Excitation Of Surface Plasmon Waves Research Articles

Computational study of optical force on a dielectric and a plasmonic nanowire

In this paper, the optical force exerted on a dielectric and a plasmonic nanowire with a circular cross-section of sub-micrometer radius anw is numerically calculated using the Muller boundary integral equations and the Minkowski electromagnetic stress tensor. A Complex Point Source (CPS) of micrometer lateral size b is used as the incident light in the visible spectral range. Computations show that the optical force acting on the dielectric nanowire is always smaller than that on the plasmonic one under the same conditions which originates from the excitation of surface plasmon waves. Calculations also reveal that the optical force in both nanowires has an oscillatory dependence on λ but there are sharp peaks for the dielectric nanowire due to the excitation of whispering gallery modes. In the plasmonic wire, however, the force angle is positive for all of the studied wavelengths but for the dielectric wire it is negative. This means that, the optical force in the plasmonic nanowire is mainly scattering-dominated but for dielectric one it is gradient-dominated.

Excitation of surface plasmon waves with a nanoantenna: simple analytical solution and its numerical verification

In this work, we demonstrate a simple analytical approach to the problem of surface plasmon polaritons excitation with a metallic nanoantenna placed above a metal surface. The method uses the reciprocity theorem and is similar to the calculation of amplitudes of dielectric waveguide modes excited by a current distribution. To maximize clarity of the demonstration, we formulate the problem in a simple two-dimensional geometry. The analytical results are shown to agree well with the numerical solution obtained by finite elements in frequency domain and finite difference in time domain methods.

Interference-enhanced optical magnetism in surface high-index resonators: a pathway toward high-performance ultracompact linear and nonlinear meta-optics

Artificial magnetism in optical frequencies is one of the most intriguing phenomena associated with metamaterials. The Mie resonance of high-index resonators provides an alternative approach to achieving optical magnetism with simple structures. Given the generally moderate refractive index exhibited by available materials at optical frequencies, Mie resonances usually suffer from coupling between the multipole modes, and the corresponding response of the Mie metasurfaces can be analyzed based on the concept of “meta-optics.” Here, we show that the optical magnetism in high-index resonators can be significantly enhanced by adding a highly reflective back mirror to the system. To highlight the transformative ability of this approach for improving meta-optics in the linear and nonlinear regimes, two proof-of-concept demonstrations are presented. Theoretical modeling reveals that low-pump power ultrafast nonlinear optics can be realized in periodic Si nanodisk arrays backed with a gold film, a system supporting guided resonance modes. Moreover, based on the enhanced magnetism of individual high-index resonators, a pair of silicon cuboids is demonstrated as a magnetic antenna for directional excitation of surface plasmon waves. The interference-enhanced magnetism of high-index resonators provides a disruptive technology for enabling meta-optics comprising ultracompact, high-speed, and power-efficient photonic devices.

SPR based magnetic-field sensing in microchannelled PCF: a numerical approach

We propose a surface plasmon resonance (SPR) based magnetic field sensor using a microchannel incorporated side-polished photonic crystal fiber (PCF). A side polished PCF, when exposed to a high energy Gaussian pulse in the transverse direction, engraves a microchannel on the flat surface. The inner surface of the microchannel is assumed to be coated with indium tin oxide (ITO) and the microchannel is to be filled with magnetic fluid (MF). The refractive index (RI) of MF could be varied via application of magnetic field. The principle of the device is based on the excitation of surface plasmon wave at the ITO-MF interface and the corresponding shift in SPR peak due to the change in RI of MF. The presence of ITO helps in excitation of surface plasmon in the near infrared wavelength band. Through numerical analysis, we estimate the magnetic field sensitivity of the proposed device to be 564 pm Oe−1 (5.64 nm/mT) for weaker magnetic field with a maximum resolution of 0.177 Oe. Further, the proposed sensor can be utilized for intensity based magnetic field sensing where its sensitivity is of the order of 0.005/Oe.

A symmetrical surface plasmon resonance sensing structure excited by a stripe waveguide

A symmetrical metal–medium–metal surface plasmon resonance (SPR) structure was excited by a stripe waveguide. The wave-vector matching condition is adjusted by changing the metal-film spacing, which in turn allows a variation of the refractive-index testing range. This structure overcomes the range limitations encountered in the intensity SPR detection method using waveguides and makes the matching condition of wave vectors more flexible. A single-mode stripe waveguide was designed and fabricated to excite the symmetrical sensing structure based on a planar waveguide using the complementary error function as the refractive-index distribution. The stripe waveguide is analyzed more conveniently and is easily cured with optical fibers for remote online measurement. The coupling testing system of the optical fiber with the symmetrical structure excited by the stripe waveguide was constructed to facilitate the excitation of surface plasmon waves. The impacts of the metal type, the metal film thickness, and the medium thickness in the symmetrical structure were investigated to optimize the sensing structure. The resonance condition is achieved much more easily in the symmetrical than in the traditional structure, and the detection range is adjustable via the medium thickness. Online and adjustable measurements were realized simultaneously by the detection system.

Analysis of surface plasmon resonance based bimetal coated tapered fiber optic sensor with enhanced sensitivity through radially polarized light

The presented proposal of surface plasmon resonance (SPR) configuration with tapered fiber structure and radially polarized light beam is a new and different analysis towards the sensitivity enhancement in the field of SPR based fiber optic sensors. Here the taper waist region of optical fiber having diameter around 330μm is deposited with 40nm thin Ag layer, 10nm thin Au layer and the sensing layer with refractive index 1.333–1.353 respectively for achieving the bimetal coated taper fiber optic sensor with SPR configuration. The cylindrical symmetry and special radial field distribution of radially polarized light make its more interesting SPR study and leads to the enhanced excitation of surface plasmon wave. This results 10 times better sensitivity of fiber optic sensor output response as compared to p-polarized light beam with wavelength interrogation technique and 2.307 times better sensitivity with intensity interrogation technique. Also including the temperature effect in proposed taper bimetallic structure, this sensitivity analysis provides an evidence, for exploring a new idea towards the enhanced excitation of SPR which expedites the new avenues in the field of sensor applications with radially polarized light.

Spatial dispersion effects upon local excitation of extrinsic plasmons in a graphene micro-disk

Excitation of surface plasmon waves in extrinsic graphene is studied using a full-wave electromagnetic field solver as analysis engine. Particular emphasis is placed on the role played by spatial dispersion due to the finite size of the two-dimensional material at the micro-scale. A simple instructive set up is considered where the near field of a wire antenna is held at sub-micrometric distance from a disk-shaped graphene patch. The key-input of the simulation is the graphene conductivity tensor at terahertz frequencies, being modeled by the Boltzmann transport equation for the valence and conduction electrons at the Dirac points (where a linear wave-vector dependence of the band energies is assumed). The conductivity equation is worked out in different levels of approximations, based on the relaxation time ansatz with an additional constraint for particle number conservation. Both drift and diffusion currents are shown to significantly contribute to the spatially dispersive anisotropic features of micro-scale graphene. More generally, spatial dispersion effects are predicted to influence not only plasmon propagation free of external sources, but also typical scanning probe microscopy configurations. The paper sets the focus on plasmon excitation phenomena induced by near field probes, being a central issue for the design of optical devices and photonic circuits.

Surface plasmon excitation at near-infrared wavelengths in polymer optical fibers.

We report the first excitation of surface plasmon waves at near-infrared telecommunication wavelengths using polymer optical fibers (POFs) made of poly(methyl methacrylate) (PMMA). For this, weakly tilted fiber-Bragg gratings (TFBGs) have been photo-inscribed in the core of step-index POFs and the fiber coated with a thin gold layer. Surface plasmon resonance is excited with radially polarized modes and is spectrally observed as a singular extinction of some cladding-mode resonances in the transmitted amplitude spectrum of gold-coated TFBGs. The refractometric sensitivity can reach ∼550 nm/RIU (refractive index unit) with a figure of merit of more than 2000 and intrinsic temperature self-compensation. This kind of sensor is particularly relevant to in situ operation.

Polarization-selective optical transmission through a plasmonic metasurface.

We present the design, fabrication, and experimental characterization of a nanoslit-based metasurface that offers polarization-selective optical transmission for advanced imaging applications. The metasurface consists of an array of meta-atoms, constructed with two orthogonally coupled subwavelength apertures. Highly enhanced optical transmission was achieved by selective excitation of surface plasmon waves on the metasurface. By rotating the orientation of the linearly polarized incident beam, switching of enhanced optical transmission bands through the metasurface was experimentally demonstrated. This demonstration is a significant step towards developing advanced multispectral imaging devices.

Electromagnetically-induced-transparency plasmonics: Quantum-interference-assisted tunable surface-plasmon-polariton resonance and excitation

An experimentally feasible configuration of a prism coupler with an electromagnetically-induced-transparency (EIT) medium layer, e.g., a semiconductor-quantum-dot (SQD) medium, deposited upon its prism base is suggested for generating tunable surface-plasmon-polariton resonance. Such surface-plasmon-polariton resonance and optical excitation of a surface plasmon wave can be manipulated by switchable quantum interference among SQD multilevel transitions driven by two external control fields. When an incident probe field is coupled into a surface plasmon wave excitation mode, the surface-plasmon-polariton (SPP) resonance at the interface between the SQD medium layer and the substrate will arise, and the quantum-coherently controllable reflection spectrum of the probe field on the prism base can be achieved. In this process, destructive and constructive quantum interference (determined by the intensity ratio of the two external control fields) in the SQD multilevel system plays a key role for achieving the tunable reflection spectrum. The EIT-based surface-plasmon-polariton resonance presented here will have three characteristics (some of them would be attractive): (i) switchable quantum interference exhibited by surface plasmon wave excitation, (ii) quantum-coherently controllable surface plasmon polaritons by external optical fields, (iii) surface wave sensitive to dispersion of the SQD quantum coherent medium. Such an effect of controllable optical response based on the quantum-interference switchable surface-plasmon-polariton resonance in the EIT-prism coupler may find some potential applications in design of new photonic and quantum optical devices.

Robust multispectral transparency in continuous metal film structures via multiple near-field plasmon coupling by a finite-difference time-domain method

We propose a robust multispectral transparent plasmonic structure and calculate its transparency response by using the three-dimensional finite-difference time-domain (FDTD) method. The proposed structure is composed of a continuous ultrathin metal film sandwiched by double two-dimensional (2D) hexagonal non-close-packed metal-dielectric multilayer core-shell nanoparticle arrays. The top and bottom plasmonic arrays in such a structure, respectively, act as the light input and output couplers to carry out the efficient trapping and release of light. Near-perfect multispectral optical transparency in the visible and near-infrared regions is achieved theoretically. The calculated electric field distribution patterns show that the near-perfect multispectral optical transparency mainly originates from the excitation and hybridization of shell and core plasmon modes, strong near-field coupling of dipole plasmon modes between adjacent nanoparticles as well as the excitation of surface plasmon waves of the metal film. The robust transparency bands can be efficiently tuned in a large range by varying the structural parameters and the surrounding dielectric environment. The proposed structure also shows additional merits such as a deep sub-wavelength size and fully retained electrical and mechanical properties of the natural metal. These features might provide promising applications in highly integrated optoelectronic devices including plasmonic filters, nanoscale multiplexers, and non-linear optics.

Transmitive Spectral SPR Droplet Biosensing: Principle, Sensor Design, and Experimental Demonstration

Surface plasmons resonance (SPR) architectures based on grating coupler/disperser combination is an attractive alternative for spectral-based biochemical sensing. In this paper, we investigate theoretically and experimentally a new concept where the plasmon coupling occurs through a thin film grating and sensing occurs via the first evanescent diffraction order in transmitive mode. The surface plasmon wave excitation induces a peak in the wavelength as well as in the angular spectra of the detected first transmitted diffraction order. Accordingly, a change in SPR spectrum of the detected diffraction order can be used to quantify the amount of the target molecules immobilized on the sensor surface, and therefore, the concentration of these molecules in the analyte solution. The developed sensor architecture is dedicated to droplet biochemical sensing and appears to be especially suitable for biosensor integration and miniaturization. The presented sensor concept is perfectly suited for mass production of low-cost and reproducible SPR sensor chip for biochemical analysis. The implemented setup gives access to multichannel biosensing with the potential for efficient internal referencing essential to achieve sufficiently high reproducibility and accuracy of the measurements.

Correlation between dielectric constants and enhancement of surface plasmon resonances for thin gold films

Optical properties of thin gold films evaporated on glass substrates were studied with the method of spectroscopic ellipsometry in both external and internal reflection configurations as well as with the UV–visible absorption spectroscopy. Here, we discussed how ellipsometric functions Psi and Delta in the spectral region of excitation of surface plasmon waves are related to the dielectric functions (ratio ϵ1m/ϵ2m) of the thin gold films for different thickness and adhesive layers. The obtained results showed a gradual shift of the plasmon peak from 580 nm for 55 nm thick films to more than 700 nm for thin (15 nm) gold films. This study also reports an effective method to enhance the surface plasmon resonance (SPR) on Au films by using a thin Al seed layer assisted deposition. Experimental results show that the Au/Al films exhibit an enhanced SPR over the Au/Cr and Au/Ti films with a narrower full width at half-maximum. It was found that Al acts as a roughness-diminishing growth layer for the Au film while at the same time maintaining and enhancing the plasmonic properties of the combined structures.

Investigation of the near field distribution in circular nanostructures using Stokes polarization states

In this paper, the near field distribution patterns formed from nanostripe corral and half spiral are investigated. Various near field distribution patterns are generated owning to the interference of propagating surface plasmon waves that emerged from the nanoslits or nanostripe. The half spiral nanoslits are illuminated with Stokes polarizations. Each polarization state shows a different field pattern at different locations on the surface of metal film. This is due to the excitation of surface plasmon waves at different parts of the nanostructures when illuminated with different types of polarization states. The same Stokes polarization states are also illuminated on a nanostripe corral structure. In this case, dipolar field distributions are observed when illuminated with different linear polarization states, while optical vortices are observed for circular polarization. It is believed that these interesting field patterns due to different arrangements of nanostructures could be used for near field imaging and polarization sensing.

Near-unity transparency of a continuous metal film via cooperative effects of double plasmonic arrays

Metal structures with high optical transparency and conductivity are of great importance for practical applications in optoelectronic devices. Here we investigate the transparency response of a continuous metal film sandwiched by double plasmonic nanoparticle arrays. The upper nanoparticle array shows efficient light trapping of the incident field, acting as a light input coupler, and the lower nanoparticle array shows a light release gate opening at the other side, acting as the light output coupler. The strong near-field light–matter interactions of the nano-scale separated plasmonic nanoparticles, the excitation of surface plasmon waves of the metal film, and their cooperative coupling effects result in broadband scattering cancellation and near-unity transparency (up to 96%) in the optical regime. The transparency response in such a structure can be efficiently modified by varying the gap distance of adjacent nanoparticles, dielectric environments, and the distance between the plasmonic array and the metal film. This motif may provide a new alternative approach to obtain transparent and highly conducting metal structures with potential applications in transparent conductors, plasmonic filters, and highly integrated light input and output components.

Hybrid photonic surface-plasmon-polariton ring resonators for sensing applications

We introduce a hybrid photonic surface plasmon ring resonator which consists of a silicon nitride (Si3N4) dielectric traveling-wave ring resonator vertically coupled to a thin layer of metallic strip ring resonator made of Silver (Ag) on top. The cladding is assumed to be porous alumina on top of the metal layer, which provides more surface area for the adsorption of target molecules and their efficient interaction with the surface plasmon wave excited at the metal-cladding interface. Simulations show that this hybrid structure has a large refractive index sensitivity due to the excitation of surface plasmon waves and also a relatively narrow resonance linewidth due to the large quality factor of the photonic ring resonator. The Finite Element method is used to systematically design the hybrid structure and to investigate the performance of the hybrid resonator as a refractive index sensor. The proposed structure is very compact and can be implemented on a chip in an integrated platform. Thus, it can be used for lab-on-a-chip sensing applications and is capable of being spectrally and spatially multiplexed for muti-analyte sensing.

Plasmonic Structures Based on Subwavelength Apertures for Chemical and Biological Sensing Applications

Periodic arrays of apertures with subwavelength dimensions and submicron periodicity were fabricated on gold-coated tips of silica optical fibers using focused ion beam (FIB) milling. Interaction of light with subwavelength structures such as an array of nanoapertures in an optically thick metallic film leads to the excitation of surface plasmon waves at the interfaces of the metallic film and the surrounding media, thereby leading to a significant enhancement of light at certain wavelengths. The spectral position and magnitude of the peaks in the transmission spectra depend on the refractive index of the media surrounding metallic film containing the nanohole array. This lays the foundation for the development of fiber-optic chemical and biological sensors that sense the change in refractive index of the medium around the metallic film. This is demonstrated by testing the sensors with solutions of alcohols with different refractive indices and by the attachment of biomolecules to the sensor surface. The bulk refractive index sensitivity of these nanoaperture array-based sensors is shown to be higher than what has been typically reported for metallic nanoparticle-based plasmonic sensors.

Demagnifing super resolution imaging based on surface plasmon structures

An imaging mechanism for demagnifing features above wavelength into desired images beyond the diffraction limit is proposed in this letter. The super resolution ability (about two times and even more that of diffraction limit) arises from the surface plasmon wave excitation and amplification associated with metallic grating structure. Two specifically designed masks are projected to the grating surface from both sides, at one of which the superimposed field forms the desired images. Conceptually formalism of the imaging process is presented using spatial Fourier analysis and illustrated with numerical simulations.

A Theoretical Analysis of Backscattering Enhancement Due to Surface Plasmons From Multilayer Structures With Rough Interfaces

Backscattering enhancement is a phenomenon in rough surface scattering which manifests itself as a well defined peak in the backscattering direction. In a small roughness regime, backscattering enhancement is induced by the excitation of surface plasmon waves along a certain path followed by their retracing the same path in the reverse direction. In this paper, an accurate solution to two-dimensional scattering from multilayer rough surfaces based on extended boundary condition method and scattering matrix approach is used, which in effect incorporates all orders of scattering. The criteria for observing backscattering enhancement using this method are discussed and the wavenumbers of surface plasmon waves for a two-layer medium are derived. The proposed technique provides rigorous solutions for backscattering enhancement and satellite peaks. Numerical simulations are performed on a dielectric slab deposited on a silver film for both HH and VV polarizations and the emphasis is placed on the effects of subwavelength features of layered rough surfaces on the phenomenon of backscattering enhancement. Particular attention is given to the impact of layer thickness on backscattered enhanced peaks. Finally, the presence of satellite peaks due to the excitation of multiple surface plasmon waves in a layered structure is also demonstrated.

Differential theory of diffraction in cylindrical coordinates

AbstractThe principles of the differential theory of light diffraction are presented in cylindrical coordinates. Special attention is played to the factorisation rules necessary to obtain faster convergence with respect to the number of basic functions used in the field representation. A detailed description is given for diffracting objects having rotational symmetry and finite cylindrical length. Some properties of light diffracted by a single circular aperture piereced in a finitely conducting screen are discussed, including the excitation of surface plasmon wave and the enhanced beaming. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)