Confinement Of Surface Plasmon Polaritons Research Articles

A Tunable artificial plasmonic nanolaser with wide spectrum emission operating at room temperature

Abstract With information and communication technology developing fast, a key objective in the field of optoelectronic integrated devices is the reduction of nano-laser size and energy consumption. Photonics nanolasers are unable to exceed the diffraction limit and typically exhibit low modulation rates of several GHz. In contrast, plasmonic nanolaser utilize highly confined surface plasmon polariton (SPP) modes that can surpass diffraction limit and their strong Purcell effect can accelerate the modulation rates to several THz. Here, we propose a parametrically tunable artificial plasmonic nanolasers based on Metal-Insulator-Semiconductor-Insulator-Metal (MISIM) structure, which demonstrates the capability to compress the mode field volume to λ/14. As the pump power increases, the proposed artificial plasmonic nanolasers exhibits wide output spectrum of 20nm. Additionally, we investigate the impact of various cavity parameters on the nanolaser’s output threshold, offering potentials for realizing low-threshold artificial plasmonic nanolasers. Moreover, we observe a blue shift in the center wavelength of the nanolaser output with thinner gain layer thickness, predominantly attributed to the increased exciton–photon coupling strength. Our work brings inspiration to several areas, including Spaser-based interconnects, Nano-LEDs, spontaneous emission control, miniaturization of photon condensates, eigenmode engineering of plasmonic nanolasers, and optimal design driven by Artificial Intelligence (AI).

Plasmon-enhanced circular dichroism spectroscopy of chiral drug solutions.

We investigate the potential of surface plasmon polaritons at noble metal interfaces for surface-enhanced chiroptical sensing of dilute chiral drug solutions with nl volume. The high quality factor of surface plasmon resonances in both Otto and Kretschmann configurations enables the enhancement of circular dichroism differenatial absorption thanks to the large near-field intensity of such plasmonic excitations. Furthermore, the subwavelength confinement of surface plasmon polaritons is key to attain chiroptical sensitivity to small amounts of drug volumes placed around ≃100 nm by the metal surface. Our calculations focus on reparixin, a pharmaceutical molecule currently used in clinical studies for patients with community-acquired pneumonia, including COVID-19 and acute respiratory distress syndrome. Considering realistic dilute solutions of reparixin dissolved in water with concentration ≤5 mg/ml and nl volume, we find a circular-dichroism differential absorption enhancement factor of the order ≃20 and chirality-induced polarization distortion upon surface plasmon polariton excitation. Our results are relevant for the development of innovative chiroptical sensors capable of measuring the enantiomeric imbalance of chiral drug solutions with nl volume.

Toward Magneto‐Plasmonic Functionality in a Self‐Assembled Device Based on Colloidal Synthesis

The confinement of surface plasmon polaritons (SPPs) offers strong field strengths also for longitudinal field components. Phenomena like spin‐momentum locking can thus be exploited for novel functionality in nanodevices. External control of transport or directional coupling of propagating SPPs would be highly interesting for applications. Herein, the coupling of noble metal and magnetic nanoparticles to a silver nanowire acting as SPP waveguide using a hybrid self‐assembly approach is demonstrated. A designated setup is reported to isolate and investigate magnetically controlled transport in such devices. Various configurations are measured to quantify the required sensitivity for the typically tiny magnet response at moderate strengths of the magnetic field. Although magnetic control cannot be achieved, the required improvements can be estimated based on a heuristic numerical model. It is suggested using an approach to enhance magnetic response using a combination of metal and magnetic nanoparticles. Such devices can be assembled in principle with self‐assembly approach in a multistep process.

Rational design of a ZnO nanowire laser on a surface plasmon polariton.

Plasmonic lasers, which use the strong confinement of surface plasmon polaritons, are key parts to realize ultracompact coherent light sources at deep subwavelength scales. We propose a plasmonic laser composed of a silicon substrate, ZnO nanowire, dielectric layer, metal layer, and electrode. In this structure, the superimposed coupling of the surface plasmon mode at the metal interface with the high refractive index gain nanowire mode makes the electric field in the spacer layer significantly enhanced. The ZnO nanowire is used as gain material to provide gain compensation. The optical and electrical properties are simulated with the geometric parameters and dielectric layer material. The results show that the structure has strong confinement of the optical field and can realize a deep subwavelength constraint at a lower threshold level. It provides theoretical support for realizing ultracompact coherent light sources.

High-quality multi-band absorber in a hybrid all-dielectric system using the surface plasmon polaritons

High confinement of surface plasmon polaritons in graphene have important applications in many aspects. In this paper, we have demonstrated that high-quality multi-band absorption can be achieved by using a hybrid system where periodic monolayer graphene nanoribbons is coated on an all-dielectric nanostructure. The effect of the monolayer graphene nanoribbons on plasmonic resonances absorption is investigated theoretically and numerically. It is found that the high tunability and large near field enhancement of the system is observed by changing the grating period and Fermi level. After delicate optimization, the system can achieve high-Q resonances in the vicinity of the bound states in the continuum, and the Q factors of the two resonance modes are respectively significantly enhanced (＞450, 600). In addition, the multi-band light absorption enhancement with high quality can be observed by altering the carrier mobility of graphene. Wherein the optimized absorption efficiency up to 97% is reached. More interestingly, the proposed structure puts up palpable advantage in absorption stability when the incident angle is varied from 0° to 60°. Thus, this work may facilitate the design of high-performance optoelectronic devices based on all-dielectric configuration, such as tunable optical sensors and perfect absorbers.

Accurate Time-Domain Modeling of Arbitrarily Shaped Graphene Layers Utilizing Unstructured Triangular Grids

The accurate modeling of curved graphene layers for time-domain electromagnetic simulations is discussed in the present work. Initially, the advanced properties of graphene are presented, focusing on the propagation of strongly confined surface plasmon polariton waves at the far-infrared regime. Then, the implementation of an unstructured triangular grid was examined, based on the Delaunay triangulation method. The electric-field components were placed at the edges of the triangles, while two different techniques were proposed for the sampling of the magnetic ones. Specifically, the first one suggests that the magnetic component is placed at the triangle’s circumcenter providing more accurate results, although instability may occur for nonacute triangles. On the other hand, the magnetic field was sampled at the triangle’s centroid, considering the second technique, ensuring the algorithm’s stability, but further approximations were required, leading to a slight accuracy reduction. Moreover, the updating equations in the time-domain were extracted via an appropriate approximation of Maxwell equations in their integral form. Finally, graphene was introduced in the computational domain as an equivalent surface current density, whose location matches the corresponding electric components. The validity of our methodology was successfully performed via the comparison of graphene surface wave propagation properties to their theoretical values, whereas the global error determination indicates the minimal triangle dimensions. Additionally, an instructive setup comprising a circular graphene scatterer was analyzed thoroughly, to reveal our technique’s advantages compared to the conventional staircase discretization.

Investigation of a new graphene strain sensor based on surface plasmon resonance

The high confinement of surface plasmon polaritons in graphene nanostructures at infrared frequencies can enhance the light-matter interactions, which open up intriguing possibilities for the sensing. Strain sensors have attracted much attention due to their unique electromechanical properties. In this paper, a surface plasmon resonance based graphene strain sensor is presented. The considered sensing platform consists of arrays of graphene ribbons placed on a flexible substrate which enables efficient coupling of an electromagnetic field into localized surface plasmons. When the strain stretching is applied to the configuration, the localized surface plasmon resonance frequency sensitively shift. The strain is then detected by measuring the frequency shifts of the localized plasmon resonances. This provides a new optical method for graphene strain sensing. Our results show that the tensile direction is the key parameter for strain sensing. Besides, the sensitivity and the figure of merit were calculated to evaluate the performance of the proposed sensor. The calculated figure of merit can be up to two orders of magnitude, which could be potentially useful from a practical point of view.

Highly Confined Surface Plasmon Polaritons from Graphene Quantum Cherenkov Effect

Highly confined surface plasmon polaritons (HC-SPPs) can significantly enhance light-matter interaction and dramatically shrink electronic or photonic systems, including x-ray sources. However, due to the short wavelength and low phase velocity of HC-SPPs, traditional approaches have a hard time exciting them. Here electron-beam excitation of hot carriers plus the quantum Cherenkov effect in graphene are predicted to yield monochromatic HC-SPPs at 1/300 of the vacuum wavelength, with the Fermi energy of graphene dynamically tuning the frequency. Thus one can realize a compact x-ray source without artificial periodic structures, pointing ultimately to tabletop x-ray systems.

Ultracompact Photodetection in Atomically Thin MoSe2

Excitons in atomically thin semiconductors interact very strongly with electromagnetic radiation and are necessarily close to a surface. Here, we exploit the deep-subwavelength confinement of surface plasmon polaritons (SPPs) at the edge of a metal–insulator–metal plasmonic waveguide and their proximity of 2D excitons in an adjacent atomically thin semiconductor to build an ultracompact photodetector. When subject to far-field excitation we show that excitons are created throughout the dielectric gap region of our waveguide and converted to free carriers primarily at the anode of our device. In the near-field regime, strongly confined SPPs are launched, routed and detected in a 20 nm narrow region at the interface between the waveguide and the monolayer semiconductor. This leads to an ultracompact active detector region of only ∼0.03 μm2 that absorbs 86% of the propagating energy in the SPP. Due to the electromagnetic character of the SPPs, the spectral response is essentially identical to the far-field regime, exhibiting strong resonances close to the exciton energies. While most of our experiments are performed on monolayer thick MoSe2, the photocurrent-per-layer increases super linearly in multilayer devices due to the suppression of radiative exciton recombination. These results demonstrate an integrated device for nanoscale routing and detection of light with the potential for on-chip integration at technologically relevant, few-nanometer length scales.

Room Temperature Electrically Driven Ultraviolet Plasmonic Lasers

AbstractPlasmonic lasers, which make use of the strong confinement of surface plasmon polaritons (SPPs), are key components to realize ultracompact coherent light sources at deep subwavelength scale. Currently, large metal and radiation losses of their metallic cavities limit electrically driven plasmonic lasers operation mainly at cryogenic temperature, where sufficient gain can be obtained. It is a crucial challenge to accomplish high performance electrically driven plasmonic lasers operated at room temperature. Benefiting from the large exciton binding energy and large oscillator strength of zinc oxide (ZnO) gain media, an optically pumped ultraviolet (UV) plasmonic laser is demonstrated from a hybrid metal–insulator–semiconductor structure, in which a magnesium oxide (MgO) gap layer plays a critical role in reducing the metallic loss. Further optimizing the thickness of the MgO gap layer and ZnO active layer, room temperature electrically driven UV plasmonic lasers with a threshold of 70.2 A cm‐2 are realized for the first time under the injection of electrical carriers through the metallic electrode of the hybrid structure. Localizing light in subwavelength dimension, this novel type of UV plasmonic nanolasers may find various applications in photolithography, sensing, integrated microfluidic systems for surface sterilizations and nanoscale treatment processes.

Strong Localization of Surface Plasmon Polaritons with Engineered Disorder.

In this work, we experimentally demonstrate for the first time strong localization of surface plasmon polaritons (SPPs) at visible regime in metallic nanogratings with short-range correlated disorder. By increasing the degree of disorder, the confinement of SPPs is significantly enhanced, and the effective SPP propagation length dramatically shrinks. Strong localization of SPPs eventually emerges at visible regime, which is verified by the exponentially decayed fields and the vanishing autocorrelation function of the SPPs. Physically, the short-range correlated disorder induces strong interference among multiple scattered SPPs and provides an adequate fluctuation to effective permittivity, which leads to the localization effect. Our study demonstrates a unique opportunity for disorder engineering to manipulate light on nanoscale and may achieve various applications in random nanolasing, solar energy, and strong light-matter interactions.

Surface Plasmonic Lattice Solitons in Semi-Infinite Graphene Sheet Arrays

We investigate the surface plasmonic lattice solitons (PLSs) in semi-infinite graphene sheet arrays. The surface soliton is formed as the SPPs tunneling is inhibited by the graphene nonlinearity, and meanwhile the incident power should be above a threshold value. Thanks to the strong confinement of surface plasmon polaritons (SPPs) on graphene, the effective width of surface PLSs can be squeezed into deep-subwavelength scale of ~ 0.001{\lambda}. Based on the stable propagation of surface PLSs, we find that the light propagation can be switched from the array boundary to the inner graphene sheets by reducing the incident power or increasing the chemical potential of graphene. The study may find promising application in optical switches on deep-subwavelength scale.

Plasmonic lattice solitons in nonlinear graphene sheet arrays.

We investigate the plasmonic lattice solitons (PLSs) in nonlinear graphene sheet arrays (GSAs) composed of spatially separated graphene sheets embedded in dielectric. Both the nonlinearities of graphene and dielectric are considered. The self-focusing PLSs at the Brillouin zone edges can be yielded by balancing the normal diffraction of surface plasmon polaritons (SPPs) via either the nonlinear effect of graphene or self-focusing dielectric. The self-defocusing PLSs corresponding to anomalous diffraction of SPPs at the Brillouin zone center could be yielded by the nonlinearity of self-defocusing dielectric alone. The width and propagation distance of the PLSs are dependent on the period of the GSAs and the chemical potential of graphene. Thanks to the strong confinement of SPPs, the PLSs in GSAs can be squeezed into an effective width as small as λ/250. The study may find applications in optical circuits and switches on deep-subwavelength scale.

Long ranging and weakly confined surface plasmon polaritons via free space excitation

Surface plasmon polaritons (SPPs) on a planar metal/dielectric interface can confine the electromagnetic energy beyond diffraction limit at the cost of a small propagation length, which is typically of micrometer scale in the visible regime. This paper investigates the possibility to increase the propagation distance via metamaterial whose dielectric constant can be designed at will. It is found that the longer propagation distance due to the smaller dielectric constant is accompanied with a larger decay length into the dielectric. Furthermore, three simple configurations via free space coupling technique were proposed, while the end-fire excitation can also be applied efficiently. This work has a potential application to channel energy over large distances between different plasmonics components in the future design of integrated photonic chips and circuits.

Cherenkov radiation via surface plasmon polaritons excitation by an electron beam in a layered metal-dielectric structure

Recently great attention and interest have been paid to the enhanced Cherenkov light radiation transformed from surface plasmon polaritons, excited by a uniformly moving electron bunch in a structure of thin metal film with dielectric-medium loading. This paper proposes a modified structure with a dielectric film covered above the metal film of aforementioned structure, which can improve the radiation characteristics by its effective manipulation on the dispersion property of surface plasmon polaritons. The required exciting electron beam energy for generation of light radiation from visible to ultraviolet frequency regime is dramatically lowered. Furthermore, the radiation power density reaches several times that of the original one due to stronger confinement of surface plasmon polaritons on the metal film. The dependence of radiation characteristics including radiation frequency and power density on the permittivity and thickness of dielectric film are studied in detail. The lower exciting electron beam energy and higher radiation power density of the modified structure will facilitate the practical application of a coherent, tunable and compact integrated light radiation source.

Dye-assisted gain of strongly confined surface plasmon polaritons in silver nanowires.

Noble metal nanowires are excellent candidates as subwavelength optical components in miniaturized devices due to their ability to support the propagation of surface plasmon polaritons (SPPs). Nanoscale data transfer based on SPP propagation at optical frequencies has the advantage of larger bandwidths but also suffers from larger losses due to strong mode confinement. To overcome losses, SPP gain has been realized, but so far only for weakly confined SPPs in metal films and stripes. Here we report the demonstration of gain for subwavelength SPPs that were strongly confined in chemically prepared silver nanowires (mode area = λ(2)/40) using a dye-doped polymer film as the optical gain medium. Under continuous wave excitation at 514 nm, we measured a gain coefficient of 270 cm(-1) for SPPs at 633 nm, resulting in partial SPP loss compensation of 14%. This achievement for strongly confined SPPs represents a major step forward toward the realization of nanoscale plasmonic amplifiers and lasers.

Controlling the polarization orientation of highly confined and enhanced surface plasmon polaritons

We show the manipulation of the overall polarization orientation of the enhanced and confined surface plasmon polaritons near the nanostructure.

Coupling of a dipolar emitter into one-dimensional surface plasmon

Quantum plasmonics relies on a new paradigm for light–matter interaction. It benefits from strong confinement of surface plasmon polaritons (SPP) that ensures efficient coupling at a deep subwavelength scale, instead of working with a long lifetime cavity polariton that increases the duration of interaction. The large bandwidth and the strong confinement of one dimensional SPP enable controlled manipulation of a nearby quantum emitter. This paves the way to ultrafast nanooptical devices. However, the large SPP bandwidth originates from strong losses so that a clear understanding of the coupling process is needed. In this report, we investigate in details the coupling between a single emitter and a plasmonic nanowire, but also SPP mediated coupling between two emitters. We notably clarify the role of losses in the Purcell factor, unavoidable to achieve nanoscale confinement down to 10−4(λ/n)3. Both the retarded and band-edge quasi-static regimes are discussed.

Excitation and Active Control of Propagating Surface Plasmon Polaritons in Graphene

We demonstrate the excitation and gate control of highly confined surface plasmon polaritons propagating through monolayer graphene using a silicon diffractive grating. The normal-incidence infrared transmission spectra exhibit pronounced dips due to guided-wave resonances, whose frequencies can be tuned over a range of ~80 cm(-1) by applying a gate voltage. This novel structure provides a way to excite and actively control plasmonic waves in graphene and is thus an important building block of graphene plasmonic systems.

Low-threshold optical bistability in metal-nonlinear dielectric multilayer nanostructure

We numerically investigate the optical bistability with highly confined surface plasmon polaritons (SPPs) modes excitation in a metal-nonlinear dielectric multilayer nanostructure. We find that the field distribution forms a standing wave through the excitation of coupled SPPs in nanomultilayers caused by the Fabry-Perot interferometer. In addition, the average field amplitude is increased by a factor of ∼20.6 compared to that of the incident beam. A very low bistability threshold of 2.75 MW/cm2 is obtained with a fundamental SPPs mode excitation at the telecommunication wavelength of 1550 nm.