A high-quality factor hybrid plasmonic nanocavity based on distributed Bragg reflectors

Herein,we propose a high-quality(Q) factor hybrid plasmonic nanocavity based on distributed Bragg reflectors(DBRs) with low propagation loss and extremely strong mode confinement.This hybrid plasmonic nanocavity is composed of a high-index cylindrical nanowire separated from a metal surface possessing shallow DBRs gratings by a sufficiently thin low-index dielectric layer.The hybrid plasmonic nanocavity possesses advantages such as a high Purcell factor(Fp) of up to nearly 20000 and a gain threshold approaching 266 cm~(-1)at 1550 nm,promising a greater potential in deep sub-wavelength lasing applications.     

Plasmonic effects and the morphology changes on the active material P3HT:PCBM used in polymer solar cells using Raman spectroscopy

There is no consensus yet that the enhancement effects of plasmonic device are predominantly caused by plasmonic effects or induced morphology changes in the optoelectronic `materials. Herein, we present a detailed Raman characterization of a typical organic P3HT:PCBM system comprising silver nanowires (Ag NWs) with different size, which can simultaneously study the plasmonic effects and the morphology changes. The direct comparison of the Raman spectra of non‐annealed and annealed samples indicates that the morphology of plasmonic samples has changed before annealing and the morphology of plasmonic samples and reference sample after annealing is not distinguishable. This indicates that the interaction between P3HT and Ag NWs with different size can be explained by plasmonic effects after annealing. Moreover, in‐situ Raman spectroscopy is used to study the morphology changes in plasmonic samples with different diameters of Ag NWs during heating process. This method can distinguish the plasmonic effects and morphology changes of plasmonic device. Copyright © 2016 John Wiley & Sons, Ltd.     

Plasmonic nanoparticle monomers and dimers: from nanoantennas to chiral metamaterials

We review the basic physics behind light interaction with plasmonic nanoparticles. The theoretical foundations of light scattering on one metallic particle (a plasmonic monomer) and two interacting particles (a plasmonic dimer) are systematically investigated. Expressions for the effective particle susceptibility (polarizability) are derived, and applications of these results to plasmonic nanoantennas are outlined. In the long-wavelength limit, the effective macroscopic parameters of an array of plasmonic dimers are calculated. These parameters are attributable to an effective medium corresponding to a dilute arrangement of nanoparticles, i.e., a metamaterial where plasmonic monomers or dimers have the function of “meta-atoms”. It is shown that planar dimers consisting of rod-like particles generally possess elliptical dichroism and function as atoms for planar chiral metamaterials. The fabricational simplicity of the proposed rod-dimer geometry can be used in the design of more cost-effective chiral metamaterials in the optical domain.     

Insulator—insulator—metal plasmonic waveguide for parasitic scattering suppression in plasmonic optics

We have shown using rigorous electromagnetic simulations that a planar structure consisting of two isotropic dielectric layers can be used to reduce parasitic scattering in plasmonic elements by an order-of-magnitude (to 1–3%). The proposed approach can be used for designing various plasmonic elements such as lenses, Bragg reflectors and plasmonic crystals.     

Stimulated emission of surface plasmon polaritons in a microcylinder cavity

We have observed stimulated emission of surface plasmon polaritons (SPPs) in dye-doped polymeric microcylinder cavities deposited onto gold and silver wires. The stimulated emission spectra featured a characteristic series of laser modes, with modal spacing corresponding to SPPs propagating at the interface between the metal and dielectric. A plasmonic microlaser adds to the toolbox of plasmonic devices and plasmonic metamaterials and enables on-chip plasmonic generation and loss compensation.     

Ultra-elongated depth of focus of plasmonic lenses with concentric elliptical slits under Gaussian beam illumination

In this paper, we discuss the influence of ratio of minor to major axis on the propagation property and focusing performance of a plasmonic lens with variant periodic concentric elliptical slits illuminating under a Gaussian beam. In order to analyse the influence theoretically, a finite-difference time-domain （FDTD） numerical algorithm is adopted for the computational numerical calculation and the design of the plasmonic structure. The structure is flanked with penetrated slits through a 200-nm metal film （Au） which is coated on a quartz substrate. Tunability of focusing capability of the plasmonic lenses is studied by tailoring the ratio. Our calculation results demonstrate that the ratio of the elliptical slits greatly affects the focusing capability of the lense. The plasmonic lenses with concentric elliptical slits illuminating under a Gaussian beam have ultra-elongated depth of focus. These results are very encouraging for the future study of the plasmonic lens-based applications.     

Light absorption measurement of a plasmonic photocatalyst in the circular plane waveguide of a photocatalytic dual light source spinning disk reactor

This study numerically investigates the light absorption of a plasmonic photocatalyst in the circular plane waveguide of a photocatalytic spinning disk reactor. The degradation of methyl orange (MO) in water with a dual light source spinning disk reactor (DL-SDR) and embedded diffusion coupler demonstrates the plasmonic photocatalytic reaction. When light propagates in the circular plane disk (CPD) waveguide of a DL-SDR, it gradually loses energy because of the absorption of the photocatalyst. This absorption boosts the processing efficiency of the plasmonic photocatalytic reaction. A real case by a diffusion coupler was used to present the plasmonic photocatalytic reaction. This study presents the numerical analysis of a secondary optical lens (SOL) coupler and the numerical evaluation of light absorption of the plasmonic photocatalyst in a DL-SDR. An elliptical reflector collects the light emitted from the circular ring edge of the SOL and CPD. This study presents an evaluation method that simulates the light absorption of a photocatalyst coating on the CPD of a DL-SDR.     

Low-threshold plasmonic lasing based on high-Q dipole void mode in a metallic nanoshell

We propose a novel type of plasmonic lasing nanostructure consisting of a metallic shell and a gain core. We demonstrate numerically that highly localized void modes of such metallodielectric core-shell nanoparticles have a very high quality factor. We found that the dipole void mode has a lasing threshold as low as 128 cm(-1) at 800 nm as a result of the unique mode distribution within the shell, due to a maximum field enhancement around the void center. The lasing condition for a symmetry-reduced silver nanocup is also investigated and the low plasmonic lasing threshold is sustained provided that the opening angle of the nanocup is smaller than 10°. Our proposal presents a new path toward plasmonic lasers with low gain threshold.     

Optical modes in a plasmonic waveguide with electrically anisotropic metamaterial

We study the optical modes in a plasmonic waveguide with electrically anisotropic metamaterial and dielectric, including symmetric (anti-symmetric) photonic mode and symmetric (anti-symmetric) plasmonic mode. The dispersion curves for these modes are derived, and a graphical method is used to calculate the solution of symmetric photonic mode and anti-symmetric plasmonic mode. By simulation results the conditions of the existence for these modes are deduced in each case.     

Easily coupled whispering gallery plasmons in dielectric nanospheres embedded in gold films

A new self-aligned robust method for coupling to whispering gallery modes (WGMs) of submicron microspheres utilizes their periodic arrangement without relying on nanopositioned external coupling devices. The microspheres are embedded in a nanostructured gold surface supporting delocalized plasmonic crystal modes that mediate the coupling, and can be tuned by the geometry. Detailed measurements of the angle- and orientation-dependent reflectivity reveal localized plasmonic WGMs whose energies scale with sphere diameter and agree closely with Mie calculations. Coupling between these plasmonic WGMs leads to mode splitting and the formation of plasmonic minibands of a controllable bandwidth.     

Influence of cavity geometry towards plasmonic gap tolerance and respective near-field in nanoparticle-on-mirror

In this work, we emphasize the importance of cavity geometry along with nanoparticle shape and plasmonic nanogap (based on a nanoparticle on a metallic film (NPOM) design) which plays significant role in understanding the complex plasmonic mode characteristics involving nanoparticle and gap mode resonances. The cross-section imprint of planar cavity on metallic film plays decisive role in near field enhancement properties at similar NP size and plasmonic nanogap conditions for spherical and cubical NPOM systems. By mimicking the NPOM structure to metal-insulator-metal design, we understand the resonant emission differences for the respective plasmonic modes. Influence of dominant and weaker gap mode resonances resulted in an interesting optical behavior (fluctuations in near field enhancement strength) in NP mode in case of cubical nanostructures. By such extensive investigation and interpretation of sub-wavelength complex plasmonic mode characteristics, various practical applications in plasmonics field can be accomplished.     

Theoretical study on the lasing plasmon of a split ring for label-free detection of single molecules and single nanoparticles

This paper reports the plasmonic lasing of a split ring filled with gain material in water. The lasing mode(1500 nm)is far from the pump mode(980 nm), which can depress the detection noise from the pump light. The laser intensities of the two modes simultaneously increase by more than 10~3 in amplitude, which can intensify the absorption efficiency of the pumping light and enhance the plasmonic lasing. The plasmonic lasing is a sensitive sensor. When a single protein nanoparticle(n = 1.5, r = 1.25 nm) is trapped in the gap of the split ring, the lasing spectrum moves by 0.031 nm, which is much larger than the detection limit of 10~(-5) nm. Moreover, the lasing intensity is also very sensitive to the trapped nanoparticle. It reduces to less than 1/600 when a protein nanoparticle(n = 1.5, r = 1.25 nm) is trapped in the gap.     

Binary TLBO algorithm assisted to investigate the supper scattering plasmonic nano rod

A new efficient binary optimization method based Teaching-Learning-Based Optimization (TLBO) algorithm is proposed to design an array of plasmonic nano-rods in order to achieve maximum scattering coefficient spectrum. In binary TLBO (BTLBO), a group of learner consists a matrix with binary entries; control the presence (“1”) or the absence (“0”) of nano-rods in the array. Simulation results show that scattering coefficient strongly depends on the localized position of nano-particles and non-periodic structures have more appropriate response in term of scattering coefficient. This approach can be useful in optical applications such as plasmonic nano-antenna.     

Direct imaging of localized surface plasmon polaritons

In this Letter, we report on dark field imaging of localized surface plasmon polaritons (SPPs) in plasmonic waveguiding bands formed by plasmonic coupled cavities. We image the light scattered from SPPs in the plasmonic cavities excited by a tunable light source. Tuning the excitation wavelength, we measure the localization and dispersion of the plasmonic cavity mode. Dark field imaging has been achieved in the Kretschmann configuration using a supercontinuum white-light laser equipped with an acoustooptic tunable filter. Polarization dependent spectroscopic reflection and dark field imaging measurements are correlated and found to be in agreement with finite-difference time-domain calculations.     

Binary teaching-learning-based optimization algorithm is used to investigate the superscattering plasmonic nanodisk

A new efficient binary optimization method based on Teaching-Learning-Based Optimization (TLBO) algorithm is proposed to design an array of plasmonic nanodisks in order to achieve maximum scattering coefficient spectrum. In binary TLBO (BTLBO), a group of learner consists of a matrix with binary entries; control the presence (‘1’) or the absence (‘0’) of nanodisks in the array. Simulation results show that scattering coefficient strongly depends on the localized position of nanoparticles and non-periodic structures have more appropriate response in term of scattering coefficient. This approach can be useful in optical applications such as plasmonic nanoantennas.     

Plasmon-induced transparency in metamaterials

A plasmonic "molecule" consisting of a radiative element coupled with a subradiant (dark) element is theoretically investigated. The plasmonic molecule shows electromagnetic response that closely resembles the electromagnetically induced transparency in an atomic system. Because of its subwavelength dimension, this electromagnetically induced transparency-like molecule can be used as a building block to construct a "slow light" plasmonic metamaterial.     

Surface plasmon polariton waveguides with subwavelength confinement

Surface plasmon polaritons(SPPs) are evanescent waves propagating along metal-dielectric interfaces, which provide an effective way to realize optical wave guiding with subwavelength confinement. Metallic nanostructures supporting SPPs,that is, plasmonic waveguides, are considered as required components to construct nanophotonic devices and circuits with a high degree of miniaturization and integration. In this paper, various types of plasmonic waveguides operating in the visible, infrared, and terahertz regions are reviewed, and the status of the research on their fundamentals, fabrications,and applications is provided as well. First, we discuss the mechanisms of SPPs beyond the diffraction limit, and their launching methods. Then, the characteristics of SPPs on various plasmonic waveguides are reviewed, including top-down and bottom-up fabricated types. Considering applications, certain prototypes of plasmonic devices and circuits constructed by plasmonic waveguides for bio/chemo sensing, router, and light modulation are demonstrated. Finally, a summary and future outlook of plasmonic waveguides are given.     

Stable Fano-like plasmonic resonance: its impact on the reversal of far-and near-field optical binding force

Even for a 100 nm interparticle distance or a small change in particle shape,optical Fano-like plasmonic resonance mode usually vanishes completely.It would be remarkable if stable Fano-like resonance could somehow be achieved in distinctly shaped nanoparticles for more than 1μm interparticle distance,which corresponds to the far electromagnetic field region.If such far-field Fano-like plasmonic resonance can be achieved,controlling the reversal of the far-field binding force can be attained,like the currently reported reversals for near-field cases.In this work,we have proposed an optical set-up to achieve such a robust and stable Fano-like plasmonic resonance,and comparatively studied its remarkable impact on controlling the reversal of near-and far-field optical binding forces.In our proposed set-up,the distinctly shaped plasmonic tetramers are half immersed(i.e.air-benzene)in an inhomogeneous dielectric interface and illuminated by?circular?polarized light.We have demonstrated significant differences between near-and far-field optical binding forces along with the Lorentz force field,which partially depends on the object’s shape.A clear connection is shown between the far-field binding force and the resonant modes,along with a generic mechanism to achieve controllable Fano-like plasmonic resonance and the reversal of the optical binding force in both far-and near-field configurations.     

Plasmonic atoms and plasmonic molecules

The proposed paradigm of plasmonic atoms and plasmonic molecules allows one to describe and predict the strongly localized plasmonic oscillations in the clusters of nanoparticles and some other nanostructures in uniform way. Strongly localized plasmonic molecules near the contacting surfaces might become the fundamental elements (by analogy with Lego bricks) for the construction of fully integrated opto-electronic nanodevices of any complexity and scale of integration. PACS 78.67.-n; 73.20.Mf; 32.50.+d     

Photonic bandgap plasmonic waveguides

A type of a plasmonic waveguide has been proposed featuring an "open" design that is easy to manufacture, simple to excite and offers convenient access to a plasmonic mode. Optical properties of photonic bandgap (PBG) plasmonic waveguides are investigated experimentally by leakage radiation microscopy and numerically using the finite element method confirming photonic bandgap guidance in a broad spectral range. Propagation and localization characteristics of a PBG plasmonic waveguide have been discussed as a function of the wavelength of operation, waveguide core size, and the number of ridges in the periodic reflector for fundamental and higher order plasmonic modes of the waveguide.