Multiple Surface Plasmon Resonances in Compound Structure with Metallic Nanoparticle and Nanohole Arrays

The optical properties of a compound structure with metallic nanoparticle and nanohole arrays are numerically investigated by the means of finite-difference time domain method. We report on the observation of multi-valleys in the reflection spectra due to the excitation of surface plasmon (SP) resonant modes of the compound structure. Simulation results show that multiple SP resonances consist of surface plasmon polaritons on the gold film, localized surface plasmons on the nanoparticles, and coupling mode between them. These findings are important for applications utilizing multiple surface plasmon resonances.     

Tunable Multi-Port Surface Plasmon Polariton Excitation with Nanostructures

Surface plasmon polaritons (SPPs) have appealing features such as tighter spatial confinement and higher local field intensity. Manipulation of surface plasmon polaritons on metal/dielectric interface is an important aspect in the achievement of integrated plasmonic circuit beyond the diffraction limit. Here, we introduce a design of pin cushion structure and a holographic groove pattern structure for tunable multi-port SPPs excitation and focusing. Free space light is coupled into SPPs through momentum matching conditions. Both nanostructures are capable of tunably controlling of SPPs depending on the incident polarizations, while the holographic method provides more flexibility of wavelength-dependent excitations. Furthermore, a quantitative method is applied to calculate the efficiencies of excitation for both nanostructures under different conditions, including radially polarized incident beams. These results can work as a guidance and be helpful to further choice of the suitable design strategies for variable plasmonic applications such as beam splitter, on-chip spectroscopy, and plasmonic detectors.     

Optimization of Optoelectronic Plasmonic Structures

We discuss the interplay between surface plasmon polaritons (SPPs) and localized shape resonances (LSRs) in a plasmonic structure working as a photo-coupler for a GaAs quantum well photodetector. For a targeted electronic inter-subband transition inside the quantum well, maximum photon absorption is found by compromising two effects: the mode overlapping with incident light and the lifetime of the resonant photons. Under the optimal conditions, the LSR mediates the coupling between the incident light and plasmonic structure while the SPP provides long-lived resonance which is limited ultimately by metal loss. The present work provides insight to the design of plasmonic photo-couplers in semiconductor optoelectronic applications.     

Excitation and Optimization Modeling of Surface Plasmon Polaritons in a Concentric Circular Metallic Grating Film

Interaction behavior between surface plasmon polaritons (SPPs) and Hankel-distributed diffracted waves (DWs) on a silver concentric circular grating film is studied using a rigorous coupled-wave technique for circular structure. It is shown that the numerical technique reveals the excitation characteristics of SPPs in the circular metal grating as well as provides an accurate calculation of SPP intensities for further optimization designs. Results show that the SPPs can be excited by various DWs through the control of wavelength and angle of the incident light. The most efficient excitation of SPPs from this circular metal grating structure can be obtained from the +1^st-order DW under a normal incidence with wavelength close to the grating period, and the optimal thickness and duty cycle of the grating are found to be 370 and 0.5 nm, respectively. It is shown that the optimized intensity of SPPs excited from circular metal grating can be higher than that from strip metal grating by over one order of magnitude.     

Design Method for Light Absorption Enhancement in Ultra-Thin Film Organic Solar Cells with the Metallic Nanoparticles

In this paper, a method is presented for designing the parameters of metallic nanoparticles introduced into ultra-thin film organic solar cells (OSCs) to improve the light absorption. On the basis of Mie theory, a relationship is setup between the scattering efficiency of localized surface plasmon resonance and the size parameter of metallic nanoparticles, by which metallic nanoparticles with optimal size can be designed to realize the highest ratio of resonant scattering to resonant absorption, thus light absorption enhancement of OSCs is maximized. By taking spherical Ag nanoparticles into an OSC system with an active layer of poly(3-hexylthiophene) and [6, 6]-phenyl-C61-butyric acid methyl ester as subject, light absorption increase of 26 % at an average wavelength of incident light is demonstrated. This design method is also applicable to other types of OSCs.     

Characteristics of Plasmonic at a Metal/Chiral Sculptured Thin Film Interface

The propagation of surface plasmon polariton at an interface of metallic thin film and chiral sculptured thin film theoretically has been investigated using the transfer matrix method in the Kretschman configuration. The optical absorption of structure as a function of polar incident angle for linear polarization P and S has been calculated at different structural parameters. The results show that exist multiple plasmon peaks for P polarization, while there are the weak plasmon peaks when incident of light is S-polarized plane wave.     

Tailoring Absorption in Metal Gratings with Resonant Ultrathin Bridges

We present a theoretical analysis of the effects of short range surface plasmon polariton excitation on subwavelength bridges in metal gratings. We show that localized resonances in thin metal bridges placed within the slit of a free-standing silver grating dramatically modify transmission spectra and boost absorption regardless of the periodicity of the grating. Additionally, the interference of multiple localized resonances makes it possible to tailor the absorption properties of ultrathin gratings, regardless of the apertures’ geometrical size. This tunable, narrow band, enhanced–absorption mechanism triggered by resonant, short-range surface plasmon polaritons may also enhance nonlinear optical processes like harmonic generation, in view of the large third-order susceptibility of metals.     

Enhanced Optical Transmission Through Metallic Holes Array: Role of TE Polarization in SPP Excitation

Optical transmission through double-layer metallic subwavelength holes array is studied under oblique incidence by split-field finite-difference time-domain method. Both TM and TE polarizations are investigated. It is proved that the transmission peaks can also be observed for TE polarization due to the excitation of surface plasmon polaritons (SPP) through diffraction orders. By changing the incident angle, these transmission peaks follow the SPP wavelength shift. The field profiles, even for the field components not present in the incident field, clearly show the SPP excitation. The mechanism of enhanced transmission will be fully discussed.     

Propagation Loss of Long-Range Surface Plasmon Polariton Gold Stripe Waveguides in the Thin-Film Limit

Propagation loss experienced by long-range plasmon polaritons in ultrathin gold stripe waveguides embedded in different polymer cladding materials was studied and correlated with atomic-scale characterization of the gold film structure. We identify the main sources of experimentally observed propagation loss which deviates from ideal values in the thin-film limit. Increased loss can be translated to an increased effective thickness of the ultrathin films due to incomplete surface coverage and the presence of diffuse interfaces, both of which depend significantly on the choice of cladding material. The results illustrate the importance of atomic-scale dynamics of metal film formation for the selection of optimum substrate materials for surface plasmon polariton waveguides, resonant transmission structures, and semitransparent electrical contacts.     

Nonlinear Nanowire Close to a Truncated Metallic Film: a Step Toward Nanosized Light Sources

A controllable nanosized light source based on nonlinear interaction of light and a semiconductor nanowire is proposed. Surface plasmon polariton (SPP) waves with different frequencies propagate along the upper and lower surfaces of a truncated metallic film and are scattered at its end face. A nanowire, in that vicinity, is pumped by the scattered light, and new harmonics are generated via second-order nonlinear optical effects. Green's function surface integral equation method is exploited to numerically calculate the electric field, the magnetic field, and the power of the generated frequency components. Results show that the power of the generated harmonics depends on the position and radius of the nanowire, thickness of the metallic film, as well as the wavelength of the incident SPP waves. On the other hand, by controlling the phase difference between incident SPP waves having the same frequencies, it is possible to manipulate the electric field pattern and also to change the power of the generated harmonics.     

Analytical Approach to the Prism Coupling Problem in the Kretschmann Configuration

Prism coupling in the Kretschmann configuration is a well-known method for excitation of surface plasmon polaritons (SPP’s) in a metal film bounded from one side by a prism and from the other side by air. The analysis of the reflectance in the upper medium (prism) is based on the well-known Fresnel’s formula. Due to the fact that this formula cannot be inverted directly to give the complex dielectric permittivity and the thickness of the metal film from measured values of the reflectance at three or more different angles of incidence, an additional analysis is needed. Here, such an analysis is presented. The special case of illumination with He–Ne laser (λ = 632.8 nm) of silver film bounded by air is considered. A new asymptotic formula for the Lorentz dip is derived. Our experimental data for silver film are reported too.     

Surface Plasmon Polariton Propagation at the Interface of a Metal and an Ambichiral Nanostructured Medium

The propagation of a surface plasmon polariton wave at the interface of a metal and an ambichiral nanostructured medium was theoretically investigated in the Kretschmann configuration using transfer matrix method. The dependence of optical absorption linear polarization on structural parameters was reported. The results were compared with those obtained from the interface of a metal and a chiral dielectric medium as a reference structure. We found that multiple plasmon modes are excited at the interface of metal and ambichiral dielectric medium. Our calculations revealed that there exist five plasmon modes for chiral, trigonal, and tetragonal structures; three plasmon modes for pentagonal structure; two plasmon modes for hexagonal structure; and one plasmon mode for dodecagonal structure that propagate with different phase speeds. The obtained results showed that only one plasmon mode occurs at all pitches, while other modes exist at some of the pitches of anisotropic chiral and ambichiral dielectric mediums. The time-averaged Poynting vector versus the thickness of metal film confirmed that the energy of photons of incident light is transferred to surface plasmon polariton quasiparticles and the surface plasmon polariton wave is localized at the interface of metal and ambichiral dielectric medium.     

Plasmon Hybridization in Silver Nanoislands as Semishells Arrays Coupled to a Thin Metallic Film

We obtained experimentally strong plasmon interactions between localized surface plasmon with delocalized surface plasmon polaritons in a new nanosystem of silver semishells island film arrays arranged as a closed-packing structure coupled to an adjacent thin silver film. We show that plasmon interactions for such a nanosystem exhibits two pronounced resonances and interpret the coupling in terms of Fano resonances. The higher energy resonance is identified as a symmetric hybridization mode between localized plasmon resonances in the island semishell array and surface plasmon polaritons in the metal film and while the lower energy resonance is identified as a corresponding anti-symmetric hybridization mode. Increasing the size of the particle arrays enhances and red shifts the resonances. We show that adding a dielectric spacer between the semishell island array and the metal film results in a red shifting of the resonances and introduce an additional high energy spectral peak. The effect of the spacer layer is interpreted as a reduced hybridization and the generation of additional localized surface plasmon resonances.     

Efficient Surface Plasmon Polariton Excitation with the Beam Generated by Micro Triangular Prism

The optical beam generated by a micro triangular prism is presented to excite surface plasmon polaritons (SPPs) on a single silver nano slit. The electromagnetic fields generated by the micro triangular prism and the excited surface plasmon polaritons are simulated with finite-difference time-domain method. Compared with directly normal incident beam, the efficiency of SPPs’ excitation with the beam generated by the micro triangular prism is highly improved.     

Using the nanoimprint-in-metal method to prepare corrugated metal structures for plasmonic biosensors through both surface plasmon resonance and index-matching effects

In this study, we prepared metallic corrugated structures for use as highly sensitive plasmonic sensors. Relying on the direct nanoimprint-in-metal method, fabrication of this metallic corrugated structure was readily achieved in a single step. The metallic corrugated structures were capable of sensing both surface plasmon resonance (SPR) wavelengths and index-matching effects. The corrugated Au films exhibited high sensitivity (ca. 800 nm/RIU), comparable with or even higher than those of other reported SPR-based sensors. Because of the unique index-matching effect, refractometric sensing could also be performed by measuring the transmission intensity of the Au/substrate SPR mode-conveniently, without a spectrometer. In the last, we demonstrated the corrugated Au film was capable of sensing biomolecules, revealing the ability of the structure to be a highly sensitive biosensor.     

Exciting Surface Plasmons with Transformation Media

We present a way of exciting surface plasmon polaritons along non-patterned metallic surfaces by means of a flat squeezing slab designed with transformation optics. The slab changes the dispersion relation of incident light, enabling evanescent coupling to propagating surface plasmons. Unlike prism couplers, the proposed device does not introduce reflections at its input interface. Moreover, its compact geometry is suitable for integration. A feasible dielectric implementation of the coupler is suggested. Finally, we show that the angular response of the device can be engineered by using a non-uniform compression factor. As an example, we design a coupler with a half-power angular bandwidth 2.5 times higher than that of a conventional dielectric coupler.     

Efficient Extraction of Fluorescence Emission Utilizing Multiple Surface Plasmon Modes from Gold Wire Gratings

We demonstrate directional enhanced fluorescence emission from fluorophores located above gold wire gratings. In contrast to previous studies on corrugated films, efficient coupling was recorded for multiple plasmon modes associated with both the active and substrate side of the wires. This difference is likely due to the subtle differences in how light interacts with corrugated films versus metal films with periodic subwavelength slots. For corrugated films, coupling between modes on opposite sides of the grating are out of phase, and therefore plasmon modes on the opposite side of the grating are only weakly excited. For wire gratings, transmission and reflection features have been modeled well with a dynamical diffraction model that includes surface plasmons, which allows for efficient coupling to surface plasmon modes on both sides of the grating. We also compared the two mechanisms for fluorescent enhancement, namely the intense electromagnetic field associated with surface plasmons and excited fluorophores radiating via surface plasmon modes. We found the latter mechanism clearly dominant.     

Optical Bifacial Transmission by Asymmetric Charge-Oscillation-Induced Light Transmission Through a Plasmonic Structure

From first-principles computation, we reveal that optical bifacial transmission can be induced within an asymmetric metallic subwavelength structure. This phenomenon can be explained by a concrete picture in which the intensity of the driving forces for surface plasmon or charge wave is asymmetric for the two incident directions. Two distinguished different numerical methods, finite difference time domain (FDTD), and rigorous coupled wave analysis (RCWA) are utilized to verify that optical bifacial transmission can exist for linear plasmonic metamaterial. Previous results are also reviewed to confirm the physical meaning of optical bifacial transmission for a planar linear metamaterial. The incident light can provide direct driving forces for surface plasmon in one direction. While in the opposite direction, forces provided by the light diffraction are quite feeble. With the asymmetric driving forces, the excitation, propagation, and light-charge conversion of surface plasmon give the rise of bifacial charge-oscillation-induced transmission. In periodic a structure, the excitation of surface plasmon polariton can lead to the spoof vanish of such phenomenon. The transmissions for two incident directions get the same in macroscopic while the bifacial still exists in microscale.     

Tunneling Intensity Enhancement of Resonant Tunneling Effects Caused by Surface Plasmon Excitations

This study investigates whether the resonant tunneling intensity of one groove of a metal film with periodic grooves on both surfaces can be enhanced by adjusting the relative permittivity of adjacent grooves of the emitting plane. As the relative permittivity of the side grooves of the emitting plane increases, the emission intensity of the center groove first increases but eventually saturates. This property is mainly attributable to concentration of incident intensity in the center groove of the incident plane. Larger numbers of lumped grooves or larger distances between two adjacent grooves increases the intensity of light entering the system, which ultimately increases the intensity of emitted light. This enhanced emission intensity achieved by resonant tunneling effects has potential applications in future plasmonic transistor designs.     

Impact of Nonuniform Electron Density on Plasmonic Properties of Metal Nanoparticles

The interfacial nonuniformity of the electron density that occurs in metals as a result of atomic imperfections can strongly affect the plasmonic properties of metallic nanostructures. Under certain conditions, it induces the bulk plasmon resonance in the transition area and can significantly change scattering and absorption of light by metallic nanostructures in a broad frequency range. This effect is numerically demonstrated for radially nonuniform spherical silver nanoparticles and analytically investigated with respect to the resonant coupling with the dipolar surface plasmons of the metal core.