保偏微结构光纤光栅 F-P腔折射率传感特性分析

针对提高光纤光栅折射率传感器抗干扰能力以及增加反射率的需求,本文提出了一种基于Fabry-Perot腔的保偏微结构光纤(PM-MOF)布拉格光栅折射率传感器.根据传榆矩阵法和有限元方法,分析了微结构光纤光栅F-P腔中被测物折射率与F-P腔反射谱中两个偏振模谐振波长差的关系,在此基础上讨论了中心孔直径、F-P腔长度等参数对传输特性的影响.研究结果表明,随着空气孔中填充物折射率的增加,保偏微结构光纤光栅F-P腔的两个偏振态的谐振波长差将逐渐减小;F-P腔的干涉作用使反射率较单个光栅有很大提高,便于长距离传输和实时解调;两个偏振模对外界干扰具有相似的响应,因此该传感器具有更强的抗干扰能力.本文研究结果为保偏微结构光纤光栅在折射率传感器及其生物传感器方面的应用提供了理论依据.     

金属涂层SPR的单端面LPFG折射率传感器(英文)

提出了一种新型的单端面反射的镀有金属膜的长周期光纤光栅传感器.这种基于表面等离子体谐振的具有三层结构的传感器分为两个部分,光栅部分用连续CO2激光脉冲制作,金属膜是由真空镀膜制成.在光栅上镀上各种不同厚度的薄金属膜来激发表面等离子体波,用这种光纤光栅传感器来测量液体的折射率,并研究它的反射谐振谱的特性.在标准气压下,镀有80 nm银膜的光栅从水(ns=1.33)到酒精(ns=1.36)中光栅谐振波长改变了1.14nm,其敏感度达到折射率变化～5×10-4谐振波长改变20 pm.研究发现不同厚度的不同金属膜显示了不同的敏感度.通过比较光栅在空气,水,酒精,甘油,以及在它们的混合物溶液中的谐振波长,得到这种反射式的长周期光纤光栅传感器的敏感特性.为制作一种高性能的用来测量折射率的光纤光栅传感器提供了一个有益的参考.     

基于级联光栅温度补偿的溶液浓度测量研究

为解决长周期光纤光栅(LPG)折射率测量时的温度交叉敏感问题,利用布喇格光纤光栅(FBG)对环境折射率不敏感的特点,将其与长周期光纤光栅(LPG)级联,构成具有温度补偿的折射率传感方案。实验结果表明：随着温度的变化级联光栅的两个透射谐振波长都有线性变化,而改变溶液折射率时只有一个透射谐振波长改变。因此,可以利用级联光栅对折射率和温度双参量进行同时测量,补偿因温度变化产生的测量误差。     

长周期光纤光栅对掺葵花籽油的橄榄油纯度测定研究

针对当前橄榄油掺假问题,提出一种测定橄榄油纯度的新方法.将纯橄榄油和纯葵花籽油按不同比例配置得到不同纯度的待测橄榄油,用阿贝折射计测出各样品的折射率,得到样品纯度与折射率之间的线性关系.利用长周期光纤光栅传感器对外界折射率的敏感性特性,将不同纯度的待测橄榄油分别滴加到长周期光纤光栅表面;宽带光源发出的光经过其表面进入光谱仪后得到不同纯度样品的透射谱.实验测得不同纯度的橄榄油样品与衰减峰的强度变化存在线性关系,灵敏度为0.007 04dB/%,线性度较好,决定系数R2约为0.96.根据光谱仪的强度分辨率可以计算得到橄榄油纯度的探测极限为1.42%.研究结果表明,利用该长周期光纤光栅传感器可以简单、快捷、准确地测定橄榄油的纯度,具有一定的应用价值和前景.     

基于Fano共振的等离子体共振传感器

基于表面等离子体共振的金属纳米结构传感器具有测量精度高、易集成的特点,已广泛应用于生物、化学、材料、光子学和生命科学等诸多领域。然而由于表面等离子体共振在可见光波段具有较大的辐射损耗,导致等离子体共振传感器谐振峰较宽,极大地限制了传感器的性能。本文采用不对称双椭圆柱结构在等离子体共振传感器中引入不对称性,产生Fano共振以实现窄带光谱特性。通过优化结构参数,在681 nm波长处,得到了半高全宽(FWHM)仅为10.8 nm的谐振谷。该传感器在环境折射率1.0~1.1的变化范围内,折射率灵敏度可以达到299 nm/RIU,品质因数可以达到27.8。该传感器在高折射率灵敏度传感应用方面有着巨大的潜力。     

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....     

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。     

SMS光纤结构特性的数值模拟分析

采用光束传播法(BPM),对单模-多模-单模(SMS)光纤结构内部传输光场分布情况,进行数值模拟;分析了SMS光纤结构中不同的多模光纤长度,多模光纤纤芯直径和输入光波长对光纤结构内部传输光场分布情况的影响,以及所得透射谱的变化规律;进一步探讨了基于多模干涉理论的SMS光纤结构传感器在各传感领域的应用潜力.最后,以基于多模干涉理论的SMS光纤结构折射率传感器为例,分析了多模光纤纤芯外界折射率的改变对光纤结构输出透射谱的影响,并进行实验加以验证.实验结果与仿真模拟结论一致,从而验证了模拟的准确性.     

基于折射率变化的固化在线监测研究

先进复合材料的固化成型工艺十分复杂,目前在很大程度上仍依赖于经验工艺。为了实现复合材料固化工艺的透明化、科学化及智能化,提出了将光纤折射率传感器用于复合材料制造过程,研制了一种折射率光纤传感器,同时将光源、探测器、信号处理器等元器件集成化为一个便携式的光纤传感仪以利于生产现场使用。利用该传感器对常温固化树脂的固化过程进行了测量,将其与同等条件下迈克尔逊干涉仪对固化过程的监测结果进行了比较,二者具有良好的一致性。在实验室与生产现场两种条件下将光纤折射率传感器埋设于预浸料中对其固化工艺过程进行了监测。结果表明,该技术不仅可以用于新型树脂固化工艺制度的确定,也可用于复合材料固化工艺过程的在线监测。     

高精度数字折光仪

本文介绍一种新型测量液体折射率的仪器.该仪器利用光的折射原理设计,采用半导体激光器做光源,光电位置传感器做接收器,计算机控制,带有测温系统,可进行温度修正,自动显示测量结果,扩展测量不确定度为0.0001,k=2.该仪器测量蔗糖溶液时,可以显示折射率、浓度、糖度、温度等.     

Highly Sensitive Optical Refractometer Based on Edge-Written Ultra-Long-Period Fiber Grating Formed by Periodic Grooves

An ultra-long-period fiber grating with periodic groove structure (G-ULPFG) fabricated by using an edge-written method with high-frequency CO$_{2}$ laser pulses is proposed in this paper. The experimental results show that the different resonant peaks of the G-ULPFG have different temperature and refractive index sensitivities and, in particular, the refractive index sensitivity is much larger than that of conventional ULPFG due to the edge-groove structure. Such a kind of G-ULPFGs could be used as a highly sensitive optical refractometer with temperature self-compensation.      

基于准连续域束缚态介质超表面的光微流折射率传感研究

准连续域束缚态(Quasi-BIC)是超表面中一种特殊共振模,具有极高的品质因子,可以极大地提高光与物质的相互作用,在荧光增强、纳米激光、光传感以及非线性光学等领域均有重要应用。本文基于我们前期对quasi-BIC产生的理论,研究quasi-BIC介质超表面在折射率传感方面的应用。本文给出了传感系统的基本结构,利用电子束光刻技术结合注塑工艺完成了样品光流控结构的制备,并初步测试性能。研究结果表明,得益于产生quasi-BIC的新方法,该超表面具有两个高Q值quasi-BIC共振峰(1.523 µm和1.570 µm,品质因子分别为3069和4071)。以四种折射率溶液(n分别为1.450/1.462/1.470/1.480)为样品的测试实验表明,两个共振峰均能完成折射率检测,灵敏度S分别为452 nm/RIU、428 nm/RIU,性能评价指标FOM分别为376.7、372,优于现有文献;共振波长和折射率之间线性度良好,展现了quasi-BIC超表面在折射率传感中的应用潜力。

     

Origin of the positional offset of FP-like enhanced transmission peaks in a one-dimensional gold grating

General transmission characteristics of a one-dimensional optically thick gold grating were investigated as functions of the grating structural parameters (period, slit width and grating thickness) in the spectral range from 0.4 μm to 9.9 μm. The positions (resonant wavelengths) of the Fabry–Perot (FP)-like enhanced transmission (ET) peaks depend not only on the grating’s period and thickness, but also on the slit width. These numerically calculated FP-like resonant positions are different from the simple FP predictions. The physical origin of these positional offsets is ascribed to the additional phases produced by the special ‘reflecting planes’, which are caused by oscillating dipoles located at the entrances and exits of the slits. For a particular order of FP-like resonance, the additional phase is found to be independent of the refractive index of the surrounding, but dependent on the grating’s structural parameters.     

啁啾光子晶体光纤光栅反射谱和时延特性研究

用有限元法和传输矩阵法,对基于包层空气孔为柚子型结构的光子晶体光纤啁啾光栅的反射谱进行了理论分析。通过对均匀光栅仿真结果与实验结果的对比,可知此方法是可行的。研究表明光子晶体光纤的啁啾光栅有多个明显的反射峰,并且分析了啁啾系数、折变量对各谐振峰带宽和反射率等的影响。计算结果显示,随着啁啾系数和折变量的增大,光栅反射谱呈规律变化,当啁啾系数增大到一定程度时几个反射峰会连到一起,形成一个大的反射带宽。同时对光栅基模反射谱对应的时延特性进行了研究,可知其同样具有比较平滑的时延曲线,可以用于色散补偿。     

Versatile waveguide-coupled optofluidic devices based on liquid core optical ring resonators

A versatile waveguide-coupled optofluidic device using the liquid core optical ring resonator (LCORR) that can be operated with liquid of any refractive index (RI) is theoretically analyzed and experimentally demonstrated. The results confirm the confinement of resonant modes for all sample RIs, and reveal that confined modes in a high-RI core are excited by an external waveguide by resonant tunneling through the LCORR wall. It is further found that a thin wall must be used for effective interaction between the core mode and the waveguide. The results have important applications in optofluidic devices, including sensors, microfluidic lasers, and nonlinear optics.     

Composite‐Scattering Plasmonic Nanoprobes for Label‐Free,Quantitative Biomolecular Sensing

Biosensing based on localized surface plasmon resonance (LSPR) relies on concentrating light to a nanometeric spot and leads to a highly enhanced electromagnetic field near the metal nanostructure. Here, a design of plasmonic nanostructures based on rationally structured metal–dielectric combinations is presented, called composite scattering probes (CSPs), to generate an integrated multimodal biosensing platform featuring LSPR and surface‐enhanced Raman spectroscopy (SERS). Specifically, CSP configurations are proposed, which have several prominent resonance peaks enabling higher tunability and sensitivity for self‐referenced multiplexed analyte sensing. Using electron‐beam evaporation and thermal dewetting, large‐area, uniform, and tunable CSPs are fabricated, which are suitable for label‐free LSPR and SERS measurements. The CSP prototypes are used to demonstrate refractive index sensing and molecular analysis using albumin as a model analyte. By using partial least squares on recorded absorption profiles, differentiation of subtle changes in refractive index (as low as 0.001) in the CSP milieu is demonstrated. Additionally, CSPs facilitate complementary untargeted plasmon‐enhanced Raman measurements from the sample's compositional contributors. With further refinement, it is envisioned that the method may lead to a sensitive, versatile, and tunable platform for quantitative concentration determination and molecular fingerprinting, particularly where limited a priori information of the sample is available.     

High sensitivity of taper-based Mach-Zehnder interferometer embedded in a thinned optical fiber for refractive index sensing

A taper-based Mach-Zehnder interferometer (MZI) embedded in a thinned optical fiber is demonstrated as a highly sensitive refractive index (RI) sensor. A RI sensitivity of 2210.84 nm/RIU (refractive index unit) is obtained at the external RI of 1.40, which is ten times higher than that of normal taper- and long-period fiber grating (LPFG)-based sensors. The sensitivity can be further improved by decreasing the diameter of the thinned fiber and increasing the interferometer length of the MZI. The proposed MZIs have lower temperature sensitivities compared with normal fiber sensors, which is a desirable merit for RI sensors to reduce the cross sensitivity caused by thermal drift.     

Optimisation of distributed feedback laser biosensors

A new integrated optical sensor chip is proposed, based on a modified distributed- feedback (DFB) semiconductor laser. The semiconductor layers of different refractive indices that comprise a laser form the basis of a waveguide sensor, where changes in the refractive index of material at the surface are sensed via changes in the evanescent field of the lasing mode. In DFB lasers, laser oscillation occurs at the Bragg wavelength. Since this is sensitive to the effective refractive index of the optical mode, the emission wavelength is sensitive to the index of a sample on the waveguide surface. Hence, lasers are modelled as planar waveguides and the effective index of the fundamental transverse electric mode is calculated as a function of index and thickness of a thin surface layer using the beam propagation method. We find that an optimised structure has a thin upper cladding layer of ~0.15 mum, which according to this model gives detection limits on test layer index and thickness resolution of 0.1 and 1.57 nm, respectively, a figure which may be further improved using two lasers in an interferometer-type configuration.     

Enhancing the tuning range of a single resonant band long period grating while maintaining the resonant peak depth by using an optimized high index indium tin oxide overlay

We report laboratory test results of a long period grating (LPG) that can maintain a constant resonant peak depth over an enhanced tuning range when it is coated with an indium tin oxide (ITO) electrode that has optimized thickness and refractive index. The authors have experimentally demonstrated a LPG coated with ITO that can be tuned in excess of 200 nm with an ambient refractive index change of less than 0.01. To the best of the authors' knowledge, this is the highest sensitivity reported for a LPG to date. In addition to the tuning performance, the resonant peak remains within 1 dB of its maximum depth for at least 100 nm of the tuning range.     

ITO Coated Optical Fiber Refractometers Based on Resonances in the Infrared Region

In this work, it is presented the fabrication of optical fiber refractometers in the infrared region based on the deposition of indium tin oxide (ITO) coatings onto optical fibers core. ITO coatings act as the resonance supporting layer allowing the coupling of light at specific wavelengths from the waveguide to the ITO-coating/external medium region as a function of the refractive index of the external medium. The utilization of ITO coatings allows the fabrication of robust, highly reproducible and easy to implement resonance based refractometers. The results obtained showed an average sensitivity of 3125 nm/refractive index unit, which is comparable to the existing devices based either on resonance or other techniques. The fabricated devices showed fast response and no dependence with the length of the sensitive region.