Grating-coupled surface plasmon polaritons and waveguide modes in a silver-dielectric-silver structure

A silver-dielectric-silver structure that supports both waveguide modes and surface plasmon polaritons is explored. The upper interface between the dielectric and the silver is periodically corrugated to allow coupling of visible photons to both types of mode. Such a metallic microcavity leads to plasmonic and waveguide self-interacting bandgaps at Brillouin zone boundaries. In addition there are found other bandgaps from mode crossings within the Brillouin zone. This results specifically in a very flat photonic band due to anticrossings between a surface plasmon polariton and waveguide modes. Characterization of the observed modes in terms of their resonant electromagnetic fields is achieved by using a multilayer, multishape differential grating theory.     

Coupling effciency of surface plasmon polaritons to radiation using a corrugated surface; angular dependence

The paper reports measurements on the effciency of coupling between a surface plasmon polariton mode and radiation using a periodic corrugated surface. For surface plasmon polaritons (SPPs) propagating parallel to the Bragg vector of the corrugation, coupling effciencies of 70% were observed. The coupling effciency was also measured for different SPP propagation directions relative to the corrugation and found to be high over a wide range of SPP propagation directions. These results are discussed in the context of emission from SPP-based light emitting devices.     

Transmission characteristics of surface plasmon polaritons through a metallic rectangle above a metallic film

The effects of a silver rectangle on the transmission characteristics of surface plasmon polaritons (SPPs) that propagate at the air–silver interface are investigated using the finite-element method. Results show that the structural parameters of the rectangle and distance between rectangle and film significantly influence SPP-transmission characteristics. These effects are due to the restriction of SPPs at the air–silver interface and resonance around the rectangle.     

Resonant coupling between bulk waves and guided modes in a dielectric slab with a thick holographic grating

What we believe to be a new type of resonant coupling of an incident bulk wave into guided modes of a slab with a thick holographic grating is shown to occur in the presence of strong frequency detunings of the Bragg condition. This happens through the reflection of the strongly noneigen +1 diffracted order with the slab-grating boundaries, the resultant reflected waves forming a guided slab mode. Rigorous coupled-wave analysis is used for the numerical analysis of the predicted resonant effects. Possible applications include enhanced options for the design of multiplexing and demultiplexing systems, optical signal-processing devices, optical sensors, and measurement techniques.     

Effect of resonant localized plasmon coupling on the sensitivity enhancement of nanowire-based surface plasmon resonance biosensors

A nanowire-based surface plasmon resonance (SPR) is investigated as a structure that offers improved sensor performance. The results calculated by rigorous coupled-wave analysis on a model using a hexanedithiol self-assembled monolayer (SAM) indicate that the resonant coupling between localized surface plasmons (LSPs) of nanowires affects the sensitivity enhancement substantially, while the LSP resonance in a single nanowire also contributes. SPR characteristics change significantly by applying a SAM, which can give rise to zero sensitivity for a given SAM. The results suggest that a properly designed nanowire-based SPR biosensor can enhance sensitivity by an order of magnitude with reasonable detection properties.     

Semiclassical theory to optical resonant modes of a transparent dielectric spheroidal cavity

We study the resonant scattering of light by a transparent dielectric spheroid. We try to understand the features of the resonant modes of a spheroidal optical cavity. In this way, we use an analogy between optics and quantum mechanics. Through this analogy it is possible to interpret resonances as quasibound states of light. Using semiclassical methods such as the WKB method and a uniform asymptotic expansion for spheroidal radial functions, we developed algorithms that permit us to calculate the resonance position as well as the resonance width.     

Amplified spontaneous emission of surface plasmon polaritons with unusual angle-dependent response

Loss issues are fundamentally crucial for the application of surface plasmon polaritons (SPPs). In this study the amplified spontaneous emission (ASE) of SPPs in a typical Kretschmann configuration is observed and shows an unusually broadened angular response with increased pump intensity. Theoretical models are further developed to verify the results and understand the amplification of SPPs in Fourier space.     

In situ generation of surface plasmon polaritons using a near-infrared laser diode

We demonstrate a semiconductor laser-based approach which enables plasmonic active devices in the telecom wavelength range. We show that optimized laser structures based on tensile-strained InGaAlAs quantum wells-coupled to integrated metallic patternings-enable surface plasmon generation in an electrically driven compact device. Experimental evidence of surface plasmon generation is obtained with the slit-doublet experiment in the near-field, using near-field scanning optical microscopy measurements.     

All-plasmonic modulation via stimulated emission of copropagating surface plasmon polaritons on a substrate with gain

We experimentally demonstrate suppressed absorption and stimulated emission of surface plasmon polaritons (SPP) leading to all-plasmonic modulation of an SPP signal propagating at the interface between a metal and a gain medium; these observations are supported by the developed theory. The use of copropagating signal and control waves can provide more than 10 times more efficient SPP stimulated emission compared to out-of-plane pumping and opens up the possibility to realize integratable plasmonic components for active nanophotonic circuitry.     

Fabrication of surface metal nanoparticles and their induced surface plasmon coupling with subsurface InGaN/GaN quantum wells

Based on the fabrication of Ag nanoparticles (NPs) with controlled geometry and surface density on an InGaN/GaN quantum well (QW) epitaxial structure, which contains indium-rich nano-clusters for producing localized states and free-carrier (delocalized) states in the QWs, and the characterization of their localized surface plasmon (LSP) coupling behavior with the carriers in the QWs, the interplay behavior of LSP coupling with carrier delocalization in the QWs is demonstrated. By using the polystyrene nanosphere lithography technique with an appropriate nanosphere size and adjusting the post-fabrication thermal annealing condition, the induced LSP resonance wavelength of the fabricated Ag NPs on the QW sample can match the QW emission wavelength for generating the coherent coupling between the carriers in the QWs and the induced LSP. The coupling leads to the enhancement of radiative recombination rate in the QWs and results in increased photoluminescence (PL) intensity, red-shifted PL spectrum, reduced PL decay time, and enhanced internal quantum efficiency. It is found that the observed effects are mainly due to the LSP coupling with the delocalized carriers in the QWs.     

Intra-particle coupling and plasmon tuning of multilayer Au/dielectric/Au nanocrescents adhered to a dielectric cylinder

A 3D numerical study on surface plasmon resonance is presented for a multilayer Au/dielectric/Au nanocrescent structure adhered to a dielectric cylinder. Investigations are carried out on the structure’s coupling modes, local field enhancement (LFE) and plasmon tuning capability. The cavity coupling via the cylinder is found to be dominant in tuning the plasmon wavelength. This provides the possibility of tailoring the device's plasmon band by adjusting the cylinder’s size and material. By using a cylinder with higher permittivity, the plasmon peak significantly shifts to the near- or mid-infrared regime without increasing the size of the crescents, thus increase of radiation loss can be fully avoided. Extra crescent layers can also be added to the structure to induce intra-particle couplings among Au crescents and enlarge the areas of the hot-spots, without shifting the plasmon band. The LFE of the multiple-layer structure is shown to be dramatically increased through the intra-particle coupling among the Au crescents, compared with a single layer Au nanocrescent structure. Further increase of LFE can be achieved by substituting semiconductors for the dielectrics in the structure due to the charge transport at metal-semiconductor interfaces.     

Splitting and unidirectional excitation of surface plasmon polaritons by two uniform metallic nanoslits with a nanocavity antenna

A tunable splitter and source of surface plasmon polaritons (SPPs) is proposed. The structure is composed of two Ag films, with two uniform nanoslits fabricated in the lower Ag film and lying above is a movable Ag film. By changing the horizontal position of the top Ag film, the splitting ratio of the SPPs varies periodically based on SPP interference. The field distribution of the structure is investigated by using the finite-difference time-domain (FDTD) method. The period obtained by the FDTD agrees well with the Fabry–Pérot cavity model. When the SPP splitting ratio is large (or small), our structure acts as a low noise SPP source. Compared with other SPP sources, our model possesses better directionality.     

Role of surface profiles in surface plasmon-polariton-mediated emission of light through a thin metal film

We show that the emission of light mediated by surface plasmon-polaritons through a thin metal film depends sensitively on the profile of the grating structure used to couple the surface plasmon-polariton modes to light. In particular, we show that when the emission of light takes place through a metal film, a non-conformal geometry for the two surfaces of the metal film is to be preferred. Our results may be important in the design of devices such as organic light-emitting diodes.     

The surface mode of a dielectric waveguide with metal substrate

The conditions of excitation and the waveguide characteristics are determined in an analytical form for the TM₀ mode of a planar waveguide with metal substrate. This mode has a surface character, in contrast to other (bulk) modes excited in the system. The propagation and damping constants and the energy flux density distributions are compared for the TM₀ and TE₀ modes.     

Periodical concentration of surface plasmon polaritons by wave interference in metallic film with nanocavity array

Metallic thin films with nanocavity arrays provide ideal platforms for plasmonics, non-linear optics, surface chemistry and corresponding applications. A general understanding of electromagnetic (EM) field distributions is needed for further creation, manipulation and designation of near-field enhancements. Herein, we study the distribution of plasmonic hot spots over Ag thin films with triangular nanocavities in hexagonal arrays with a variable of lattice parameters. We propose that the concentration and interference of surface plasmon polaritons (SPP) dominates the distribution of plasmonic hot spots. The localized surface plasmonic resonance (LSPR) at nanocavities excites SPPs to propagate on the thin film, whose concentration and interference lead to an extremely strong near-field enhancement at the surface of the thin film, the location of which can also be termed as plasmonic hot spot. For this model, the calculation results of the physical formula are in excellent agreements with both the experimental results and the electrodynamic simulations with 3D finite element method (FEM). Moreover, the plasmonic hot spots distribute periodically within the nanocavity arrays, determined by the geometric symmetry of the array as well as with the polarization state of the incident field. The periodicity of plasmonic hot spots on flat surface illustrates a new way to concentrate SPPs in an extendable area, which has potential applications in localized non-linear optics, sensing, plasmonic logical circuit and optical computing.     

Comparative study of coupling to symmetric and antisymmetric cladding modes in long-period fiber gratings

We analyse the influence of coupling to symmetric and antisymmetric cladding modes in arc-induced Long-Period Fiber Gratings for temperature and strain sensing. The origin of this difference in energy coupling is related to the fabrication process of these gratings and depends on the electric arc discharge conditions, which modulates the refractive index and geometry of the optical fiber. Finally, results demonstrate the performance of different cladding modes excited in arc-induced LPFGs to temperature and strain applications and, in addition, indicate which coupling might be appropriate to certain sensing applications.     

Coupling of surface-plasmon polaritons to directional far-field radiation by an individual surface protrusion

An experimental study of surface-plasmon polariton scattering by an individual surface protrusion on a silver film has been performed. Both in- and out-of-plane scattering have been investigated by imaging with a photon-scanning tunneling microscope at various probe-to-sample distances. For imaging in close proximity we observed a bright spot with rims on the shadow side, but, for imaging at larger distances, the location of the bright spot shifts away from the direction of the incoming surface-plasmon polariton. We estimate a pronounced peak in the far-field scattering pattern at an angle of ~20 degrees from the sample plane, which is in good agreement with recent theoretical studies and indicates that the same protrusion could possibly be used for local launching of surface-plasmon polaritons in a reversed illumination configuration.     

Ion beam surface nanostructuring of noble metal films with localized surface plasmon excitation

Noble metal nanoparticles strongly adhered to dielectric matrices have been extensively studied because of their potential applications in plasmonic devices based on tunable localized surface plasmon (LSP) excitation. Compared with conventional synthesis methods, the noble metal nanoparticles formed by ion-beam irradiation draw significant interest in recent years because a single layer dispersion of nanoparticles strongly bonded on the dielectric substrate can be obtained. In this paper, important phenomena related to ion-beam surface nanostructuring including ion-induced reshaping of metal nanoparticles, ion-induced core-satellite structure formation, and ion-induced burrowing of these nanoparticles are discussed, with their individual effects on LSP excitation. Consequently, ion-induced surface nanostructuring of Ag-Au bimetallic films on amorphous silica glass and sapphire with tunable LSP excitation are presented. In addition, theoretical studies of far-field and near-field optical properties of these nanoparticles under ion irradiation are introduced, and the enhanced localized electric field (hot spot) is interpreted. Finally, the futures and challenges of the emerging plasmonic applications based on tunable LSP excitations in bio-sensing and surface enhanced Raman spectroscopy (SERS) are presented.