Multiplexed Long-Base Flexible Optical Fiber Extensometers and Temperature Bragg Sensors Interrogated by Low-Coherence Interferometry

We present a novel concept of quasi-distributed flexible optical fiber extensometers fully compensated from thermal variations. Developed for structural health monitoring applications, the sensors are composed of a combination of intrinsic Fabry-Perot cavities as long-base extensometers, and point-like Bragg gratings inserted along the same fiber used as temperature sensors. This configuration enables a high degree of multiplexing, thus quasi-distributed sensing, and very efficient temperature compensation. Both types of sensors are read by a fiber-optic low-coherence interferometer, used in an original way to measure simultaneously the length variations of the cavities and the wavelength shifts of the Bragg gratings. Finally, we present the experimental validation of the whole measurement system, suitable for concrete structures instrumentation, as it includes an original optical fiber sheath packaging the optical fiber as a flexible sensor.     

影响光纤温度传感器应用的两个主要因素

从光纤温度传感器出生,并在我们长期实验的基础上,分析了大多数光纤传感器难以走向实用化的原因,并提出了一定的处理方法和建议。我们认为,光纤传感器在推广应用上受到制约的重要原因是其长期稳定性和可靠性存在着问题,影响稳定性和可靠性的两个主要因素是光源输出光功率的漂移和光纤保护层的老化,尤其是位于待测区域的探头、敏感光纤和接续光纤的保护层老化问题限制了光纤传感器的应用。     

光纤燃油液位传感器研究现状

液位测量传感器是飞机燃油测量系统中的重要组成部分。光纤燃油液位传感器因其本质安全的特性而在飞机燃油液位测量领域备受关注。根据被测对象对光的调制形式不同,将光纤液位传感器分为光强调制型和波长调制型两类,总结各种传感器的原理和应用现状,讨论不同类型传感器的性能和优缺点,并对今后的发展方向做出展望。     

Chemical Detection in Water by Single-Walled Carbon Nanotubes-Based Optical Fiber Sensors

In this letter, the possibility to use single-walled carbon nanotubes (SWCNTs) as sensitive nanostructured material for the development of an optoelectronic sensor that can perform chemical detection in water has been investigated and demonstrated for the first time. The fabricated sensor has been employed in a reflectometric system involving single wavelength reflectance measurements. The good stability of the steady-state signal, the high sensitivity, as well as the good response dynamics obtained in the case of toluene detection confirm the potentiality of SWCNTs to be employed in a water environment.     

Stress Concentrations Caused by Embedded Optical Fiber Sensors in Composite Laminates

The fiber optic sensor (FOS) embedded perpendicular to reinforcing fibers causes an `Eye' shaped defect. The length is about 16 times fiber optic radius (R_Fos) and height is about 2R_Fos. The eye contains fiber optics in the center surrounded by an elongated resin pocket. Embedding FOS causes geometric distortion of the reinforcing fiber over a height equal to 6 to 8 R_Fos. This defect causes severe stress concentration at the root of the resin pocket, the interface (in the composite) between the optical fiber and the composite, and at 90° to load direction in the composite. The stress concentration was calculated by finite element modeling of a representative micrograph. The FE results agreed reasonably with analytical and experimental data in the literature for a similar problem. The stress concentration in axial direction was about 1.44 and in transverse direction at the interface was -0.165 and at resin pocket was 0.171. Under tensile loading, the initial failure was by transverse matrix cracking (fiber splitting) at the root of the resin pocket, then that lead to final fracture by fiber breakage. Under compression loading, the failure initiation was by interfacial cracking due to large transverse tensile stress and the final fracture was by compression. Fracture stress calculated from the analysis using the maximum stress criteria agreed reasonably with test data.     

Acousto-Ultrasonic Optical Fiber Sensors: Overview and State-of-the-Art

This paper gives a review of acoustic and ultrasonic optical fiber sensors (OFSs). The review covers optical fiber sensing methods for detecting dynamic strain signals, including general sound and acoustic signals, high-frequency signals, i.e., ultrasonic/ultrasound, and other signals such as acoustic emissions, and impact induced dynamic strain. Several optical fiber sensing methods are included, in an attempted to summarize the majority of optical fiber sensing methods used to date. The OFS include single fiber sensors and optical fiber devices, fiber-optic interferometers, and fiber Bragg gratings (FBGs). The single fiber and fiber device sensors include optical fiber couplers, microbend sensors, refraction-based sensors, and other extrinsic intensity sensors. The optical fiber interferometers include Michelson, Mach-Zehnder, Fabry-Perot, Sagnac interferometers, as well as polarization and model interference. The specific applications addressed in this review include optical fiber hydrophones, biomedical sensors, and sensors for nondestructive evaluation and structural health monitoring. Future directions are outlined and proposed for acousto-ultrasonic OFS.     

Mathematical Modeling of Intensity-Modulated Bent-Tip Optical Fiber Displacement Sensors

Intensity-modulated optical fiber displacement sensors have a potential to be used in a number of applications, including those in industry, military, aerospace, and medicine. Compared with other types of optical fiber sensors, intensity-modulated sensors offer distinctive advantages in that they are usually less complex, inexpensive, and less sensitive to thermal-induced strain. They are able to perform accurate contactless sensing while being of a small size and having a wide dynamic range. A common form of the intensity-modulated optical fiber sensor performs its measurement by making use of a pair of straight parallel optical fibers integrated with a moving reflector modulating the reflected optical signal intensity. Although such an optical modulation configuration exhibits good sensing ability, improvement on its performance could still be made to widen the extent of its application areas. This leads to the development of more effective intensity modulation mechanisms utilizing bent-tip optical fibers and a reflector that can either laterally slide or longitudinally move with reference to the central axis of the fibers. This paper describes such alternative sensing structures and demonstrates the derivations of mathematical models proposed for analyzing their sensing characteristics. Based on experimental studies, the models are verified and validated for the analysis of sensitivity and linearity.      

Preparation and Characterization of LaxC60 Thin Films Fabricated by Layer-by-Layer Deposition

A modification of physical properties of solid-state C₆₀ when La was doped to C₆₀ thin film as a trivalent metal was examined. the thin film was fabricated by using Layer-by-Layer deposition technique with the multi-sources evaporation system. We found that the C₆₀ film changes its electrical character from the insulator to the semiconductor rapidly upon La doping. the temperature dependence of the electrical conductivity is semiconductive with the activation energy of about 0.3eV.     

Optical Intensity-Based Measurement of Multipoint Hetero-Core Fiber Sensors by the Method of Time-Differentiation in Optical Loss

In this paper, we propose the multipoint optical intensity-based measurement of tandem connected intrinsic fiber-optic sensors by means of monitoring time-differentiation in optical loss. The use of hetero-core sensors can make it possible that a simple optical intensity-based measurement combined with a time-differentiation method could be facilitated for the multipoint measurement because the hetero-core technique has a low insertion loss and a sizable loss change in the tandem usage. Addressing multi-sensors has been successfully demonstrated including one displacement sensor and two contact sensors, which are located along a single transmission line in real-time basis. The gait system is also efficiently improved to monitor the knee flexure and the sole contact sensors located in a single transmission line with a mirror at the terminal end of fiber in order to simplify the measurement system for unconstrained monitoring.     

Frequency Modulated Continuous Wave System for Optical Fiber Intensity Sensors With Optical Amplification

We report on the use of erbium doped fiber (EDF) amplification to enhance a frequency modulated continuous wave (FMCW) technique for referencing optical intensity sensors located between two Bragg grating structures. The experiment combines the concept of FMCW with the spectrally selective mirror properties of Bragg gratings to interrogate with referencing properties intensity based sensors. The interrogation system without amplification yields a sensor resolution of around 0.078 dB. When the EDF amplifier is introduced into the experimental set up, the sensor sensitivity does not change, but the signal-to-noise ratio is improved, resulting into an enhanced resolution of 0.025 dB. We also obtain a remote sensing operation at a location of 50 km, showing the feasibility of this configuration to be used as a remote sensing application.     

多模光纤温度传感器系统

研制了钴盐溶液热色传感介质光学双波长差分吸收多模光纤温度传感器系统。自制了光纤耦合器件,采用了锁相电路,利用微机直接进行数字锁相探测,信号相除运算和温度校正。该系统实时显示温度,测温范围30℃—50℃,准确度±0.15℃,分辨率0.02℃,在40℃时6小时稳定性±0.05℃,12小时稳定性±0.18℃。主要用于抗电磁干扰的微波辐射治疗和谷物加热干燥等测温应用。     

Preparation and Characterization of La x C60 Thin Films Fabricated by Layer-by-Layer Deposition

The main product in the Krätschmer synthesis of fullerenes is a insoluble amorphous solid called fullerene black. Structural and chemical characterisation allow to conclude that this material contains irregular stacks of bent and planar carbon sheets in large variations of size and bending radius. The chemical reactivity is heterogeneous comprising elements of carbon black chemistry and of fullerene chemistry.     

Optical Fiber Sensors to Measure Collector Performance in the Pantograph-Catenary Interaction

Optical fiber sensors are proposed to detect static and dynamic collector strain for high-speed railway pantograph achieving electromagnetic immunity, nonelectrically conducting and small size. The implemented scheme based on a Michelson's interferometer with a 3 $,times,$3 coupler allows local strain measurement insensitive to temperature variations with high reliability guaranteed by the employment of standard 1550 nm optical communications components. By a test rig to experimentally simulate the pantograph-catenary contact-force the sensor performance is compared with typical electric measurement.      

分布式光纤光子传感器与测量网络的进展

本文介绍了分布式光纤光子传感器与测量网络 (DOFPSMN)的发展历史 ,系统的工作原理、系统的结构 ,硬件和软件的组成 ,国内外分布式光纤光子传感器与测量网络的研究现状和技术水平 ,应用前景和发展方向     

光纤化学传感器的研究及其在环境分析中的应用

本文综述了光纤化学传感器的特点、工作原理、类型及各类光纤化学传感器(气敏、pH、金属离子和有机化合物等)的研究进展及其在环境分析中的应用,分析了近年来光纤化学传感器的技术发展和应用趋势。     

High Speed Quantum Key Distribution Over Optical Fiber Network System

The National Institute of Standards and Technology (NIST) has developed a number of complete fiber-based high-speed quantum key distribution (QKD) systems that includes an 850 nm QKD system for a local area network (LAN), a 1310 nm QKD system for a metropolitan area network (MAN), and a 3-node quantum network controlled by a network manager. This paper discusses the key techniques used to implement these systems, which include polarization recovery, noise reduction, frequency up-conversion detection based on a periodically polled lithium nitrate (PPLN) waveguide, custom high-speed data handling boards and quantum network management. Using our quantum network, a QKD secured video surveillance application has been demonstrated. Our intention is to show the feasibility and sophistication of QKD systems based on current technology.     

Carbon Dots-Based Ultrastretchable and Conductive Hydrogels for High-Performance Tactile Sensors and Self-Powered Electronic Skin

Smart tactile sensing materials have excellent development prospects, including wearable health-monitoring equipment and energy collection. Hydrogels have received extensive attention in tactile sensing owing to their transparency and high elasticity. In this study, highly crosslinked hydrogels are fabricated by chemically crosslinking polyacrylamide with lithium magnesium silicate and decorated with carbon quantum dots. Magnesium lithium silicate provides abundant covalent bonds and improves the mechanical properties of the hydrogels. The luminescent properties endowed by the carbon dots further broaden the application of hydrogels for realizing flexible electronics. The hydrogel-based strain sensor exhibits excellent sensitivity (gauge factor 2.6), a broad strain response range (0–2000%), good cyclicity, and durability (1250). Strain sensors can be used to detect human motions. More importantly, the hydrogel can also be used as a flexible self-supporting triboelectric electrode for effectively detecting pressure in the range of 1–25 N and delivering a short-circuit current (I_SC) of 2.6 µA, open-circuit voltage (V_OC) of 115 V, and short-circuit transfer charge (Q_SC) of 29 nC. The results reveal new possibilities for human–computer interactions and electronic robot skins.