupling ratio, fiber diameter, and surrounding media. Three slopes are obtained for the displacement response where the third slope starts at a displacement position of twice the focal length. The numerical results show that higher performance is attained at lower coupler ratio of 50:50 or smaller core diameter. The results also show that the proposed FODS has a potential application in liquid and gas chemical sensors. The experimental performances are also investigated for the proposed sensor where it is observed that the second peak of the displacement curve is located at exactly two times of the focal length or 20 mm.     

光源谱宽对法布里-珀罗干涉式光纤传感器工作灵敏度的影响

对干涉式光纤传感器来说,光源的谱宽直接影响着传感器的工作特性。从法布里—珀罗干涉式光纤传感器出发,推导其灵敏度的理论表达式,并用MathCAD软件进行了数学分析。讨论了光源谱宽对传感器灵敏度的影响。介绍了具有温度反馈功能的法布里—珀罗光纤干涉实验系统,给出了用该实验系统拍摄的谐振曲线照片。从该系统进行的两个重要的实验(不同干涉腔长的灵敏度对比实验和不同干涉长度的光源实验)表明,法布里—珀罗干涉式光纤传感器的灵敏度与光源谱宽的理论表达式是正确的,理沦公式与实验结论能很好地吻合。最后指出了该方法可以用于分析其他类型的干涉式光纤传感器的灵敏度问题,为光源的选择提供了参考。     

Micro double tapered optical fiber sensors based on the evanescent field-effect and surface modification

A double tapered optical fiber sensor based on evanescent field-effect and surface modification technology was introduced in this work. Whether the liquid and gas molecules had polarities or not, they all could be detected by the sensors modified in different silane coupling agents. At the same time, the sensing characters of the single mode optical fiber with three different tapering lengths were researched, and it came to a conclusion that the optical fiber sensor had stronger evanescent field effect and higher sensitivity when length of tapered fiber was 30 mm. The functionalized tapered fibers modified by 3-aminopropyltrimethoxy silane (APTES) or 3-methylpropenylacyloxy propyltrimethoxy silane (MPAPTES), were employed to detect the polar or nonpolar molecules which had corresponding features. Further, the results of quantitative tests showed that the fiber optic sensor was sensitive to the change of the ethanol concentration and the characteristic peaks of the absorption power spectra could reach to 3–5 dB.     

LED based fiber optic surface plasmon resonance sensor

Modeling of a miniaturized fiber optic sensor based on surface plasmon resonance utilizing a broad band diffuse source is presented. Attenuated total internal reflection with Kretschmann configuration is the basis of the theoretical model. For simulation both meridional and skew rays are considered. The performance of the sensor is evaluated in terms of sensitivity, detection accuracy and signal to noise ratio. Effects of the numerical aperture of the fiber, core diameter and length of the sensing region on the performance parameters of the sensor are studied. The results are obtained for gold and silver metallic layer on the core of the fiber. The theoretical results obtained are compared with SPR based fiber optic sensor utilizing focused beam on the end face of the fiber from a collimated source. The advantages of using broadband LED (diffuse source) source for launching light in the fiber are the miniaturization, compactness and low cost of the sensor.     

Surface-bonded fiber optic Sagnac sensors for ultrasound detection

This paper describes a fiber optic sensor suitable for remote sensing and multi-point detection of ultrasound. This ultrasound sensor is based on the surface-bonded fiber optic Sagnac interferometer with the output fringe visibility of 1; it consists of a laser source, an ordinary single mode fiber delay line, a fiber coupler, a phase modulator and polarization controllers. For the validation of the sensor, surface acoustic waves and Lamb waves are excited by illuminating a steel specimen with an array of Q-switched Nd:YAG laser-generated line sources and the measurement of laser-generated ultrasonic waves are performed on the specimen surface using the surface-mounting fiber optic Sagnac sensor. The surface-bonded fiber optic sensor developed in this study has a simple configuration for detection of ultrasonic waves. Effectiveness of surface-bonded fiber optic Sagnac sensors for remote sensing of ultrasound and in situ monitoring of structures is investigated. The capability of multi-point detection of ultrasound by this Sagnac sensor is also discussed.