侧边抛磨的U型金溅射塑料光纤等离子体共振传感器

为了测量溶液折射率变化，对塑料光纤纤芯表面的纤芯-金层-液体的3层膜结构进行研究，制作了一种使用U型结构并结合侧边抛磨方法的表面等离子体共振传感器。将截取的一段塑料光纤弯曲成为U型，并在烘箱中通过较高温度使这段光纤的曲率固定，对弯曲部分的外表面进行抛光，暴露该位置塑料光纤芯层并在其上溅射金纳米薄膜层，将制备好的传感器浸入不同折射率的液体中，使用光谱分析仪观察光谱的移动。实验结果表明:当塑料光纤SPR传感器测量折射率变化范围在1.333~1.406的液体时，可以通过光谱观察到随着液体折射率的增大，等离子体共振吸收峰位置也不断地向波长增大的方向移动，并且二者之间存在线性关系，其灵敏度为7.5×10-4 RIU/nm。该传感器探头具有灵敏度高、小型化、易制备、低成本的特点。     

Refractive-index dispersion measurement of bulk optical materials using a fiber raman laser widely tunable in the visible and near-infrared

We propose a simple, highly sensitive fiber-optic autocollimation method for refractive-index dispersion measurement of solid-state and liquid bulk optical materials using a double-pass fiber Raman laser with Littrow-prism-tuned emission. The optical fiber is a key element of the scheme and serves simultaneously as a point laser source for the test, as a highly sensitive point receiver (or spatial filter) of the autocollimation backreflectance signal and as a medium for nonlinear frequency conversion and generation of a broadband continuum spectrum. When the Raman medium is a graded-index multimode fiber with powerful pumping (over 100 kW) using the second harmonic of a Q-switched Nd:YAG laser (λ_p=532nm), we obtain widely tunable (0.54-1.01 μm) generation in both the visible and near-IR ranges. The results obtained in the refractive-index dispersion measurements are fitted to the Sellmeier dispersion equation and the standard deviation of the experimental data from the analytical curve does not exceed 5x10^-5.     

内置调制层型光纤表面等离子体波共振传感器研究

研究了一种基于内置调制层结构的光纤表面等离子体波共振(SPR)传感器。通过在金膜与纤芯的内侧增覆具有不同厚度和属性的光学透明薄膜作为内调制层,构成了性能独特的光电复合薄膜,起到调节倏逝波矢量和金膜表面等离子体振荡波矢量的双重作用,进而控制共振效应,为调节灵敏度提供依据。采用时域有限差分方法对内置调制层结构光纤SPR共振激励模型属性进行数值仿真。在此基础上,研制了用于液体折射率测量的内置调制层型光纤SPR传感探针。实验结果表明,该传感器在1.335～1.392折射率范围内,随着待测液体折射率的增大,SPR共振光谱向长波方向偏移,且灵敏度达到2263.1nm/RIU,与基于纤芯-金膜-环境介质三层结构的常规光纤SPR传感器相比提高一倍,能够更好地满足环境折射率检测的需求。     

D-type fiber biosensor based on surface-plasmon resonance technology and heterodyne interferometry

A D-type fiber biosensor based on surface-plasmon resonance (SPR) technology and heterodyne interferometry is presented. The sensing device is a single-mode optical fiber in which half the core is polished away and a thin-film layer of gold is deposited. We measure the phase-difference variations instead of the light intensity as in traditional SPR techniques. Therefore the accuracy and resolution of our method are very high. Its sensitivity can reach 2 x 10(-6) refractive-index units. The sensor has some merits, e.g., tunable high sensitivity, small size, lower cost, smaller sample volume, and suitability for in vivo testing. This novel method of a D-type fiber biosensor based on SPR technology and heterodyne interferometry is valuable for chemical, biological, and biochemical sensing, and the novel method of D-type fiber biosensing is a feasible means of study.     

基于SM-NCF反射光谱辨识的液体折射率监测方法

针对分子生物学与环境监测领域高灵敏度特异性检测需求,提出一种基于反射光谱特征辨识的单端反射式光纤折射率传感器模型,并给出了这种基于多模干涉原理的单模光纤-无芯光纤(Single mode fiber-No core fiber, SM-NCF)串接结构传感机理及其理论模型。无芯光纤实质上是一种结构特殊的多模光纤,在实际应用中无芯光纤结构本身作为纤芯,外界环境介质当作包层,构成光波导结构。这与普通多模光纤相比,不需要采用氢氟酸对多模光纤的包层进行化学腐蚀,不会降低光纤的机械性能,也不会破坏芯模传输条件,可以更好的实现对周围环境折射率的传感监测。当无芯光纤所处外界环境折射率发生改变时,其波导结构和包层有效折射率均会发生改变,从而引起传输光信号的纵向传播常数和模场分布也会随之发生改变,最终导致不同波长对应传输光功率的变化。上述效应反映在反射光谱上,即干涉波谷对应的谐振波长、波谷峰值强度以及半波宽度发生相应变化,通过辨识该反射光谱特征就可实现对外界环境折射率的测量。借助光束传播法(BPM),数值模拟得到无芯光纤长度分别为自映像距离和非自映像距离时的SM-NCF内部光场能量分布规律,并制作了无芯光纤长度分别为自映像距离和非自映像距离的SM-NCF光纤折射率传感探头,将作为传感区域的无芯光纤一端与标准单模光纤熔接,采用磁控溅射技术在无芯光纤另一端面镀上金膜,用以提升反射光谱强度。在此基础上,搭建了基于SM-NCF终端反射型的光纤折射率试验系统,并开展了相关实验研究。研究结果表明,当无芯光纤长度是15 mm(自映像距离)时,随着液体折射率从1.331 5依次增大至1.390 2,SM-NCF反射光谱逐渐向长波方向偏移,其反射峰谐振波长对应的折射率灵敏度约为197.57 nm·RIU-1,相关系数为0.93;反射峰值强度也呈现逐渐降低趋势,其折射率灵敏度约为-62.80 dB·RIU-1。当无芯光纤长度是20 mm(非自映像距离)时,随着液体折射率依次增大,SM-NCF反射光谱呈现明显双峰现象,且均逐渐向长波方向偏移,dip2谐振峰波长折射率灵敏度约为133 nm·RIU-1,相关系数为0.96;反射峰值强度也呈现逐渐降低趋势,其折射率灵敏度约为-31.66 dB·RIU-1。对比分析可知,不论是从反射峰谐振波长偏移的角度,还是从反射峰值强度的角度,自映像距离长度对应的 SM-NCF终端反射型光纤传感器均具有较高灵敏度。对于相同折射率液体环境,非自映像距离长度对应的SM-NCF反射光谱半波宽度与自映像距离长度相比,呈现显著变窄趋势。相对于SMS透射型传感结构,当传感区域长度相同时,SM-NCF反射型结构能够实现对光波信号的往返两次调节。这种终端反射型SM-NCF传感器改进了传统透射型折射率传感器不便与待测液体相接触的缺点,具有结构简单、易于制作、抗电磁干扰能力强以及便于远程遥测等优点,能够为后续生化与环保监测领域研究应用提供有益支持。     

High-sensitivity, evanescent field refractometric sensor based on a tapered, multimode fiber interference

We propose and experimentally demonstrate an enhanced evanescent field fiber refractometer based on a tapered multimode fiber sandwiched between two single-mode fibers. Experiments show that this fiber sensor offers ultrahigh sensitivity [better than 1900 nm/RIU at a refractive index (RI) of 1.44] for RI measurements within the range of 1.33-1.44, in agreement with the theoretical predictions. This is the highest value reported to date (to our knowledge) in the literature.     

反射式光纤表面等离子体波共振传感器特性研究

研究了一种基于表面等离子体波共振(SPR)光谱分析的折射率检测新方法。研究发现,表面等离子体波共振效应光谱特征的折射率灵敏度会随着液体性质变化而发生改变。根据折射率测量范围不同,分别选择共振波长和共振强度作为检测参量,实现理论折射率分辨力达到10~(-5)数量级以上。在理论分析和实验基础上,设计出一种基于共振光强检测的终端反射式光纤表面等离子体波共振效应传感系统,采用将传感信号和基准光信号的比值作为液体折射率变化的度量值。在1．3325～1．3991的折射率测量范围内,度量值与折射率之间呈现单调递减关系,线性相关系数为0．9983。通过定义耦合系数,还可实现对表面等离子体波共振效应效应强弱和变化趋势的评估。     

Multiple-beam interference fringes applied to investigate the index profile of the optical fiber dip

A numerical-based phase shift method is presented to study optical fibers having a dip in the refractive index profile at the center of the core. Mathematical expressions for the shape of multiple-beam Fizeau fringes crossing a graded-index optical fiber (GRIN) comprising a central graded-index dip or GRIN fiber with a constant refractive index dip, immersed in a silvered liquid wedge, are derived. The index profile parameters of the central dip are determined by comparing the theoretical fringe shape across the fiber cross-section and the experimental fringe shape obtained from micro-interferograms of the wedge interferometer.     

基于表面等离子体共振和定向耦合的D形光子晶体光纤折射率和温度传感器

利用光子晶体光纤结构的灵活性和性能的优越性, 设计了一种基于D形光子晶体光纤的折射率和温度传感器. 在D形光子晶体光纤表面抛磨并镀上金纳米薄膜, 作为表面等离子体共振传感通道用来测量液体折射率; 在包层的一个空气孔中填充温敏液体甲苯, 作为定向耦合通道实现对温度的测量. 进一步的数值计算发现, 基于定向耦合效应的温度传感和基于表面等离子体共振的折射率传感相互独立, D形光子晶体光纤同时进行折射率和温度传感检测. 在各向异性的完美匹配层边界条件下利用全矢量有限元法对该传感器特性进行了数值研究, 发现D形光子晶体光纤的空气孔直径决定了定向耦合吸收峰的中心波长和温度传感的灵敏度, 金薄膜的厚度和D形结构的抛磨深度仅影响表面等离子体共振峰的相对强度. 结果表明: 该传感器在-10–80 ℃的温度范围内具有11.6 nm/℃的温度灵敏度, 在1.34–1.44折射率范围内折射率灵敏度最高可达26000 nm/RIU.     

Tapered fiber optic surface plasmon resonance sensor for analyses of vapor and liquid phases

We report a new approach to analyze both vapor and liquid phases by utilizing a tapered fiber optic surface plasmon resonance (SPR) probe. This technique employs a fiber optic SPR probe with a modified geometry to tune the SPR coupling wavelength-angle pair. The observed composite spectrum included two distinct SPR dips associated with surface plasmons excited in the gas and liquid active regions. This sensor is able to detect refractive index changes in both vapor and liquid phases individually by simultaneous monitoring SPR coupling wavelengths from the two sensing surfaces.     

Evanescent field-based optical fiber sensing device for measuring the refractive index of liquids in microfluidic channels

We report a simple optical sensing device capable of measuring the refractive index of liquids propagating in microfluidic channels. The sensor is based on a single-mode optical fiber that is tapered to submicrometer dimensions and immersed in a transparent curable soft polymer. A channel for liquid analyte is created in the immediate vicinity of the taper waist. Light propagating through the tapered section of the fiber extends into the channel, making the optical loss in the system sensitive to the refractive-index difference between the polymer and the liquid. The fabrication process and testing of the prototype sensing devices are described. The sensor can operate both as a highly responsive on-off device and in the continuous measurement mode, with an estimated accuracy of refractive-index measurement of approximately 5 x 10(-4).     

Sensitivity enhancement for a multimode fiber sensor with an axisymmetric metal grating layer

This paper proposes a novel design for a surface plasmon resonance (SPR) fiber sensor with an axisymmetric sub-wavelength metal grating layer. The relationship between the sensor performance (the sensitivity S and the quality factor Q of the SPR dip) and the characteristic parameters are investigated. Numerical simulation results show that the proposed sensor can achieve a maximum sensitivity of 13,000 nm/RIU (refractive index unit) for a refractive index range from 1.3 to 1.4.     

光纤法布里-珀罗复合结构折射率传感器的灵敏度分析

理论上推导了光纤法布里-珀罗复合结构传感器的反射光谱条纹对比度与外界介质折射率的关系,并分析了实验参数对传感器灵敏度的影响.利用化学腐蚀渐变折射率多模光纤制作了光纤法布里-珀罗复合结构折射率传感器,空气中的条纹对比度可达30 dB以上,折射率测量的灵敏度达45 dB/RIU(refraction index unit,简RIU)以上.实验结果与理论符合很好.通过理论和实验分析,提出了进一步提高传感器灵敏度的方法. 关键词： 光纤传感器 法布里-珀罗复合结构 折射率测量 灵敏度     

螺旋形塑料光纤表面等离子体共振折射率传感器

研究了基于波长调制的螺旋形塑料光纤(plastic optical fiber, POF)表面等离子体共振(surface plasmon resonance, SPR)折射率传感器。采用机械热压和扭曲法将塑料光纤制备成螺旋形,在螺旋形POF上通过磁控溅射蒸镀一定厚度(约50 nm)的金属薄膜来激励SPR效应,从而形成螺旋形POF-SPR传感器。通过对螺旋形POF-SPR传感器的结构进行修饰,研究不同结构参数对折射率传感特性的影响。实验结果表明:由厚度为500μm扁平形POF扭制、螺纹数为4的螺旋形POF-SPR传感器具有较好的线性度和折射率传感特性,在折射率为1.335～1.400范围内测得的灵敏度为1 262 nm/RIU。该传感器具有成本较低、制备简单、结构稳定等优点。     

Packaging and Characteristics of a Tapered Fiber Sensor for Refractive-Index Measurements

In this study, we demonstrate the design and fabrication of a tapered fiber sensor with a sensing application based on a new (high-sensitivity) package. We study the effect of various geometric parameters such as the uniform segment diameter, the uniform segment length, and the incident angle of the optical wave on the tapered fiber sensor sensitivity for evanescent sensing. Our study shows that high sensitivity of the tapered fiber can be realized by optimizing its parameters. In addition, we design a novel packaging of a tapered-fiber sensor, which can efficiently ensure a uniform stress and reduce the cross sensitivity caused by stress in liquid detection using a tapered fiber sensor. We report the experimental results obtained using this tapered fiber sensor for refractive-index measurements. As the refractive index of liquids varies from 1.417 to 1.423, the measurement results show that the refractive-index sensitivity of the tapered fiber sensor is as high as 4860 nm/RIU.     

Application of multimode fiber optical sensor in optical tomography technology

In this paper, an attempt to use a multimode optical fiber sensor in tomography is made. Two types of lens, one sphere and one cylinderical, are designed for two terminals of the fiber. It solves the problem of insufficient power collection of natural light beam using current fiber with polished terminals. A theoretical analysis of the relationships among the sphere lens radius, the cylinderical lens radius, the refractive index of the fiber is carried out. The relationship between the scanning angles and the number of the optical fibers is experimentally investigated in the air medium.     

Optical biosensor with dispersion compensation

Dispersion limits performance in many optical systems. In surface plasmon resonance (SPR) biosensors, the sensing area is an optical element in which the dispersion depends on the effective refractive index of the biochemical compounds to be measured. We report a method of compensating for wavelength dispersion in SPR biosensors employing two integrated diffractive optical coupling elements in a polymer substrate. The dispersion compensation is achieved over the whole dynamic measurement range and provides a biosensor more robust to wavelength fluctuations than prism-coupler SPR systems. The concept can readily be employed in other types of sensor measuring refractive-index changes.     

Fabrication of single-mode waveguide structure in optical multimode fluoride fibers using self-channeled plasma filaments excited by a femtosecond laser

A permanent structure of a single-mode waveguide in optical multimode fluoride fibers was first fabricated using a self-channeled plasma filament excited by a femtosecond (110-fs) Ti:sapphire laser (_p=800 nm). The photoinduced refractive-index modification in a multimode step-index fluoride glass (ZBLAN) fiber with a 100/110-m core/cladding diameter reached a length of approximately 12–15 mm from the input surface of the optical fiber, with the diameters ranging from 5 to 8 m at input intensities more than 1.0×10¹² W/cm². The graded refractive-index profiles were fabricated to have a symmetric form from the center of a multimode fluoride fiber and a maximum value of the refractive-index change (n) was measured to be 1.3×10^-2. The beam profile of the output beam transmitted through the modified multimode fibers showed that the photoinduced refractive-index modification produced a permanent structure of a single-mode waveguide. PACS 42.55.-f; 42.65.Jx; 42.81.Wg     

Refractive index sensor based on high-order surface plasmon resonance in gold nanofilm coated photonic crystal fiber

We propose a novel kind of wide-range refractive index optical sensor based on photonic crystal fiber(PCF) covered with nano-ring gold film.The refractive index sensing performance of the PCF sensor is analyzed and simulated by the finite element method(FEM).The refractive index liquid is infiltrated into the cladding air hole of the PCF.By comparing the sensing performance of two kinds of photonic crystal fiber structures, a wide range and high sensitivity structure is optimized.The surface plasmon resonance(SPR) excitation material is chose as gold, and large gold nanorings are embedded around the first cladding air hole of the PCF.The higher order surface plasmon modes are generated in this designed optical fiber structure.The resonance coupling between the fundamental mode and the 5 th order surface plasmon polariton(SPP)modes is excited when the phase matching condition is matched.Therefore, the 3 rd loss peaks appear obvious red-shift with the increase of the analyte refractive index, which shows a remarkable polynomial fitting law.The fitnesses of two structures are 0.99 and 0.98, respectively.When the range of refractive indices is from 1.40 to 1.43, the two kinds of sensors have high linear sensitivities of 1604 nm/RIU and 3978 nm/RIU, respectively.