Propagation Of Surface Plasmon Polaritons Research Articles

Role of quantum-coherence dressed states on the Fresnel–Fizeau drag and optical properties of surface plasmon polaritons through asymmetric double quantum dot-metallic plasmonic interfaces

Owing to the exceptional structural-design flexibility and tunability of physical properties of quantum dots, the manipulation of light in view of surface plasmons via dots–based hybrid nanostructures and dots-metallic interfaces finds promising device applications. Hereby, we first demonstrate theoretically the role of intense laser-excited dressed states on the light propagation, optical properties, and lateral and rotary drag of surface plasmon polaritons (SPPs), via plasmon-assisted induced transparency (PIT). For this, we employed a scheme of plasmonic interface comprising an asymmetric double quantum dot molecule GaAs/AlGaAs in the Λ − type configuration embedded in gold metallic surface. In particular, using density-matrix formulation, we present a detailed analytical solution of the quantum dot system for the required eigenvalues in view of the dressed eigenstates. The dressed states played a vital role in the formation of PIT transparency and hence the manipulation of SPPs propagation, optical properties and SPPs drag, via quantum interference. The calculated theoretical results on the optical properties such as absorption and dispersion spectrum, group index, group velocity, group delay, phase delay, wave vector, propagation length and SPPs drag are further elaborated with aid of numerical simulation. The maximum calculated lateral and rotary SPPs drag was of order ± 6.0 × 10−8 m or rad, respectively. The value of SPPs propagation lengths calculated along and perpendicular to the dot-metallic interface are 3.3 × 10−7 m and 2.0 × 10−9 m, respectively.

Dispersion of resonant modes in patch antenna lattices.

Spectroscopic polar angle resolved Mueller matrix ellipsometry at multiple azimuthal incidences, together with a full-field model, reveal new details in the interplay between localized gap surface plasmon resonances and propagating surface plasmon polaritons (SPPs) in a rectangular array of metal-insulator-metal patches. A plane-wave expansion of the field in the insulator shows that the fundamental localized resonances are composed of oppositely propagating modes. Sharp dispersive resonances observed in p-polarization, excited near the opening of diffracted orders, are shown to be grating coupled SPPs. The SPPs show strong coupling with localized modes of similar symmetry, while they appear suppressed by modes of dissimilar symmetry.

THz pulse train generation through ultrafast development of surface plasmon-polariton modulation instability

Propagation of high-intensity electromagnetic waves in a waveguide structure could initiate nonlinear effects resulting in drastic changes of their spatial and temporal characteristics. We study the modulation instability effect induced by propagation of surface plasmon polaritons in a silver thin-film waveguide. The nonlinear Schrodinger equation for propagating surface plasmon wave is obtained. It is shown numerically that the modulation instability effect can give rise to ultrafast spatial redistribution and longitudinal localization of surface plasmon-polariton wave energy in subwavelength scale. The dependence of plasmon wave dispersion and nonlinear characteristics on metal film thickness is considered. We demonstrate that the use of films with the thickness varying along the waveguide length allows reduction of the generated pulse width and increase of frequency comb bandwidth. The proposed technique is promising for design of ultra-compact (tens of nm) optical generators delivering pulse trains with the repetition rate higher than 1 THz.

Coherence Between Different Propagating Surface Plasmon Polariton Modes Excited by Quantum Mechanical Tunnel Junctions

AbstractCoherence between different surface plasmon polariton (SPP) modes excited by inelastically tunneling electrons in biased metal–insulator–metal tunnel junctions (MIM‐TJs) is demonstrated. By employing a dedicated SPP stripe waveguide with MIM‐TJ, an effective double‐slit configuration similar to the Young's experiment is realized for an electrically biased SPP source. The spatial correlation between different SPP modes originates from a single inelastic tunneling event and leads to strong interference in the far‐field, observed as alternate bright and dark fringes in the Fourier plane. The measured fringe‐spacing inversely follows the stripe waveguide length, with upper limit dictated by the SPP propagation length, confirming the SPP mediated spatial correlation. Finite difference time domain simulations support the experimental findings. Also, the experimental and simulation results unambiguously demonstrate the two‐step plasmonic decay process in plasmonic MIM‐TJs. The results presented here provide a simple and robust demonstration of the inherent coherence existing between different decay channels (plasmons and photons) of the inelastically tunneling electrons and can be exploited for plasmonic applications with tailored spatial coherence with implications in plasmon amplification and quantum information processing.

Negative refraction in twisted hyperbolic metasurfaces.

Hyperbolic metasurfaces with unique dispersion properties can manipulate light-matter interactions according to the demands. However, due to their inherent physical properties, topological transitions (flat bands) exist only in the orthogonal directions, which greatly limit their application. Here, we unveil rich dispersion engineering and topological transitions in hyperbolic metasurfaces. Based on the effective medium theory, the rotation matrix is introduced into the dispersion relation to explain the distorted energy band diagrams, iso-frequency contours and higher-order multi-dipoles of the novel twisted metasurfaces, thereby forming multi-directional topological transitions and surface plasmon polariton propagation. Furthermore, we develop an integrated model to realize new dual-channel negative refraction and nondiffraction negative refraction. The phenomena observed in the experiments match well with the simulations, which proves that the designed metasurfaces make new types of negative refraction possible and will help to overcome the diffraction limit. The hyperbolic metasurfaces presented here exhibit exceptional capabilities for designing microscopes with a super lens at the molecular level, concealment of military aircraft, invisibility cloaks and other photonic devices with higher transmission efficiency.

Polarization-controlled generation and superposition of surface plasmon polariton vortices with a plasmonic metasurface

Optical vortex that carries orbital angular momentum has shown great potential in various applications, including high-density optical communication, quantum information, and manipulation of small particles. Here, an approach to design a plasmonic metasurface that can control both the generation and superposition of surface plasmon polariton (SPP) vortices is proposed and demonstrated. Under circularly polarized light incidence, the SPP vortices with different topological charges can be generated depending on the spin of the incidence, and the superposition state can be achieved when the polarization of incident light turns to linear polarization. Furthermore, it is demonstrated that the superposition of SPP vortices can be accurately controlled by the polarization states of the incidence. This proposed approach is quite versatile for generating and controlling SPP vortices and provides a feasible way to design miniaturized photonic devices for on-chip optical micromanipulation, sensing, and other related applications.

Helicity-selective Raman scattering from in-plane anisotropic α-MoO3

Hyperbolic crystals, such as α-MoO3, can support large wavevectors and photon density as compared to the commonly used dielectric crystals, which makes them a highly desirable platform for compact photonic devices. The extreme anisotropy of the dielectric constant in these crystals is intricately linked with the anisotropic character of the phonons, which along with photon confinement leads to the rich physics of phonon polaritons. However, the chiral nature of phonons in these hyperbolic crystals have not been studied in detail. In this study, we report our observations of helicity selective Raman scattering from flakes of α-MoO3. Both helicity-preserving and helicity-reversing Raman scattering are observed. Our studies reveal that helical selectivity is largely governed by the underlying crystal symmetry. This study shed light on the chiral character of the high symmetry phonons in these hyperbolic crystals. It paves the way for exploiting proposed schemes of coupling chiral phonon modes into propagating surface plasmon polaritons and realizing compact photonic circuits based on helical polarized light.

Multifunctional Plasmonic Grating Based on the Phase Modulation of Excitation Light.

Multifunctional optical devices are desirable at all times due to their features of flexibility and high efficiency. Based on the principle that the phase of excitation light can be transferred to the generated surface plasmon polaritons (SPPs), a plasmonic grating with three functions is proposed and numerically demonstrated. The Cherenkov SPPs wake or nondiffracting SPPs Bessel beam or focusing SPPs field can be correspondingly excited for the excitation light, which is modulated by a linear gradient phase or a symmetrical phase or a spherical phase, respectively. Moreover, the features of these functions such as the propagation direction of SPPs wake, the size and direction of the SPPs Bessel beam, and the position of SPPs focus can be dynamically manipulated. In consideration of the fact that no extra fabrication is required to obtain the different SPPs fields, the proposed approach can effectively reduce the cost in practical applications.

Nonlinear TMOKE enhancement in 1D Au/Py magnetoplasmonic crystals

Resonant optical properties of the magnetoplasmonic crystals, which support propagation of surface plasmon polaritons (SPPs) accompanied by magnetooptical effects, have found success in magnetic field driven control of optical radiation. In this work we investigate the resonant magnetooptical effects in the second harmonic generation in the magnetoplasmonic crystal formed by gold/pemalloy bifilm covering dielectric grating. Strong transverse magnetooptical Kerr with the contrast up to 30% is revealed in the spectral vicinity of the SPP excitation.

Transverse Anderson localization of evanescent waves propagating in randomly layered media

We study theoretically the transverse Anderson localization of light in the simplest geometry, where the p-polarized wave propagates along the layers in the randomly stratified dielectric and evanesces exponentially in the direction across the layers. In this case, there exist two reasons for the localization of the wave in the direction transverse to its propagation: the usual evanescent wave confinement and the Anderson mechanism related to the randomness of the spatial distribution of permittivity. We solve the problem using the retarded-Green-function formalism in the Born approximation and show that, for fixed values of the wave frequency ω and wavenumber q, the random inhomogeneity results in the weakening of the wave localization. In the case of the surface plasmon-polaritons (SPPs) propagation, the Anderson mechanism changes the dispersion law for SPPs, moving the dispersion curves away from the light line. Therefore, the localization depth varies in different ways when increasing the disorder, depending on which of the values, wave vector q or frequency ω, is fixed. Namely, the localization depth increases for given q, but it decreases for given ω.

Theoretical Study on Metasurfaces for Transverse Magneto-Optical Kerr Effect Enhancement of Ultra-Thin Magnetic Dielectric Films.

We study how to enhance the transverse magneto-optical Kerr effect (TMOKE) of ultra-thin magnetic dielectric films through the excitation of strong magnetic resonances on metasurface with a metal nanowire array stacked above a metal substrate with an ultra-thin magnetic dielectric film spacer. The plasmonic hybridizations between the Au nanowires and substrate result in magnetic resonances. The periodic arrangement of the Au nanowires can excite propagating surface plasmon polaritons (SPPs) on the metal surface. When the SPPs and the magnetic resonances hybridize, they can strongly couple to form two strong magnetic resonances, which are explained by a coupled oscillator model. Importantly, benefitting from the strong magnetic resonances, we can achieve a large TMOKE signal up to 26% in the ultra-thin magnetic dielectric film with a thickness of only 30 nm, which may find potential applications in nanophotonics, magnonics, and spintronics.

Fiber-optic meta-tip with multi-sensitivity resonance dips for humidity sensing

In response to the requirements of small effective sensing volume for simultaneous interpreting of resonant peaks with different sensing sensitivities, a surface plasmon resonance (SPR) fiber-optic probe based on non-uniform Au groove array is proposed, which realizes relative humidity (RH) sensing by coating silk fibroin film. The RH meta-tip is mainly composed of multi-mode fiber (MMF), a metasurface, and silk fibroin film. The metasurface is transferred to the end face of the MMF by the “contact and separate” transfer method, and then a layer of silk fibroin is coated on the metasurface by dipping method. Because of the interaction of interference and plasma excitation, the proposed SPR probe has many resonance dips with different refractive index (RI) sensitivities, which has the potential to monitor multiple sensing parameters. Because the RI of the silk fibroin film is directly affected by the external environment RH, the phase matching conditions of the propagating surface plasmon polaritons (SPPs) change accordingly, leading to the shifts in the resonance wavelength of those dips. By further improving the functional integration of the fiber-optic SPR probe, the single-ended sensor paves the way for chemical and biological sensing.

Ultra-Narrow SPP Generation from Ag Grating.

In this study, we investigate the potential of one-dimensional plasmonic grating structures to serve as a platform for, e.g., sensitive refractive index sensing. This is achieved by comparing numerical simulations to experimental results with respect to the excitation of surface plasmon polaritons (SPPs) in the mid-infrared region. The samples, silver-coated poly-silicon gratings, cover different grating depths in the range of 50 nm–375 nm. This variation of the depth, at a fixed grating geometry, allows the active tuning of the bandwidth of the SPP resonance according to the requirements of particular applications. The experimental setup employs a tunable quantum cascade laser (QCL) and allows the retrieval of angle-resolved experimental wavelength spectra to characterize the wavelength and angle dependence of the SPP resonance of the specular reflectance. The experimental results are in good agreement with the simulations. As a tendency, shallower gratings reveal narrower SPP resonances in reflection. In particular, we report on 2.9 nm full width at half maximum (FWHM) at a wavelength of 4.12 µm and a signal attenuation of . According to a numerical investigation with respect to a change of the refractive index of the dielectric above the grating structure, a spectral shift of can be expected, which translates to a figure of merit (FOM) of about 1421 . The fabrication of the suggested structures is performed on eight-inch silicon substrates, entirely accomplished within an industrial fabrication environment using standard microfabrication processes. This in turn represents a decisive step towards plasmonic sensor technologies suitable for semiconductor mass-production.

Fabrication of Bloch Long Range Surface Plasmon Waveguides Integrating Counter Electrodes and Microfluidic Channels for Multimodal Biosensing

We report the fabrication of a novel multimodal biosensor combining plasmonic and electrochemical detection. The plasmonic sensors are based on monitoring the propagation of Bloch long-range surface plasmon polaritons (LRSPPs) along thin narrow Au stripes, integrating grating couplers as input/output means. The electrochemical sensors use the same Au stripes as working electrodes with nearby Pt stripes integrated on-chip as counter electrodes. The structures are fabricated on a truncated 1D photonic crystal comprised of a 15-period stack of alternating layers of SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> . The Au and Pt stripes are fabricated using bilayer lift-off photolithography, and the gratings are fabricated using e-beam lithography. The structures are arranged into arrays targeting multichannel biosensing. The wafer is covered with CYTOP as the upper cladding with etched microfluidic channels providing access to the sensing surfaces and is wafer-bonded to a Borofloat silica wafer to encapsulate the fluidic channels and enable edge (in-plane) fluidic interfacing. The wavelength response of the grating-coupled plasmonic waveguide sensors is presented along with surface sensing results. Cyclic voltammetry measurements using the Au and Pt stripes as the working and counter electrodes are also presented. [2021-0103]

Suppressed Transmission of Long-Range Surface Plasmon Polariton by TE-Induced Edge Plasmon.

Work on controlling the propagation of surface plasmon polaritons (SPPs) through the use of external stimuli has attracted much attention due to the potential use of SPPs in nanoplasmonic integrated circuits. We report that the excitation of edge plasmon by TE-polarized light passing across gapped-SPP waveguides (G-SPPWs) leads to the suppressed transmission of long-range SPPs (LRSPPs) propagating along G-SPPWs. The induced current density by highly confined edge plasmon is numerically investigated to characterize the extended radiation length of decoupled LRSPPs by the TE-induced edge plasmon. The suppressed transmission of LRSPPs is confirmed using the measured extinction ratio of the plasmonic signals which are generated from the modulated optical signals, when compared to the extended radiation length calculated for a wide range of the input power. It is also shown that LRSPP transmission is sensitive to the excited power of edge plasmon in the gap through the permittivity change near the gap. Such a control of SPPs through the use of light could be boosted by the hybridized edge plasmon mode and a huge field enhancement using nanogap, gratings or metasurfaces, and could provide opportunities for ultrafast nano-plasmonic signal generation that is compatible with pervasive optical communication systems.

Controllable Excitation of Surface Plasmon Polaritons in Graphene‐Based Semiconductor Quantum Dot Waveguides

AbstractThe research aim of this study is the development of a theoretical semiclassical model of the controllable excitation and propagation of surface plasmon polaritons (SPPs) in planar graphene waveguides by the application of external voltage. The model is based on the numerical solution of the SPP's dispersion equation formulated for a system including two coupled graphene sheets with embedded quantum dots. Using the developed model, the different near‐field patterns realized in the waveguides depending on the quantum dots' ordering and an external voltage applied independently to each graphene sheet with additional gold electrodes are numerically investigated. The obtained results show that the application of external voltage can locally change the chemical potential of graphene and, thereby, lead to controllable excitation of SPPs in the corresponding graphene waveguide. Furthermore, we revealed that the propagation direction of the excited SPPs is determined by the geometrical configurations of the gold electrodes that provide the required SPP routing. The investigated system offers new opportunities for near‐field energy transport and concentration, which can be applied to develop ultra‐compact photonic devices.

Machine learning-based leaky momentum prediction of plasmonic random nanosubstrate.

In this work, we explore the use of machine learning for constructing the leakage radiation characteristics of the bright-field images of nanoislands from surface plasmon polariton based on the plasmonic random nanosubstrate. The leakage radiation refers to a leaky wave of surface plasmon polariton (SPP) modes through a dielectric substrate which has drawn interest due to its possibility of direct visualization and analysis of SPP propagation. A fast-learning two-layer neural network has been deployed to learn and predict the relationship between the leakage radiation characteristics and the bright-field images of nanoislands utilizing a limited number of training samples. The proposed learning framework is expected to significantly simplify the process of leaky radiation image construction without the need of sophisticated equipment. Moreover, a wide range of application extensions can be anticipated for the proposed image-to-image prediction.

Plasmonic spin-Hall effect of propagating surface plasmon polaritons in Ni80Fe20 microstructures

Photoexcitation and shaping of a propagating surface plasmon polariton (SPP) on silver and gold microstructures are well established and lead to the discovery of the plasmonic spin-Hall effect recently. Whereas silver is often the material of choice due to its exceptional low plasma frequency and weak damping, similar observations have not been reported for ferromagnetic metals. In this work, we report on propagating SPPs on Ni80Fe20 microstructures imaged by photoemission electron microscopy (PEEM) in combination with a tunable femtosecond laser system at MHz repetition rate. Circular dichroic (CD) images in threshold PEEM show clear edge-induced SPPs with sub-micrometer wavelength and propagation length of about 3.5 μm. Analysis of the interference patterns as well as the coupling of the optical spin angular momentum to the observed fringe fields reveal propagation characteristics exclusive to evanescent waves and the presence of the plasmonic spin-Hall effect. Our work provides direct evidence that many materials with a high plasma frequency allow for excitation and observation of propagating SPPs at the dielectric/metal interface via CD PEEM imaging, enabling magnetoplasmonic investigation of common ferromagnets on nanometer length and femtosecond time scales.

Pronounced Linewidth Narrowing of Vertical Metallic Split-Ring Resonators via Strong Coupling with Metal Surface.

We theoretically study the plasmonic coupling between magnetic plasmon resonances (MPRs) and propagating surface plasmon polaritons (SPPs) in a three-dimensional (3D) metamaterial consisting of vertical Au split-ring resonators (VSRRs) array on Au substrate. By placing the VSRRs directly onto the Au substrate to remove the dielectric substrates effect, the interaction between MPRs of VSRRs and the SPP mode on the Au substrate can generate an ultranarrow-band hybrid mode with full width at half maximum (FWHM) of 2.2 nm and significantly enhanced magnetic fields, compared to that of VSRRs on dielectric substrates. Owing to the strong coupling, an anti-crossing effect similar to Rabi splitting in atomic physics is also obtained. Our proposed 3D metamaterial on a metal substrate shows high sensitivity (S = 830 nm/RIU) and figure of merit (FOM = 377), which could pave way for the label-free biomedical sensing.

Propagating Surface Plasmon Polaritons Excited at the Graphene Oxide/AgAu Alloy Interface Enhance Nonlinearity

In article number 2000602 by Giuseppina Simone, to overcome the challenges posed by the synthesis of the hybrid graphene oxide (GO)/metal system, nanometric AgAu-alloy has been grown inside the network of proteinaceous micrometric cages before the immobilization on top of a GO layer. Excited by a red laser in a Kretschmann configuration, a significant GO influence on the electric field intensity (background of the cover) has been recorded, regardless of the distance among the cages. The system reached the resonance at an incident angle of 47° (diagram of reflectance, top left). The strong enhancement of the electromagnetic field induced by the GO layer influences the nonlinearity of the system and leads to Raman scattering. The analysis of the emitted signal of the on-resonance system allows the detection of the D and G peaks of the GO (diagram of transmission, top right).