Improve the refractive index sensitivity of gold nanotube by reducing the restoring force of localized surface plasmon resonance

The core refractive index sensitivity of a gold nanotube was investigated by calculating the shift of local surface plasmon resonance (LSPR). It was found that the core refractive index sensitivity can be improved by reducing the wall thickness or the surrounding refractive index. The sensitivity increases exponentially with decreasing wall thickness, but increases linearly with decreasing surrounding refractive index. This multi-factor controlled sensitivity of gold nanotube enlarges the ability of optimizing the refractive index sensors. The physical origin of this tunable refractive index sensitivity of gold nanotube was also investigated based on the plasmon hybridization and repulsive effects on the restoring force of plasmon oscillation. This physical mechanism can be used for designing core-shell metallic nanostructures for effective LSPR chemical and biological sensing.     

微纳米高折射率涂敷层对长周期光纤光栅传输谱特性的影响

基于模式耦合理论,通过求解给定参数的覆盖高折射率微纳米涂敷层长周期光纤光栅( LPFG)的频谱,分析了四层模型LPFG中微纳米高折射率涂敷层对其传输谱特性的影响。研究结果表明：通过设计涂覆层厚度、涂覆层折射率变化范围以及LPFG包层厚度等参数,包层模将进入高折射率微纳米涂敷层中进行传输,在LPFG传输谱出现模式迁移现象;随着涂覆层折射率的增大,谐振峰波长向短波长方向漂移;LPFG包层半径越小,谐振峰波长对涂覆层折射率变化的响应灵明度越高。     

Sensitivity optimization of surface plasmon sensors for detection of intermediate layers

A sensitivity optimization method for the detection of an intermediate layer using a surface plasmon sensor is presented. The dependence of detection sensitivity on distance from the metal surface and the average refractive index over the sensing region are considered. Based on the calculated results, the sensitivity for detecting an intermediate layer in a multilayered sample is determined by varying the refractive index and thickness of each layer. It is shown that, in particular cases, controlling the refractive index and thickness increases the detection sensitivity. The proposed method is useful for designing multilayered samples.     

LiNbO3棱镜耦合双金属薄膜表面等离子共振传感器

高折射率铌酸锂(LiNbO3)(2.202)为棱镜耦合激发的角度调制型表面等离子共振传感器,利用反射率公式优化单层银膜、金膜和双层银/金膜传感器薄膜的厚度,分别计算了优化厚度的传感器在检测样品折射率为1.330时的共振角、灵敏度、峰值半宽度(FWHM)和品质因数(FOM),理论计算表明:双层金属薄膜,随着金膜厚度的增加,传感器灵敏度增加,但峰值半宽度增加,品质因数下降.综合考虑,选择银/金(41/5)优化组合,传感器品质因数为优化的单层金膜(47 nm)传感器品质因数的2倍以上,另外,与常用的BK7玻璃棱镜耦合相比,LiNbO3棱镜耦合具有较大的样品动态检测范围.优化厚度的传感器实验检测糖水浓度表明:糖水浓度与共振角为线性比例关系.     

一种新型结构长周期光纤光栅光谱特性研究

基于长周期光纤光栅(LPFG)包层有效折射率与包层半径、折射率和环境折射率的良好相关性,提出一种LPFG的新颖结构。利用传输矩阵法和三包层光纤的色散方程对其建模,mathcad15计算软件进行数值仿真和模拟。得到新型结构LPFG谐振峰发生分裂,即一个透射峰分裂为两个;两个分裂峰谐振波长间距随着腐蚀段包层半径的减小或填充材料厚度的增大而增加,模式越高增加越快;同时分裂峰间距在填充材料折射率小于1.4和大于1.48时基本不变,而在1.4和1.48之间分裂峰间距变化显著,在1.44附近达到极值。此种结构LPFG设计上的特殊性即可弥补半腐蚀LPFG容易断的不足,又可通过填充敏感材料且利用分裂峰间距定标而提高气体或液体浓度传感灵敏度。     

Searching for optimal sensitivity of single-mode D-type optical fiber sensor in the phase measurement

To improve the sensitivity of a single-mode D-type optical fiber sensor, we selected a D-type optical fiber sensor with 4 mm long and 4 μm core thickness made of a single-mode fiber, a Au-coating on the sensor with a thickness range of 15–32 nm, a light wavelength of 632.8 nm, and an incident angle of 86.5–89.5° for different refractive index (1.33–1.40) sensing. These simulations are based on the surface plasmon resonance (SPR) theory using the phase method which shows that the sensitivity is proportional to the refractive index, Au film thickness and lower incident angle on the sensing interface. The sensitivity is higher than 4000 (degree/RIU), and the resolution is better than 2.5 × 10⁻⁶(RIU) as the minimum phase variation is 0.01°. This device is used to detect the refractive index or gas or liquid concentration in real-time. The proposed sensor is small, simple, inexpensive, and provides an in vivo test.     

Unsupervised urban area extraction from SAR imagery using GMRF

A new method is proposed to extract urban areas from SAR imagery using two different Gaussian Markov Random Field (GMRF) models. Firstly, by making an initial segmentation by a watershed algorithm, we adopt a particular GMRF model proposed by Descombes et al. (the model is called RGMRF model, distinguished from the conventional GMRF model) to acquire urban areas. In the first model a part of the urban areas from the SAR image is extracted with some missing detection. Then, taking the first result as a training sample, we use the conventional GMRF model to redo the extraction. In the second model a larger area is detected including all urban areas with some false detection. Finally, we fuse the two results using a region-growing algorithm to form the final detected urban area. Experimental results show that the proposed method can obtain accurate urban areas delineation. The text was submitted by the authors in English.     

薄包层长周期光纤光栅的折射率传感特性

长周期光纤光栅(LPFG)可用于折射率传感,同时利用折射变化可以实现谐振波长的调谐.不同的光纤包层半径和光栅周期对折射率灵敏度有较大影响.利用光波导的耦合模理论分析了LPFG的折射率传感特性,给出LPFG的折射率灵敏度的解析表达式,给出了利用不同包层模时的折射率灵敏度.利用三层介质光纤的纤芯模本征方程计算了薄包层LPFG的折射率灵敏度.结果表明,基于不同包层模的LPFG的谐振波长随折射率的变化有红移,也有兰移;基于低阶模序包层模的LPFG,折射率灵敏度较小,中间模序最大,而高阶模序则较大,薄包层LPFG对折射率具有更大的灵敏度.     

Optical fiber pH sensor based on lossy-mode resonances by means of thin polymeric coatings

This work describes the fabrication of an optical fiber sensor with spectral response to pH based on the deposition of a thin polymeric coating on an optical fiber core. If the thin polymeric coating has a high refractive index real part and a non-null imaginary part, this permits a coupling of light to the modes guided in the polymeric coating originating optical resonances. These resonances are named by some authors as lossy-mode resonances (LMR) or guided-mode resonances. Moreover, the location of the resonances in the optical spectrum varies as a function of the coating thickness and refractive index. Hence, the utilization of the well-known poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) pH sensitive polymeric coating that presents a variation of the thickness with the pH of the solution (known as swelling/deswelling behaviour) permits the fabrication of optical fiber pH sensors based on wavelength detection. The fabrication of ready-to-use devices requires considering several aspects such as the adequate polymeric coating thickness or the selection of the resonance to be monitored. As a result, LMR-based optical fiber pH sensors with accuracy of ±0.001 pH units and an average sensitivity of 0.027 pH units/nm within the range between pH 3 and pH 6 have been obtained after an adequate design.     

Characterization of optical fiber long period grating refractometer with nanocoating

In this work is studied the response of optical fiber long period grating (LPG) to changes of the refractive index of the external media relatively to variations of wavelength and in transmission. The response of the LPG to refractive index greater and lesser than to cladding is investigated. A nanolayer was deposited onto the fiber to increase the sensitivity of the LPG to refractive index of the external media higher than cladding. The film modifies the rates of effective modes of cladding, thus improving the response of the changes in the refractive index of the external media higher than that in the refractive index of the cladding (n_cl ≈ 1.457). The Langmuir-Blodgett technique was used for the deposition of the nanolayer.     

Absorption-based fiber optic surface plasmon resonance sensor: a theoretical evaluation

In this paper, an optical absorption based fiber optic surface plasmon resonance (SPR) sensor has been studied theoretically. The theoretical treatment is based on Kretschmann’s SPR theory and the Lorentz model that expresses a damped harmonic oscillator is included in the treatment for optical absorption in the sensing layer. The optical source considered is an un-polarized collimated beam. The light is coupled to the fiber using a microscope objective that focuses the beam at the center of the input face of the fiber. The effects of the parameters related to the sensing region, the light source and the optical fiber on the sensitivity and the operating range of the SPR sensor have been studied with the help of numerical calculations and computer simulations. It has been found that the excitation frequency in absorption-based fiber optic SPR sensor is an important parameter. The sensitivity is better for the lower off-resonance excitation frequency. The sensitivity and the operating range of the sensor are better for large value of the core diameter. The optimization of numerical aperture of the fiber, film thickness and the length of the sensing region is required to achieve the maximum sensitivity. Further, the increase in the extinction coefficient of the sample increases the sensitivity of the sensor while the decrease in the width of its absorption spectrum increases the sensitivity. The sensitivity and the operating range of the sensor are better for small values of the refractive index of the absorbing sample.     

Application of astigmatic method and snell’s law on the thickness and refractive index measurement of a transparent plate

In this study, a thickness and refractive index measuring system for the transparent plate has been proposed. The measuring system is composed of an astigmatic measurement module and a light spot measurement module using a DVD optical pickup, a laser diode and a quadrant photodiode detector. Both of the thickness and refractive index of a transparent plate are converted into the focusing error of DVD pickup based on astigmatic method and the light spot displacements based on snell’s law in our proposed system. The thickness and the refractive index are simultaneously calculated by means of two nonlinear formulas. The accuracy of the proposed system is 99 % verified by a height Gauge and the refractive index by the TF-166.     

基于Ag纳米粒子的LSPR传感器装置设计与实现

设计了一种集原位芯片制备和在线检测于一体的局域表面等离子体共振(LSPR)生物传感器装置,减少了检测过程中芯片移动产生的误差,并实现了小型化、在线化、简易化的目标。在该装置上利用电沉积法制备了Ag纳米粒子的LSPR芯片,实验测试结果表明:氧化铟锡(ITO)层厚度为23±5 nm时,在-1.4 V电位,制得折射率灵敏度为246 nm/RIU的LSPR芯片。     

偏振控制光强调制型SPRi传感器的高灵敏检测研究

在偏振控制光强调制型SPRi传感器中,使用真实液体消光的方法实验调节困难,测量灵敏度低,线性度差.为此,提出无需真实液体消光,并将消光折射率左移的方法.首先,对在测量起点(即纯水)消光的传统方法进行光学参数的最优值仿真及其加工和调节误差仿真,结果表明,误差会引起SPRi曲线最低点在折射率轴上的左右偏移,从而影响传感器性能.接着,将消光折射率左移至1.325处,并仿真其光学参数的最优值.实验表明,与前者相比,1.325消光方法中存在的误差不会使测量曲线出现非单调的情况,此时的测量灵敏度高,线性度好,折射率分辨率达到1.85×10-6 RIU,对应NaCl溶液的检出限为35 mg/L.上述方法提高了误差存在时SPRi传感器的适用性,可以实现微量水溶液样品的高灵敏及高通量检测.     

SPR传感芯片的理论与实验研究

针对光纤SPR(表面等离子体共振)传感器制作工艺复杂的问题,提出了一种光纤先固定后部分镀膜的SPR传感芯片的制作方法.依据电磁场和射线理论,分析并讨论了此种波长调制部分镀膜SPR传感芯片的工作原理,采用MEMS制作工艺对探测光纤进行封装固定以后,再对光纤进行部分镀膜,其结构简单,工艺性好,易于实现批量化.最后,搭建了一套基、于波长检测的光纤SPR测试系统对其进行测试.实验结果表明:在折射率范围为1.33～1.36时,共振波长同折射率具有良好的线性关系,光谱仪分辨率为0.1 m时,其分辨率可达到3×10-5折射率单位.     

Performance of integrated optical microcavities for refractive index and fluorescence sensing

The performance of a novel sensor based on an integrated optical (IO) disk microcavity (MC) is theoretically studied. The MC is a resonant waveguide structure in which multiple interference of a guided mode occurs. At resonance, the MC is extremely sensitive to refractive index changes and it sustains locally enhanced optical field. Therefore, the MC is naturally suitable as an extremely responsive sensor for measuring minute changes in refractive index and/or fluorescence of an analyte. Combination of multiple interference and extremely small sampling volume (few femtoliters) provides unique sensitivity of the MC device. A factor of 9 increase in fluorescence sensitivity versus waveguide sensor is anticipated. Provided shot-noise limited detection, the refractive index resolution down to 10⁻⁹ is feasible with the MC sensor, which exceeds that of the straight waveguide interferometer by the order of magnitude. MC-sensors can be combined into arrays providing high throughput detection of both labeled and non-fluorescent biological species.     

CO-sensing properties of hafnium oxide thin films prepared by electron beam evaporation

Thin films of hafnium oxide were deposited by electron beam evaporation. The effects of the film thickness and preparation conditions (films prepared on the heated substrate with or without the presence of oxygen environment during deposition) on the optical and carbon monoxide sensing properties of the films were studied. The films were characterized using X-ray diffraction and X-ray photoelectron spectroscopy and optical spectroscopy techniques. Films deposited on unheated substrates were amorphous, whereas those deposited on heated substrates showed a mixture of amorphous and polycrystalline structure. It was found that the sensitivity of the films to CO increased with the thickness and the porosity (as reflected by the refractive indices) of the films.     

基于EFAST方法的SEBS模型参数全局敏感性分析

应用高效、稳健的EFAST方法,以黑河流域盈科绿洲站为例,从3个方面对SEBS模型的参数敏感性进行了分析:分别以感热通量(H)、潜热通量(λE)、蒸发比(fr)作为SEBS模型的输出结果,分析其对12个输入参数的敏感性;利用气象数据驱动模型,分析H、λE和fr对6个地表特征参数的敏感性;分析了参数取值范围对敏感性分析结果的影响。研究结果表明:H、λE与fr都对参考高度处的气温和风速、地表温度以及植被特征参数的敏感性较高。参数间相互作用对H、λE的间接影响很小,而对fr的影响较大。当气象输入参数确定时,6个地表参数中地表温度对模型输出的直接贡献最大,其主敏感度指数接近0.6。参数采样范围不同时,模型输入参数的敏感性表现不同。     

贵金属纳米颗粒LSPR现象研究

利用离散偶极近似(Discrete Dipole Approximation,DDA)算法仿真分析了纯金,纯银以及金银核壳结构的纳米颗粒的LSPR(Localized Surface Plasmon Resonance)消光光谱以及其波峰随外部介质折射率的变化情况,与实验相符。发现光谱波峰位置的变化与折射率成线性关系,而且金银核-壳结构的折射率灵敏度大于银纳米颗粒的灵敏度;而银纳米颗粒的灵敏度大于金纳米颗粒的灵敏度。     

Use of a low refractive index prism in surface plasmon resonance biosensing

A way to improve the angular sensitivity of surface plasmon resonance (SPR) biosensor by tuning the resonance position to a higher incident angle region using a lower refractive index glass prism is described in this paper. A novel effective 3-layer (E3L) model is described to transform a multiple layer biosensor configuration in context of SPR condition. The E3L model supports the use of a low refractive index prism for biosensing. The performance of the sensor in immunosensing is checked for two glass prisms of different refractive index materials. The experimental results showed an enhancement in the amount of resonance angle shift of the immunosensor for the lower refractive index glass prism.