基于温敏液体封装的高灵敏光纤多模干涉温度传感器

提出并研究了一种基于光纤多模干涉理论的温度传感器,其传感结构由毛细钢管封装一段单模-多模-单模（SMS）结构,并在管内填充温敏液体而制成.鉴于光纤多模干涉光谱对折射率具有红移特性,选择合适折射率的温敏液体进行封装可实现此结构的温度增敏.实验结果表明,在10 ～90℃的温度范围内传感器具有最大的灵敏度为-3.15nm/℃,较未封装之前提高了300多倍.     

包层腐蚀光纤M-Z干涉型高灵敏度折射率传感器(英文)

我们设计并制作了一种基于Mach-Zehnder干涉的高灵敏折射率传感器,其结构由两个光纤纤芯偏移的熔接结经包层腐蚀后组成。首先,利用商用的光纤熔接机在单模光纤上制作两个光纤纤芯偏移的熔接结;然后,将光纤化学腐蚀获得细薄的光纤包层,则光纤倏逝场与周围介质强烈相互作用,即制作出Mach-Zehnder干涉型高灵敏折射率传感器。实验结果表明,制作的长度为10 mm、直径为13.2μm的Mach-Zehnder干涉型折射率传感器,在折射率1.333～1.3685和1.3685～1.386范围内,其传感灵敏度分别高达1288.05和2118.26 nm/RIU。该传感器具有高灵敏度、结构紧凑、制作简单和低成本的优势。     

光纤布线兵法之热点问题

1什么是单模与多模光纤？他们的区别是什么？单模与多模的概念是按传播模式将光纤分类—多模光纤与单模光纤传播模式概念。我们知道,光是一种频率极高（3×1014Hz）的电磁波,当它在光纤中传播时,根据波动光学、电磁场以及麦克斯韦式方程组求解等理论发现：当光纤纤芯的几何尺寸远大于光波波长时,     

高斯光束到光纤的单透镜耦合

分析了基模高斯激光束到单模和多模光纤的单透镜耦合过程中的各种损耗,把多模光纤的光场用高斯分布近似,采用模场耦合理论计算了基模高斯光束到单模和多模光纤的单透镜耦合效率.模拟计算了当激光-光纤耦合系统的工程参数(光束束宽、光纤数值孔径和光纤的纤芯芯径)一定时,单透镜耦合效率与所选用透镜的焦距之间的关系.并利用532mn激光(M2≤1.05)在几种不同焦距的透镜下对纤芯直径为3.μm的单模光纤和25μm的多模光纤进行了耦合效率的测定实验,得到了与理论计算基本吻合的实验结果.     

基于氧化石墨烯的干涉型光纤湿度传感器

氧化石墨烯是一种新型二维纳米碳材料,比表面积较大,亲水性突出,折射率随湿度变化显著,可用于高灵敏度的光纤湿度传感.我们提出并实验验证了一种基于氧化石墨烯的干涉型光纤湿度传感器,在保偏光纤与普通单模光纤的两个熔接点处分别采用花生形光纤结构与错位熔接,构建在线型光纤Mach-Zehnder干涉仪,并通过沉积将氧化石墨烯均匀地镀在保偏光纤表面.当环境湿度变化时,氧化石墨烯薄膜吸附或释出水分子,其折射率发生变化,改变包层模的有效折射率,进而导致干涉条纹的强度变化.实验结果表明,在35%~65%RH的测量范围内该传感器具有灵敏度高达0.165dB/%RH的线性响应,因此具有灵敏度高,结构简单的优点.     

基于双模LPFG折射率不敏感双参量传感器

环境折射率和环境温度变化是影响光纤应变测量误差的主要因素。本文利用双模光纤纤芯双模式(LP01和LP11)支持特性设计了一款环境折射率不敏感的双模光纤(DMF)长周期光纤光栅(LPFG)应变传感器。设计了传感器模型结构,制作了最优化参数的传感器样品。实验测试了DMF-LPFG传感结构对外部环境中应变、温度和折射率的响应。通过在单模光纤上用紫外激光刻写的布拉格光栅(FBG)解决了环境温度的交叉影响。轴向应变实验结果表明,该新型结构传感器在0με~840με应变范围内其轴向应变灵敏度可以达到-5.4 pm/με,该灵敏度值相比较于普通LPFG有很大提高。温度在25℃~80℃范围内其灵敏度为58.86 pm/℃,表现出较好的线性度。同时,传感器对环境折射率变化表现出不敏感特性。通过采用双参数矩阵对少模LPFG和FBG的应变和温度灵敏度进行处理,可以实现双参数的同时解调。该新型复合光栅结构具有良好的传感性能和工程应用前景。     

光纤出射光强分布研究

对多模光纤出射光束的光强分布用横向位移法进行了理论分析和实验研究,并用数值计算的方法分析实验测量数据.结果表明,高斯光束可以很好地描述光纤出射光强的分布,光纤出射光束光强分布参数主要与光纤芯径和出纤光功率等有关,为强度调制型光纤传感器的优化研制提供了必要的实验依据.     

埋入光纤进行复合材料中的应变测量

由于光纤传感器所具有的特点, 把光纤埋入复合材料内部进行应变测量, 从而监测复合材料的性能改变, 是随着智能复合材料结构的研究而发展起来的一项新技术, 本文用弱波导理论的有关结果研究了光纤在受到力作用时, 光纤应变和其中传输光的位相改变之间的关系, 计算了Corning 光纤在轴向应力作用下的应变-位相灵敏度, 为形成干涉型光纤传感器提供理论基础; 同时给出了单向受力情况下的实验验证, 分析了误差原因。      

锥脊波导SOA光耦合机制的理论分析

针对半导体光放大器（SOA）与单模光纤的耦合问题，详细介绍了当前最新的锥脊光波导耦合技术，用光波电磁场干涉理论建立了锥脊光波导的传输模式方程，并根据光波的全反射理论，揭示了锥脊光波导等效折射率的渐变规律，从理论上分析了锥脊波导SOA的光耦合机制，理论分析与相关报道的实验结果吻合。     

掺杂分布对多模光纤放大器输出特性的影响

针对高功率多模光纤放大器中稀土离子掺杂分布和形状对系统输出特性的影响,本文进行了数学模拟和理论分析.根据多模掺杂光纤速率方程考虑了种子光端面激励特性,并对纤芯模式耦合系数矩阵进行了修正,建立了多模光纤放大器理论模型.通过对功率传输方程组的求解,数值模拟了不同激励条件下6种均匀和抛物线形掺杂的双包层掺Yb3+光纤接入放大器的输出特性.计算结果证明:不同激励条件下,掺杂离子分布对输出特性的影响存在差异;通过设计光纤内掺杂离子分布规律和形状能有效抑制放大器中的高阶模式,提高输出光的光束质量.     

Integration of micrometer-sized polymer elements at the end of optical fibers by free-radical photopolymerization

A simple method of manufacturing micrometer-sized polymer elements at the extremity of both single-mode and multimode optical fibers is reported. The procedure consists of depositing a drop of a liquid photopolymerizable formulation on a cleaved fiber and using the light that emerges from the fiber to induce the polymerization process. After exposure and rinsing a polymer tip is firmly attached to the fiber as an extension of the fiber core. It is shown that the tip geometry can be adjusted by the variation of basic parameters such as the geometry of the deposited drop and the conditions of drop illumination. When this process is applied to a multimode fiber three-dimensional molds of the fiber's linearly polarized modes can be obtained. The process of polymer-tip formation was simulated by a numerical calculation that consisted of an iterative beam-propagation method in a medium whose refractive index is time varying. It is shown that this process is based on the gradual growth, just above the fiber core, of an optical waveguide in the liquid formulation. Experimental data concerning two potential uses of the tipped fibers are presented.     

Specklegram in a grapefruit fiber and its response to external mechanical disturbance in a single-multiple-single mode fiber structure

Specklegram in multimode fiber has successfully been used as a sensor for detecting mechanical disturbance. Speckles in a multimode pure silica grapefruit fiber are observed and compared to that of a step-index multimode fiber, showing different features between them. The sensitivities to external disturbance of two kinds of fiber were measured, based on single-multiple-single mode (SMS) fiber structure. Experimental results show that the grapefruit fiber shows higher sensitivity than does the step-index multimode fiber. The transmission spectrum of the grapefruit fiber was measured as well, showing some oscillation features that are significantly different from that of a step-index multimode fiber. The experiments may provide suggestions to understand the mechanisms of light propagation in grapefruit fibers.     

Highly sensitive detection of proteins and bacteria in aqueous solution using surface-enhanced Raman scattering and optical fibers

We report the detection of the proteins lysozyme and cytochrome c as well as the live bacterial cells of Shewanella oneidensis MR-1 in aqueous solutions with sensitivities order(s) of magnitude higher than those previously reported. Two highly sensitive surface-enhanced Raman scattering (SERS)-based biosensors using optical fibers have been employed for such label-free macromolecule detections. The first sensor is based on a tip-coated multimode fiber (TCMMF) with a double-substrate "sandwich" structure, and a detection limit of 0.2 μg/mL is achieved in protein detections. The second sensor is based on a liquid core photonic crystal fiber (LCPCF) with a better confinement of light inside the fiber core, and a detection limit of 10(6) cells/mL is achieved for the bacteria detection. Both SERS biosensors show great potential for highly sensitive and molecule-specific detection and identification of biomolecules.     

Stress optical fiber sensor using light coupling between two laterally fused multimode optical fibers

A stress optical fiber sensor was manufactured and tested. It uses light coupling between two parallel and laterally fused, all-silica multimode optical fibers along a cladding length of a few centimeters. This sensor is dedicated to the measurement of high values of stress. A theoretical model was developed using the mode coupling and the perturbation theory to calculate the global coupling coefficient of light. A serial optical fiber sensor network interrogated by the time-division multiplexing method was realized and tested. The major applications of this sensor are control and monitoring of civil engineering structures and concretes.     

Side-polished multimode fiber biosensor based on surface plasmon resonance with halogen light

A side-polished multimode fiber sensor based on surface plasmon resonance (SPR) as the transducing element with a halogen light source is proposed. The SPR fiber sensor is side polished until half the core is closed and coated with a 37 nm gold thin film by dc sputtering. The SPR curve on the optical spectrum is described by an optical spectrum analyzer and can sense a range of widths in wavelengths of SPR effects. The measurement system using the halogen light source is constructed for several real-time detections that are carried out for the measurement of the index liquid detections for the sensitivity analysis. The sensing fiber is demonstrated with a series of refractive index (RI) liquids and set for several experiments, including the stability, repeatability, and resolution calibration. The results for the halogen light source with the resolution of the measurement based on wavelength interrogation were 3 x 10(-6) refractive index units (RIUs). The SPR dip shifted in wavelength is used as a measure of the RI change at a surface, and this RI change varies directly with the number of biomolecules at the surface. The SPR dip shift in wavelength, which was hybridized at 0.1 microM of the target DNA to the probe DNA, was 8.66 nm. The all-fiber multimode SPR sensor, which has the advantages of being low cost, being disposable, having high stability and linearity, being free of labeling, and having potential for real-time detection, permit the sensor and system to be used in biochemical sensing and environmental monitoring.     

Micro-optical 1 x 4 fiber switch for multimode fibers with 600-microm core diameters

The design, manufacture, and test of a 1 x 4 micro-optical fiber switch for multimode fibers with 600-microm core diameters are described. Microlens array telescopes allow for variable and fast beam deflection when the positions of the cylindrical microlens arrays relative to each another are altered by specially designed piezomechanical actuators. Standard achromats are used for collimation of light emitted by the input multimode fiber and for focusing of the deflected light onto a linear array of output multimode fibers. Design and assembly of micro-optical as well as of optomechanical components are discussed. Insertion loss and cross talk are measured, and the results are compared with those of numerical optical simulations. Measurements of switching time and long-term stability, as well as of thermal behavior, are also presented.     

Propagation of light trapped within a set of lowest-order modes of graded-index multimode fiber undergoing bending

We describe experimental results and a theoretical analysis for propagation in graded-index multimode fiber when diode laser light is launched into the lowest-order propagation modes and the fiber undergoes severe bending perturbations. Experimentally, near-field modal interference images and transmission loss measurements were obtained for different loop diameters. The data indicate that, when the fundamental mode is excited, the light remains in lowest-order modes even for small bend diameters. This is consistent with analysis which predicts that, in a parabolic-index multimode fiber subject to constant diameter bending, the light tends to oscillate between lowest-order modes and remains trapped therein rather than diffusing to high-order modes. Implications of these results for an intrusion-resistant communication system with graded-index multimode fiber are discussed.     

Simulation, implementation, and analysis of an optical fiber bundle distance sensor with single mode illumination

A simulation model for an optical fiber bundle distance sensor with a single mode fiber as the illumination fiber and a multimode fiber as the receiving fiber is presented. Approximating the illumination light exiting the single mode fiber as having a Gaussian intensity profile, a closed-form solution of the reflected light coupled into the receiving fiber was derived. A distance sensor was implemented and the measured sensor outputs were compared with the simulation data to verify the theoretical model. The performance of the distance sensor with different design parameters was analyzed. Design guidelines for achieving desired sensor performances are suggested.