In vivo optical neural recording using fiber-based surface plasmon resonance

We propose an intrinsic optical method for in vivo neural recording using optic fiber-based surface plasmon resonance (SPR) phenomena. The fiber-based SPR method is electrical artifact free, labeling free, and feasible for a portable system compared with conventional in vivo neural recording systems. We simultaneously detected SPR signals and electrical neural activity from the rat somatosensory cortex evoked by electrical stimulation on the forepaw. Pharmacological analysis using a voltage-gated sodium channel blocker confirmed the neural origins of the optical signals. This fiber-based SPR system promises the enhanced ability to record in vivo neural activity for the investigation of neurons and their networks.     

Investigation of dual-channel fiber-optic surface plasmon resonance sensing for biological applications

A dual-channel fiber-optic sensor based on surface plasmon resonance (SPR) for self-referencing refractive-index measurements has been proposed. Most applications of fiber-optic SPR sensors are designed to measure the refractive index of a liquid or gas sample by measuring the signal from a single surface, the sensitivity and stability of which is easily affected by the fluctuation of external environmental conditions. We have designed a dual-channel fiber-optic surface sensor with two independent SPR signals from two areas of the same probe. A prototype sensor was fabricated and characterized. The preliminary experimental results demonstrate the characteristic responses of both SPR signals from two channels that independently correspond to the refractive index changes in the liquid samples with which they are in contact. The design could be extended to a multichannel sensor with further developments. The experimental results confirmed that one channel can be used as a reference sensor that could compensate for unexpected changes in bulk refraction or temperature and develop this sensor as a practicable high-sensitivity biosensing device.     

Low-cost,high performance surface plasmon resonance-compatible films characterized by the surface plasmon resonance technique

A new analytical method based on the surface plasmon resonance (SPR) technique is presented, with which SPR curves for both wavelength and angular modulations can be obtained simultaneously via only a single scan of the incident angle. Using this method, the SPR responses of TiO2-coated Cu films are characterized in the wavelength range from 600 nm to 900 nm. For the first time, we determine the effective optical constants and the thicknesses of TiO2-coated Cu films using the SPR curves of wavelength modulation. The sensitivities of prism-based SPR refractive index sensors using TiO2-coated Cu films are investigated theoretically for both wavelength and angular modulations, the results show that in the case of sensitivity with wavelength modulation, TiO2-coated Cu films are not as good as the Au film, however, they are more suitable than the Au film for SPR refractive index sensors with angular modulation because a higher sensitivity can be achieved.     

基于高斯拟合的光纤型SPR信号的峰值检测算法

光纤型表面等离子共振光谱具有半峰宽较宽,共振峰不尖锐等特征,传统的针对棱镜型SPR光谱的峰值检测算法无法准确定位此类光谱的共振峰值。为了准确计算光纤型SPR光谱的共振波长,提出了一种基于信赖域算法的高斯拟合方法,在拟合的光谱曲线上利用一维搜索的方式确定峰值位置。通过对标准甘油光谱数据的处理,证明高斯拟合法能够适应光纤型SPR光谱的特征,波长计算准确。通过搭建的SPR系统,实验测量了不同浓度下蔗糖溶液的SPR光谱数据,并分别采用加权质心法,追踪质心法和该研究提出的高斯拟合法进行共振波长的计算。结果表明高斯拟合法能够有效提升分辨率,且运算速度较快,有利于工程集成。     

基于光谱解调的对称波导型表面等离子体共振传感研究

表面等离子体共振(SPR)传感系统有角度谱、光谱、强度、相位等解调方式,其中光谱型的(SPR)传感系统因可以使用光纤导光,将传感部分独立出来,可进行远距离传感和现场检测,并能有效缩小系统的体积。对称光波导型(SOW)SPR因金属膜层两边的折射率完全相同,表面等离子体波传播距离更长,穿透深度更深,比传统的SPR系统具有更高的灵敏度和分辨率。对对称波导型(SOW)SPR进行光谱解调研究,以MgF₂-Au-MgF₂结构的SOW-SPR为传感单元,同时以光纤输出的卤素灯为光源, 搭建了一套光谱解调的SOW-SPR检测系统,以不同浓度的葡萄糖溶液对系统折射率分辨率进行测量,得到2.8×10-7 RIU的分辨率。为SOW-SPR系统小型化、现场检测以及远距离探测提出一种可能实现的手段,具有很好的应用前景。     

Optical fiber SPR biosensor with sandwich assay for the detection of prostate specific antigen

We present a new, sensitive, few mode fiber (FMF) surface plasmon resonance (SPR) biosensor with a sandwich assay for the detection of PSA. The side-polished FMF biosensor does not need a polarizer and a thin high-index overlayer. The optical sensitivity of the SPR sensor was determined as 2.5 × 10⁻⁶ RIU. In the SPR PSA sensor, the SPR signals were amplified by a factor of 6 in average over no secondary antibody, using the sandwich assay. The proposed FMF SPR biosensor has great potential for real-time analysis of immune reaction between biomolecules and the advantages of high-sensitivity and label-free detection.     

Coherent optical neural networks and the generalization characteristic

Coherent optical neural-network systems are presented by which we are to realize (1) control of optical neural-network behavior by carrier frequency modulation and (2) frequency-domain multiplexing as a new degree of neural parallelism. In the coherent optical neural network, lightwave carries amplitude, phase, and frequency signals which are processed through optical neural connections consisting of transparency, delay, and optical nonlinear neurons. The neural learning process is realized by adjusting the delay time and the transpar-ency of the optical connections by regarding the carrier frequency as a learning parameter. A simulation experiment demonstrates that the proposed system learns desired output signals depending on the optical carrier frequencies, which leads to the above advantages. It is also found that the generalization characteristics depends on built-in input delays. The generalization quality is discussed from the viewpoint of function approximation or synthesis using sinusoidal basis functions.     

表面等离子共振效应中传统近似理论与薄膜光学理论

指出Kretschmann模型的传统表面等离子共振公式在求解金属薄膜的参量时存在近似性,采用更为严密的薄膜光学理论,通过薄膜膜系的特征矩阵,得出表面等离子体共振衰减曲线.结果表明,表面等离子体共振近似理论与薄膜光学理论得到的共振角及反射率幅度存在差别;采用等高线图,给出了共振角差随着金属介电常量的变化规律.进一步的实验表明,薄膜光学理论所得模拟结果较表面等离子体共振近似理论与实验值吻合地更好,证明薄膜光学理论应用在表面等离子体共振效应要优于常用的近似理论.最后,采用两种理论对表面等离子体共振传感器进行优化设计,结果表明,两种理论所获得的高灵敏度分布区域差异较大,必须采用薄膜光学理论提供更精确的薄膜参量,来优化设计高灵敏度表面等离子体共振传感器.     

Effect of metamaterial layer on optical surface plasmon resonance sensor

In this paper an optical surface plasmon resonance (SPR) sensor with metamaterial for four and five layered structure is studied. The numerical results presented in this paper leads to a significant properties of metamaterials in sensing field. Computed results of SPR sensors using metamaterial are compared with conventional optical SPR sensors for four and five layered structure. It is seen that wider dynamic range or effective range of measurable refractive index increases when metamaterial layer is used. It is also verified that SPR sensor with metamaterial layer can dramatically enhance the resolution and reduce the reflectivity compared with conventional SPR. Validity of the magnetic field results is proved on the basis of smooth match of the fields in the different layers of the proposed optical SPR sensor.     

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。     

光纤SPR湿敏传感器及其共振光谱特性研究

提出并研制了基于光纤SPR传感探针的新型湿敏传感器。首先研究了光纤SPR传感探针对环境湿度变化的敏感特性,在此基础上提出在光纤SPR传感探针表面增覆不同厚度且具有水分子吸附功能的PVA薄膜来实现环境相对湿度的监测。研究结果表明,增覆双层PVA薄膜的光纤SPR传感探针在高湿区具有较好监测效果,其共振强度对应的相对湿度测量灵敏度达到1.59%/%RH,较光纤SPR探针呈现显著提高。而增覆单层PVA薄膜的光纤SPR传感探针在高湿区共振波长对应的相对湿度监测灵敏度达到2.411nm/%RH。此外所提出的新型光纤SPR湿敏探针在PVA薄膜失效后经过特殊工艺处理仍可重复镀膜使用。     

Cross-point analysis for a multimode fiber sensor based on surface plasmon resonance

A novel analysis based on surface plasmon resonance (SPR) with a side-polished multimode fiber and a white-light (halogen light) source is presented. The sensing system is a multimode optical fiber in which half of the core has been polished away and a 40 nm gold layer is deposited on to the polished surface by dc sputter. The SPR dip in the optical spectrum is investigated with an optical spectrum analyzer (OSA). In our SPR fiber sensor, the use of liquids with different refractive indices leads to a shift in the spectral dip in the SPR curve. The cross point (CP) of the two SPR spectra obtained from the refractive-index liquid and the deionized water measurements was observed with the OSA. The CP is shifted sensitively in wavelength from 630 to 1300 nm relative to a change in the refractive index of the liquid from 1.34 to 1.46. High sensitivities of 1.9 x 10(-6) refractive-index units (RIUs) in the range of the refractive index of the liquid from 1.40 to 1.44 of 5.7 x 10(-7) RIUs above the value of 1.44 are proposed and demonstrated in our novel SPR analysis.     

Optical cavity coupled surface plasmon resonance sensing for enhanced sensitivity

A surface plasmon resonance (SPR) sensing system based on the optical cavity enhanced detection tech-nique is experimentally demonstrated. A fiber-optic laser cavity is built with a SPR sensor inside. By measuring the laser output power when the cavity is biased near the threshold point, the sensitivity, defined as the dependence of the output optical intensity on the sample variations, can be increased by about one order of magnitude compared to that of the SPR sensor alone under the intensity interrogation scheme. This could facilitate ultra-high sensitivity SPR biosensing applications. Further system miniaturization is possible by using integrated optical components and waveguide SPR sensors.     

Performances of different metals in optical fibre-based surface plasmon resonance sensor

The capability of various metals used in optical fibre-based surface plasmon resonance (SPR) sensing is studied theoretically. Four metals, gold (Au), silver (Ag), copper (Cu) and aluminium (Al) are considered for the present study. The performance of the optical fibre-based SPR sensor with four different metals is obtained numerically and compared in detail. The performance of optical fibre-based SPR sensor has been analysed in terms of sensitivity, signal-to-noise (SNR) ratio and quality parameter. It is found that the performance of optical fibre-based SPR sensor with Au metal is better than that of the other three metals. The sensitivity of the optical fibre-based SPR sensor with 50 nm thick and 10 mm long Au metal film of exposed sensing region is 2.373 μm/RIU with good linearity, SNR is 0.724 and quality parameter is 48.281 RIU^− 1. The thickness of the metal film and the length of the exposed sensing region of the optical fibre-based SPR sensor for each metal are also optimized.     

An Approximate Theoretical Model of Surface Plasmon Resonance Optical Waveguide and Fibre-optic Sensors

Optical surface plasmon resonance (SPR) excitation can be theoretically depicted and discussed using Fresnel’s equations. However, Fresnel’s equations cannot explicitly give expressions to reflect the characteristics of SPR systems, especially in SPR optical waveguide and fibre-optic sensors. In this paper a mathematical model based on the approximation proposed by Kretschmann in bulk optics is presented to describe the characteristics of SPR optical waveguide and fibre-optic sensors. The results show that the model keeps high accuracy when used in the area close to the minimum reflection, at which the resonance condition is achieved. This model can be used to analytically estimate the performance of SPR optical waveguide sensors, and SPR fibre-optic sensors in meridional rays approximation.     

基于表面等离子体共振原理的空芯光纤传感器

设计了一种基于表面等离子体共振原理,使用空芯光纤作为光波导、外表面镀金属膜的光学材料圆柱体作为探头的新型折射率传感器。通过建立光学模型进行分析,在理论上推导出了这种传感器的传输光谱损耗公式,并针对该传感器在不同的光纤长度、探头材料、检测物质折射率等参数设置下的检测性能进行了分析,获得了各种参数对其性能的影响。由于该传感器可针对不同折射率的检测物质灵活地更换合适探头材料,相对于传统的表面等离子体共振光纤传感器,在易用性和性价比等方面具有更好的应用价值。     

基于异步延迟采样的光通信性能监测方法

基于异步延迟采样和人工神经网络统计学习提出了一种光通信性能监测方法。通过对高速光信号进行异步延迟采样,获得信号二维幅度直方图,然后提取其中特征参数并对人工神经网络进行训练,最后以人工神经网络的预测输出实现对光信号损伤的监测。构建10 Gb/s非归零码开关键控,40 Gb/s光学双二进制码和归零码差分移相键控光通信仿真系统,并对光信噪比、色散和偏振模色散损伤进行监测。仿真结果表明,所提方法对被监测光信号的速率、码型调制格式透明,可同时准确监测多种并存的传输损伤,损伤参数监测误差小于5%。该方法具有电域处理带宽要求低、采样机制简单的特点,适用于分布式在线光性能监测。     

用扫描近场光学显微镜技术研究金膜表面等离体子共振

表面等离体子波(SPW)可与入射光横磁波极化能量耦合并被共振激发,这种现象被称为表面等离体子共振现象(SPR)。主要利用扫描近场光学显微镜(SNOM)技术和表面等离体子共振现象技术相结合,来研究金膜表面等离体子共振。设计并建立了结构独特的新型Kretschmann型表面等离体子共振现象耦合装置,同时又设计了具有厚度梯度的表面等离体子的制备方法。在此基础上,测量了改变入射角条件下的表面等离体子共振曲线,测得该装置的等离体子共振角灵敏度为1°。并且对金膜表面进行表面等离体子共振条件下的扫描近场光学显微成像。实验结果表明,在共振时金膜表面的扫描成像比不共振时清晰,而且增加了很多细节。应用表面等离体子共振现象技术将可以明显提高扫描近场光学显微镜的信噪比、分辨力等性能。     

High-Sensitivity Sensor Based on Surface Plasmon Resonance Enhanced Lateral Optical Beam Displacements

We present a new optical sensor based on surface plasmon resonance （SPIt） enhanced lateral optical beam displacements. Compared with the traditional SPIt methods, the new method provides higher sensitivity to the sensor system. Theoretical simulations show that the refractive index （RI） detection sensitivity of the SPR sensor based on the displacement measurement has a strong dependence on the thickness of the metal film. When the optimal thickness of the metal film is selected, the RI resolutlon of the SPIt sensor is predicted to be 2.2 × 10^-7 refractive index units （RIU）. Furthermore, it is found that the incidence angle can be used as a parameter to adjust the operating range of the sensor to different refractive index ranges.