Plasmonic refractive index sensor based on the combination of rectangular and circular resonators including baffles

We numerically designed a plasmonic refractive index sensor with high sensitivity and tunable optical feature based on two metal-insulator-metal bus waveguides connecting with the central-coupled rectangular and circular ring resonators, including silver (Ag) baffles. In the design process, Ag baffles' influence on transmittance spectrum, magnetic and electric field distributions, surface power flow intensity, energy streamlines, and sensor performance are investigated using the finite element method. The proposed structure can use as a high precision plasmonic refractive index sensor for refractive index in the increment range of 0.01. The maximum sensitivity can reach 3400 nm/RIU (RIU is a refractive index unit), which remarkably increases the sensitivity of 1.36 times compared to the case without Ag baffles. Besides, the figure of merit and quality factor can achieve 36.00 and 42.28, respectively. The sensitivity and figure of merit can be increased by adding the Ag baffles in the proposed plasmonic sensor system, generating an additional gap plasmon resonance mode that cannot find in a typical case.     

Highly integrated plasmonic sensor design for the simultaneous detection of multiple analytes

Herein, a highly integrated plasmonic sensor based on a multichannel metal-insulator-metal waveguide scheme for the simultaneous detection of multiple analytes is proposed. The numerical study is conducted via the finite element method based on commercially available software COMSOL. The sensor design is highly sensitive which can detect a minute change in the refractive index of the analyte. In this study, we have used the refractive index values of three different concentrations of ethanol and d-glucose solution to determine the sensor performance. It is observed that the device is highly sensitive as the operational wavelength lies in the deep shortwave infrared region. The numerically calculated sensitivity as high as 1948.67 nm/RIU is obtained for the cavity length of 325 nm which can be further improved by designing the device with large cavities. We believe that the proposed study is beneficial for the realization of the highly integrated plasmonic sensors for the lab-on-chip operations.     

Reflex optical sensor based on dual metal gratings with high angular sensitivity

An interesting reflection phenomenon in a dual metal grating (DMG) structure is studied, which is related to the competition between Fabry-Prot (F-P) resonance effect and evanescent-field coupling effect inside the gap between the two composing single metal gratings. This competition leads to high angular sensitivity in response to the refractive index variation of the sample solution in the gap. A reflex optical sensor with high sensitivity based on DMG for detecting the change in refractive index is proposed and its performance theoretically is discussed.     

金属纳米结构对光谱响应及折射率灵敏度的影响

推导了任意形状金属纳米结构对复杂环境折射率的局域表面等离子体共振(LSPR)光谱响应的解析解,给出了体折射率和局部折射率灵敏度公式,并进行了详细的理论分析和数值验证。结果表明,金属纳米结构的光谱响应与被分析物厚度呈指数增长关系,并与被分析物的折射率、敏感层厚度、金属纳米结构的材料和形状等因素有关。被分析物折射率越高,光谱响应越大。敏感层越厚,局部折射率灵敏度越差。同时,尖锐的金属纳米结构形状可以获得更大的体折射率灵敏度。对金属纳米结构光谱响应及折射率灵敏度的研究对制作高灵敏度LSPR传感器具有重要的指导意义。     

Independently tunable dual resonant dip refractive index sensor based on metal—insulator—metal waveguide with Q-shaped resonant cavity

A plasmonic resonator system consisting of a metal—insulator—metal waveguide and a Q-shaped resonant cavity is proposed in this paper. The transmission properties of surface plasmon polaritons in this structure are investigated by using the finite difference in time domain (FDTD) method, and the simulation results contain two resonant dips. The physical mechanism is studied by the multimode interference coupled mode theory (MICMT), and the theoretical results are in highly consistent with the simulation results. Furthermore, the parameters of the Q-shaped cavity can be controlled to adjust the two dips, respectively. The refractive index sensor proposed in this paper, with a sensitivity of 1578 nm/RIU and figure of merit (FOM) of 175, performs better than most of the similar structures. Therefore, the results of the study are instructive for the design and application of high sensitivity nanoscale refractive index sensors.     

Highly sensitive photonic crystal fiber biosensor based on titanium nitride

A highly sensitive surface plasmon resonance photonic crystal fiber (PCF) biosensor based on Titanium Nitride (TiN) as a new alternative plasmonic material is proposed and analyzed. The TiN has high stability, high conductivity, and corrosion resistance which make it an ideal material for nanofabrication. The suggested biosensor is analyzed by full vectorial finite element method with perfectly matched layer as boundary conditions. In this paper, the biosensor geometrical parameters are studied to achieve high sensitivity for both polarized modes. A refractive index sensitivity of 7700 and 3600 nm/RIU for quasi-transverse electric and quasi transverse magnetic modes, respectively, are obtained. Additionally, the reported biosensor could be used for detecting an unknown analyte refractive index ranging from 1.32 to 1.34 with a high linearity. Further, the proposed biosensor structure is easy for fabrication using standard PCF fabrication current technologies.     

电压调控多种金属膜波导特性研究

采用自由空间耦合的方法,激发双面金属包覆波导中的超高阶导模,通过在双面金属包覆介质波导的两个金属膜上加不同的电压,改变导波层铌酸锂的厚度和折射率,得到不同参数下的衰减全反射谱,从而验证超高阶导模的偏振不灵敏性及对导波层厚度和折射率十分灵敏的特殊性质,实验结果与理论相吻合。比较相同条件下反射率的变化,得到铝包覆波导的灵敏度要高于金包覆波导。所得结果对集成光电子器件的研制有一定的参考价值。     

Plasmonic properties of silver nanocube monolayers on high refractive index substrates

Extinction spectra of nanocubes supported by a symmetry breaking dielectric substrate are very different from those in solution. In this work, we varied the refractive index of the substrate in order to optimize the refractive index sensitivity (RIS) of supported silver nanocube monolayers. We found that on thin (5?C7?nm) silicon films, the RIS is characterized by the figure of merit (FOM) for the quadrupolar plasmonic mode as high as 5.0, making silicon supported silver nanocube monolayers a promising sensing platform.     

基于金属孔阵列的聚酰亚胺薄膜太赫兹探测

优化设计了多种不同孔径和形状的太赫兹波段的亚波长金属孔阵列结构,结合超薄低折射率的聚酰亚胺（PI）薄膜,探索了太赫兹时域光谱技术对超薄低折射率的探测灵敏性。利用飞秒微加工技术制备了一系列亚波长金属孔阵列结构,利用太赫兹时域光谱技术测试了阵列结构的反射波谱,获得了强烈的反射共振现象。然后在亚波长金属孔阵列结构背面叠加PI薄膜,结果表明太赫兹反射峰出现了显著低频移动现象。利用这一现象,实现了低至10 m的PI薄膜的有效探测,说明亚波长金属孔阵列结构在太赫兹传感领域对检测超薄低折射率薄膜材料有极强敏感性。收稿日期:; 修订日期:     

Silver Nanocube Aggregates in Cylindrical Pores for Higher Refractive Index Plasmonic Sensing

We report on silver nanocubes (AgNCs) infiltrated into cylindrical nanopores of porous alumina membranes (PAM) with an outstanding chemical sensitivity based on refractive index sensing (RIS) measurements. Numerical simulations performed using the finite‐difference time‐domain (FDTD) method suggested that the enhanced sensitivity is based mainly on the inter‐pore coupling plasmonic effect. This effect is related to plasmonic amplification based on localized surface plasmon resonance (LSPR) coupling between AgNCs located at the pore walls of neighboring cylindrical pores and separated by a nanoscale wall. Results are discussed for different aggregation scenarios ranging from individual nanocubes through pentamers on a flat glass surface, a flat alumina surface, and a concave local shape representing the experimental conditions. An experimental RIS sensitivity of about 770 nm per refractive index unit was found to be more than an order of magnitude higher for silver nanocube aggregates within cylindrical pores than that observed for ordinary planar substrates.     

Arrays of doped and un-doped semiconductors for sensor applications

This numerical investigation proposes to use a lamellar grating of doped semiconductors as the active region of a nanoplasmonic biosensing device. Working with highly doped semiconductors instead of a metal allows controlling the value of the plasma frequency. It is possible to reach a plasma frequency close to the range of detection of the sensor to improve its sensitivity. A?red shift of the plasmonic resonance of 10.2?nm for a 10^?2 refractive index unit increase can be achieved.     

High-performance refractive index sensor based on guided-mode resonance in all-dielectric nano-silt array

We propose a high-quality refractive index sensing by utilizing the characteristic guided-mode resonance (GMR) excited in a simple one-dimensional all-dielectric nano-slit array. We demonstrate a figure of merit up to 12000, which is higher than that achieved in most plasmonic refractive index sensors. We show that high-quality sensing performance can be sustained over a broadband range in near infrared region with relatively large variations in both grating depth and angle of incidence. Such a GMR-based all-dielectric sensing device with the ease of fabrication is expected to hold great promise for realizing broadband refractive index sensors with high performance and compactness.     

Characteristics analysis of hybrid plasmonic waveguide for low-loss lightwave guiding

It has been experimentally demonstrated that a low-loss guided hybrid mode is supported if a metal strip is embedded in a low index polymer layer surrounded by two high index slabs. In this paper, further numerical analyses on the guided hybrid modes are reported to fully elucidate the characteristics of the hybrid plasmonic waveguide. For a one-dimensional slab structure with a metal film of infinite width, simulation results exhibit that low-loss guided hybrid modes are associated with surface plasmon modes and dual dielectric slab modes. The optical properties of the guided modes are improved by increasing the field intensity which is confined into lossless dielectric layers by decreasing the metal film thickness and increasing the refractive index and thickness of the high-index slabs. The finite element method is used to investigate the lateral mode confinement of the optical guided modes by the corresponding metal strip. By reducing the metal film width, the guided modes are confined in the plane transverse to the direction of propagation and the characteristics are significantly improved. The hybrid plasmonic waveguide can be exploited for long-range propagation-based application such as optical interconnection.     

A novel plasmonic refractive index sensor based on gold/silicon complementary grating structure

A novel complementary grating structure is proposed for plasmonic refractive index sensing due to its strong resonance at near-infrared wavelength.The reflection spectra and the electric field distributions are obtained via the finite-difference time-domain method.Numerical simulation results show that multiple surface plasmon resonance modes can be excited in this novel structure.Subsequently,one of the resonance modes shows appreciable potential in refractive index sensing due to its wide range of action with the environment of the analyte.After optimizing the grating geometric variables of the structure,the designed structure shows the stable sensing performance with a high refractive index sensitivity of 1642 nm per refractive index unit(nm/RIU)and the figure of merit of 409 RIU^-1.The promising simulation results indicate that such a sensor has a broad application prospect in biochemistry.     

三角形银纳米柱阵列传感乙醇气体方法研究

提出了一种基于金属纳米结构局域表面等离子体共振光谱的有机气体的传感方法.通过时域有限差分法设计了一种具有较高折射率灵敏度的三角形纳米柱阵列,并利用纳米球光刻法进行了制作.对乙醇蒸汽的传感实验结果证明,所制作的三角形银纳米柱对乙醇分子浓度非常敏感,其探测灵敏度达到24ppm/nm.该金属纳米结构传感有机气体的方法有望应用于环境监测等方面.     

Numerical analysis of a photonic crystal fiber based on two polarized modes for biosensing applications

This paper presents a theoretical study on a photonic crystal fiber plasmonic refractive index biosensor. The proposed photonic crystal fiber sensor introduces the concept of simultaneous detection with the linearly polarized and radially polarized modes because the sensing performance of the sensor based on both modes is relatively high, which will be useful for selecting the modes to make the detection accurately. The sharp single resonant peaks of the linearly polarized mode and radially polarized mode, are stronger and more sensitive to the variation of analyte refractive index than that of any other polarized mode in this kind of photonic crystal fiber. For linearly polarized mode and radially polarized mode, the maximum sensitivities of 10448.5nm per refractive index unit and 8230.7nm per refractive index unit can be obtained, as well as 949.8 and 791.4 for figure of merits in the sensing range of 1.33-1.45, respectively. Compared with the conventional Au-metalized surface plasmon resonance sensors, our device is better and can be applied as a biosensor.     

All optical switch based on Fano resonance in metal nanocomposite photonic crystals

We investigate the potential of plasmonic resonance in metal nanocomposite materials for the design of photonic crystal all optical switches by numerical methods. We study the absorption effect of the plasmonic resonance on the Fano resonances of one dimensional photonic crystal slabs covered by a metal nanocomposite layer. It is shown that the absorption reduces the contrast of the Fano resonances. However, for adequate metal nanoparticle concentrations it is possible to achieve both sufficiently sharp Fano resonance and strong Kerr nonlinearity, which provides a suitable condition for the design of high contrast and low threshold switches.     

Local plasmon excitations in one-dimensional array of metal nanowires for sensor applications

Optical properties of a one-dimensional periodic array of subwavelength metal nanowires in the regime of local plasmon excitation are investigated experimentally and theoretically. Both gas and liquid sensing by one-dimensional gold nanowires on a glass substrate produced by holographic lithography are demonstrated experimentally. The obtained spectral sensitivity of a local plasmon sensor to the refractive index of the environment is found comparable to that of a surface plasmon polariton sensor based on the grating coupler effect. The influence of nanowire shape on spectral sensitivity is studied theoretically in a differential formalism framework using a curvilinear coordinate transformation for triangular, trapezoidal, and rectangular cross sections of the nanowires. For nanowires with trapezoidal cross section, theoretical calculations for the spectral sensitivity to variation of the refractive index of the environment agree well with experimental data.     

Highly sensitive refractometer with a photonic-crystal-fiber long-period grating

We present highly sensitive refractometers based on a long-period grating in a large-mode-area photonic crystal fiber (PCF). The maximum sensitivity is 1500 nm/refractive index unit at a refractive index of 1.33, to our knowledge the highest reported for any fiber grating. The minimal detectable index change is 2 x 10(-5). The high sensitivity is obtained by infiltrating the sample into the holes of the PCF to give a strong interaction between the sample and the probing field.     

Analysis and applications of nanocavity structures used as tunable filters and sensors

This paper reports on a novel design for a tunable filter and plasmonic sensor based on the metal–insulator–metal waveguide with a nanocavity resonator. Simulation results show that as a one-channel filter, the resonance wavelengths show a linear red-shift with an increase in nanocavity length with a slope of 1742 nm/μm and a nonlinear blue-shift with an increase in nanocavity width, respectively. A two-channel filter can be realized using two nanocavities and the arrangement of the two nanocavities with respect to the waveguide and the value of the distance between the nanocavities has only a marginal effect on the filter notch wavelength. Finally, both in-slit and out-slit refractive index plasmonic sensors are investigated with a sensitivity of 710 nm/RIU and 250 nm/RIU, respectively.