Plasmonic waveguiding in a hexagonally ordered metal wire array

We propose the inclusion of a structured pattern of nanoscale metal wires in a silica fiber to form a symmetric plasmonic waveguide. The surface plasmon polariton modes within the waveguide are studied by varying the wire diameter and spacing. Simulation results show that hybridization of the single-wire mode and the gap plasmon mode can yield a hybrid mode with optimum propagation lengths comparable to those reported for other structures but with better light confinement. The fiber can be easily doped with a gain material to offset the loss so that the resultant waveguide will be useful for integration with electronic circuits at nanometer dimensions.     

Plasmonic nanoloop array antenna

In this Letter, we create an optical nanoantenna array composed of parasitic plasmonic loops that can enhance radiation characteristics and direct the optical energy successfully. Three metallic loops inspired by the concept of the Yagi-Uda antenna are optimized around the region where they feature high scattering performance to control the radiation beam. The loop geometry, when compared to the dipole configuration, has the benefit of using the available aperture in an effective way to provide higher directivity. The angular emission of the nanoloop array antenna is highly directive, and a directivity of 8.2 dB for upward radiation is established.     

Plasmonic Brewster angle: broadband extraordinary transmission through optical gratings

Extraordinary optical transmission through metallic gratings is a well established effect based on the collective resonance of corrugated screens. Being based on plasmonic resonances, its bandwidth is inherently narrow, in particular, for thick screens and narrow apertures. We introduce here a different mechanism to achieve total transmission through an otherwise opaque screen, based on an ultrabroadband tunneling that can span from dc to the visible range at a given incidence angle. This phenomenon effectively represents the equivalent of Brewster transmission for plasmonic and opaque screens.     

Plasmonic couplers with metal nonlinearities

Usually nonlinear response of metals is neglected in the study of plasmonic waveguiding structures. Recent prediction of strong third-order optical response of metals due to ponderomotive forces opens up novel possibilities for utilizing this effect in the design of active plasmonic devices. We discuss the possibility of implementation of nonlinear response of metals in the design of plasmonic coupler. We analyze the structure and dispersions of linear and nonlinear guided plasmonic modes of two coupled thin metallic films and predict bifurcations of symmetry breaking.     

Plasmonic light scattering from nanoscopic metal tips

Linear light scattering by individual nanoscopic metal wire tips is investigated. Using evanescent-wave excitation, the spectral and polarization dependence of the emission are addressed. Choosing gold and tungsten as representative tip materials, intense scattering and a strongly plasmon-resonant behavior observed for gold contrasts a comparatively weak and spectrally flat response for tungsten. Spectral dependence and local-field enhancement are found to be sensitive to details of the structural parameters and can be described by a simple model. The results provide selection criteria for tips to be used in scattering-type near-field microscopy or photoemission in inelastic tunneling spectroscopy.This revised version was published online in April 2005. The last name of the corresponding author M. B. Raschke was corrected.     

Actively-controlled polarization independent extraordinary electromagnetic transmission in one-dimensional metal gratings

We present a scheme for achieving actively-controlled polarization independent extraordinary electromagnetic transmission in one-dimensional subwavelength metal gratings. The key of this realization is to introduce high refractive index and magnetic activity into the metal grating, in which the transverse electric polarized radiation can also be transmitted and the transmission peaks can be actively tuned by applied magnetic field. The single mode theory and full wave electromagnetic simulation are used to confirm our idea.     

金属微结构纳米线中等离激元传播和分光特性

本文从理论和实验两方面探讨了具有微结构的金属纳米线系统中表面等离激元传播规律和分光特性. 我们由麦克斯韦方程组出发, 利用严格耦合波近似和有限元差分等方法首先从理论上给出了金属纳米线系统中等离激元的色散关系和能带特征, 然后基于微结构的银纳米线及其等离激元能带结构, 设计并制备出等离激元分光原型器件, 实验展示其将不同频率的光在微小空间分离的特性. 该研究结果是我们前期相关工作的延续和补充, 可应用于构造多功能集成的光子芯片和新型亚波长光电材料和器件.     

Plasmonic effects in composite metal nanostructures for sensing applications

We have investigated numerically the plasmonic effect on a two-dimensional periodic array of metallic nanostructures. The unit cell of the array has an Ag nanosphere and nanorod pair formed in a single structure. Three-dimensional finite element method is used for the study on the sensing performance within the optical spectra. The study takes into account the influences of the structural and material parameters, the rotational angle of the metal nanostructure, the number of metal nanostructure per unit cell, and the localized surface plasmon resonances. The proposed nanostructures function as a refractive index sensor with a sensitivity of 400 nm/RIU (RIU is the refractive index unit), showing the characteristics of low transmittance (T?=?3.90%), high absorptance (A?=?94.5%), and near-zero reflectance (R?=?0.15%), could be achieved by a triangular arrangement of nanostructures within a unit cell. We also show how the tailoring of the structural parameters relates to the specific sensing schematics of the sensor.

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Graphical abstract x-y sectional plane of electric field intensity, electric force lines (pink lines), energy flows (green arrows) and surface charge density of type 2, corresponding to the surrounding testing medium of (a) n=1.00 and (b) n=1.33 around the PMNSs.

     

Comparison of the sensitivity of extraordinary transmittance peaks with the surrounding media for hole and slit arrays

In this paper we compare the sensitivity of the Extraordinary Transmittance (ET) peak position with the surrounding media for two types of metallic structures: arrays of holes and arrays of slits recorded in Au films. Both types of array were fabricated using Interference Lithography (IL) with a period of 700 nm and an Au thickness of 150 nm. The transmission spectra measurements were performed at normal incidence using a spectrophotometer. The results show that an array of slits presents a higher sensitivity for the surrounding media than the array of holes. Theoretical TE and TM simulations of the transmission spectra for the slit arrays agree very well with the experimental results, confirming the better sensitivity of the slit arrays.     

High-resolution surface plasmon resonance sensor based on linewidth-optimized nanohole array transmittance

A high spectral resolution, 2D nanohole-array-based surface plasmon resonance sensor that operates at normal or near normal incidence--facilitating high spatial resolution imaging--is presented. The angular and spectral transmittance of the structure is modified from a Fano type to a pure Lorentzian line shape with a parallel and orthogonal polarizer-analyzer pair. This change leads to a linewidth narrowing that maximizes the sensor resolution, which we show to be of O(10(-5)) refractive index units (RIU). We estimate the potential of this system of O(10(-6)) RIU under optimal conditions.     

Trapped electromagnetic modes and scaling in the transmittance of perforated metal films

We describe measurements and simulations of the enhanced transmittance by subwavelength hole arrays in silver films. The array period and hole size are systematically varied to give peak transmittances at wavelengths spanning a factor of 14. The spectra coincide when scaled using the array geometry and substrate refractive index alone, thus showing no significant dependence on the dielectric function of the metal. We argue that the spectra can be explained by interference of diffractive and resonant scattering. The resonant contribution comes from electromagnetic modes trapped in the film vicinity.     

Size dependence of the transmittance for metal nanofilms in the infrared region

The transmission of infrared electromagnetic waves through quasi-homogeneous thin metal films is investigated within the diagonal response approximation. An expression for the dielectric function is derived in the framework of the finite-depth potential well model with due regard for the size dependence of the Fermi energy. The transmittance of the films is calculated, and the results of the calculations are compared with experimental data. The calculations are performed for Al, Au, and Ag.     

Effects of interplay between metal subwavelength slits on extraordinary optical transmission

In this paper we study the extraordinary optical transmission of one-dimensional multi-slits in an ideal metal film.The transmissivity is calculated as a function of various structural parameters.The transmissivity oscillates,with the period being just the light wavelength,as a function of the spacing between slits.As the number of slits increases,the transmissivity varies in one of three ways.It can increase,attenuate,or remain basically unchanged,depending on the spacing between slits.Each way is in an oscillatory manner.The slit interaction responsible for the oscillating transmission strength that depends on slit spacing is the subject of more detailed investigation.The interaction most intuitively manifests as a current distribution in the metal surface between slits.We find that this current is attenuated in an oscillating fashion from the slit corners to the center of the region between two adjacent slits,and we present a mathematical expression for its waveform.     

Plasmonic electro-optic modulator design using a resonant metal grating

A plasmonic electro-optic modulator design using an evanescently coupled resonant metal grating is numerically studied in this Letter. Owing to excitation and propagation of long-range surface plasmons between the metal grating nanowires, a deep and narrow reflection dip can be obtained. Improved modulation performance is achieved through decreased damping from large dielectric gaps between the grating nanowires. An optimized electro-optic modulator design with lower insertion loss and low operating voltage is presented.     

Area-selectively sputtering the RuO2 nanorods array

The RuO₂ nanorods array is grown selectively on the SiO₂-patterned sapphire (SA) wafers using reactive sputtering. The area-selectivity is attributed to an early nucleation of RuO₂ and its fast surface coverage on SA (1 0 0) and (0 1 2), in contrast to the sluggish nucleation on glassy SiO₂ in the initial sputtering period. The growth domain is explored by investigating the temperature windows at sputtering power 40, 50, and 60 W. The low-temperature bound is limited by the mobility of precursors on SiO₂ surface, which enables the precursors to depart before aggregating into a large size to smear the non-growth region. The high-temperature bound is set by the horizontal growth which enlarges the rod width and deteriorates its one-dimensional feature. The temperature window shrinks with increasing sputtering power. The X-ray photoelectron spectra indicate the as-sputtered rod surface is ruthenium rich. The X-ray diffraction analysis shows that RuO₂ growth on SA (1 0 0) and (0 1 2) follows the epitaxial relations between RuO₂ and SA crystals.     

Control of extraordinary light transmission through perforated metal films using liquid crystals

We calculate the effective dielectric tensor of a metal film penetrated by cylindrical holes filled with a nematic liquid crystal (NLC). We assume that the director of the NLC is parallel to the film, and that its direction within the plane can be controlled by a static magnetic field, via the Freedericksz effect. To calculate the effective dielectric tensor, we consider both randomly distributed holes (using a Maxwell-Garnett approximation) and a square lattice of holes (using a Fourier technique). Both the holes and the lattice constant of the square lattice are assumed small compared to the wavelength. The films are found to exhibit extraordinary light transmission at special frequencies related to the surface plasmon resonances of the composite film. Furthermore, the frequencies of peak transmission are found to be substantially split when the dielectric in the holes is anisotropic. For typical NLC parameters, the splitting is of order 5–10% of the metal plasma frequency. Thus, the extraordinary transmission can be controlled by a static magnetic or electric field whose direction can be rotated to orient the director of the NLC. Finally, as a practical means of producing the NLC-filled holes, we consider the case where the entire perforated metal film is dipped into a pool of NLC, so that all the holes are filled with the NLC, and there are also homogeneous slabs of NLC on both sides of the film. The transmission in this geometry is shown to have similar characteristics to that in which the NLC-filled screen is placed in air.     

Plasmonic band gaps and trapped plasmons on nanostructured metal surfaces

Nanostructured metal surfaces comprised of periodically arranged spherical voids are grown by electrochemical deposition through a self-assembled template. Detailed measurements of the angle- and orientation-dependent reflectivity reveal the spectral dispersion, from which we identify the presence of both delocalized Bragg and localized Mie plasmons. These couple strongly producing bonding and antibonding mixed plasmons with anomalous dispersion properties. Appropriate plasmon engineering of the void morphology selects the plasmon spatial and spectral positions, allowing these plasmonic crystal films to be optimized for a wide range of sensing applications.     

Plasmonic nanolithography based on cavity resonance through thick metal mask

Plasmonic lithography is a very promising fabrication technology to obtain nanoscale structures beyond the diffraction limit. In this paper, a new plasmonic lithography is proposed to realize high efficiency fabrication of arbitrary patterns, which is based on cavity resonance through a thick metal mask. The mechanism of the cavity resonance transmission is explored. The one dimension (1D) and two dimension (2D) printings are simulated and discussed. The simulated results show the method that provides potential to pattern feature size with at least 40 nm, about λ/11.     

Plasmonic interactions between a metallic nanotube array and a thin metallic film

Using the finite difference time domain (FDTD) method, we numerically simulate the plasmonic interactions and the optical properties of a metallic nanotube array near a thin metallic film. We show that the energies and intensities of the plasmon resonances depend strongly on the aspect ratio (the ratio of the inner to outer radius) of the nanotube, the separation between the center of the nanotube and the upper surface of the metallic film and the thickness of the film. In the thin film limit, the high-energy localized tube-related plasmons can induce their images on both sides of the metallic film, so the degeneracy state splits into two modes. Based on the nature of the field distribution, we also show clearly the plasmon resonant characteristics that the electromagnetic fields decay away from the surface of the nanotubes and both sides of the metallic film.