Generation of Multiple Fano Resonances in Plasmonic Split Nanoring Dimer

We present a computational study of the plasmonic response of a split nanoring dimer resonator which supports multiple plasmonic Fano-like resonances that arises by the coupling and interference of the dimer plasmon modes. For the generation of Fano resonances with large modulation depths, numerous configurations of the dimer resonator are analyzed which are observed to be highly dependent on the polarization of incident light. Moreover, the influence of dimension of the split nanoring structure on the spectral positions and intensities of the higher order Fano resonances are also investigated, and it is found that the asymmetric Fano line shapes can be flexibly tuned in the spectrum by varying various geometrical parameters. Such Fano resonators are also discovered to offer high values of figure of merit and contrast ratio due to which they are suitable for high-performance biological sensors.     

Higher Order Tunable Fano Resonances in Multilayer Nanocones

We present a computational study of the plasmonic response of a gold–silica–gold multilayered nanostructure based on truncated nanocones. Symmetry breaking is introduced by rotating the nanostructure and by offsetting the layers. Nanocones with coaxial multilayers show dipole–dipole Fano resonances with resonance frequencies depending on the polarization of the incident light, which can be changed by rotating the nanostructure. By breaking the axial symmetry, plasmonic modes of distinct angular momenta are strongly mixed, which provide a set of unique and higher order tunable Fano resonances. The plasmonic response of the multilayered nanocones is compared to that of multishell nanostructures with the same volume and the former are discovered to render visible high-order dark modes and to provide sharp tunable Fano resonances. In particular, higher order tunable Fano resonances arising in non-coaxial multilayer nanocones can vary the plasmon lines at various spectral regions simultaneously, which makes these nanostructures greatly suitable for plasmon line shaping both in the extinction and near field spectra.     

High-Q Fano Resonances in Asymmetric and Symmetric All-Dielectric Metasurfaces

We present high-quality (high-Q) Fano resonances in all-dielectric metasurfaces consisting of a periodic array of air holes on silicon (Si) film, deposited on the top of quartz substrate. With the control of the radius difference Δr and center distance Δd between the air holes, two asymmetric all-dielectric metasurfaces are proposed to achieve extremely high-Q Fano resonances. Numerical method with finite difference time domain and equivalent circuit model is employed to analyse the excitation mechanism of the sharp Fano resonances. It is shown that the high-Q Fano resonances come from the interference of two Fabry-Perot resonances, resulting in an extremely narrow window. Moreover, we also demonstrate that the high-Q Fano resonances can also be realized as electromagnetic wave is obliquely incident on the symmetric all-dielectric metasurface. Finally, we show the high-Q Fano resonances caused by asymmetric configurations can coexist with the Fano resonances in the symmetric configuration induced by oblique incidence. As a result, a tri-band Fano resonance is obtained. It is expected that our results will provide important mechanisms for tuning and switching a wide variety of optical devices such as angular sensors, filters, switches, and modulators.     

Plasmonic Fano Resonances in Single-Layer Gold Conical Nanoshells

Plasmonic Fano resonances arise in symmetric single-layer conical nanoshells, which can be switched on and off by changing the polarization of the incident electric field. By breaking the symmetry, higher-order dark hybridized modes emerge in the spectrum, which couple to the superradiant bright mode and induce higher-order plasmonic Fano resonances. From a comparison with spherical nanostructures, it comes out that single-layer conical nanoshells are found to be highly capable in the generation of higher-order Fano resonances with larger modulation depths in the optical spectra. Such nanostructures are also found to offer high values of figure of merit and contrast ratio due to which they are highly suitable for biological sensors.     

Efficient Modulation of Multipolar Fano Resonances in Asymmetric Ring-Disk/Split-Ring-Disk Nanostructure

Plasmonics - Generation of multiple Fano resonances are theoretically investigated in asymmetry ring-disk and asymmetry split-ring-disk. The effects of structural parameter on multiple Fano...     

Excitation of Multiple Fano-Like Resonances Induced by Higher Order Plasmon modes in Three-Layered Bimetallic Nanoshell Dimer

The presence of plasmonic Fano-like resonances in the optical response of isolated and dimer metal-dielectric-metal nanostructures are investigated theoretically. The nanostructures are engineered in such a way to support multiple Fano-like resonances that are induced by the interference of bright and dark plasmon modes. It is found that the dimer resonators exhibit different types of Fano resonances for both the transverse and longitudinal polarizations unlike conventional nanodimers. Several configurations of the dimer Fano resonator are analyzed with special emphasis on the Fano spectral line shape. Breaking the symmetry of the dimer nanostructure in various directions control the asymmetric line shape and provides different kinds of unique Fano resonances. In certain cases, the Fano resonators exhibit multiple Fano resonances that are particularly significant for plasmon line shaping and can serve as platforms for multi-wavelength sensing applications.     

Tunable Fano Resonance Based Mode Interference in Waveguide-Cavity-Graphene Hybrid Structure

In this paper, a graphene strip is introduced into a metal-insulator-metal (MIM)-integrated square cavity hybrid structure; the transmission spectra are theoretically investigated by the finite different time domain (FDTD) methods. An asymmetric Fano resonance dip that has high figure of merit (FOM) value appears in the transmission band. According to the multimode interference coupled mode theory (MICMT) analytical method, the Fano resonance originates from the coherent coupling between TM₁₀ cavity magnetic mode and graphene plasmonic resonance electric mode. The center wavelength, full width at half maximum (FWHM), and FOM value of the Fano resonance can be tuned dynamically by altering the Fermi level of the graphene. Through breaking the symmetry of the hybrid structure or introducing double graphene strips with different Fermi level into hybrid structure, double Fano resonance are realized. This study can provide some theoretical basis and design reference for designing ultrahigh sensitivity plasmonic sensor.

     

Electromagnetically Induced Transparency and Sharp Asymmetric Fano Line Shapes in All-Dielectric Nanodimer

Low-loss electromagnetically induced transparency (EIT) and asymmetric Fano line shapes are investigated in a simple planar silicon dimer resonator. The EIT and Fano effects emerge due to near-field coupling of the modes supported by both the nanoparticles in a dimer structure. Different configurations of the dimer nanostructure are analyzed, which provide distinct EIT and Fano resonances. Furthermore, the tunability of EIT and Fano resonant modes are incorporated by changing the structural parameters. It is also found that the dimer resonator exhibits high Q factor and large electromagnetic field enhancement at Fano resonance and EIT window due to extremely low absorption loss. Such values and narrow resonances are supposed to be useful highly sensitive sensors and slow-light applications.     

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.     

Magnetic-Based Fano Resonance by a Trimer with Y-shaped Gap

We introduce a Y-shaped gap into a silver disk to break the structure symmetry which can be looked as a loop-linked structure. Magnetic resonances are excited by incident light when incident electric field is parallel to the trimer plane. Fano resonance is generated by the coupling between bright electric mode and dark magnetic mode. These resonances can be adjusted by tuning the gap size, the radius of trimer, and the position of Y-shaped gap. The extinction cross section of the structure is calculated with the finite element method (FEM). The maximum figure of merit (FOM) is 37.8. Both the magnetic and electric field are greatly enhanced at the Fano dip and the magnetic resonance peak.     

Tunable Fano Resonances in Mid-Infrared Waveguide-Coupled Otto Configuration

A planar silicon carbide/dielectric multilayer structure is investigated in Otto geometry, where surface phonon polaritons and planar waveguide mode can be coupled to realize Fano resonances under transverse magnetic polarization. The resonance coupling is analytically demonstrated using the coupled harmonic oscillator model and numerically presented through rigorous coupled-wave analysis calculations, which shows that the coupling strength between different resonances and the resonant wavelength matching condition plays an important role in the bandwidth and position of the Fano resonance (FR); the magnetic field distribution was also shown to explain the origin of FRs qualitatively.

     

Tunable Ultrahigh Order Surface Plasmonic Resonance in Multi-Ring Plasmonic Nanocavities

Optical properties of multi-ring with spatial symmetry breaking are investigated theoretically. Tunable ultrahigh order surface plasmonic resonance is achieved, which is found to be sensitive to geometric parameters. Certain high-order surface plasmonic resonances can be either suppressed or enhanced when geometrical parameters are adjusted. Moreover, more than one quadrupolar-dipolar, octupolar-dipolar, and hexadecapolar-dipolar mode of the surface plasmonic resonance can be achieved. The asymmetry also allows the generation of strong electric field enhancement with these nanostructures that can be applied in the field of surface-enhanced spectroscopy and biosensing.     

Fano Resonances Induced by Strong Interactions Between Dipole and Multipole Plasmons in T-Shaped Nanorod Dimer

A simple T-shaped plasmonic nanostructure composed of two perpendicular coupled nanorods is proposed to produce strong Fano resonances. By the near-field coupling between the “bright” dipole and “dark” quadrupole plasmons of the nanorods, a deep Fano dip is formed in the extinction spectrum, which can be well fitted by the Fano interference model. The effects of the geometry parameters including nanorod length, coupling gap size, and coupling location to the Fano resonances are analyzed in detail, and a very high refractive index sensitivity is achieved by the Fano resonance. Also by adjusting the incident polarization direction, double Fano resonances can be formed by the interferences of the dipole, quadrupole, and hexapole plasmons. The proposed nanorod dimer structure is agile, and a trimer which supports double Fano resonances can be easily formed by introducing a third perpendicular coupled nanorod. The proposed T-shaped nanorod dimer structure may have applications in the fields of biological sensing and plasmon-induced transparency.     

Tunable Localized Hybrid Plasmon Modes and Fano Resonances in Au Core-Semishell

Plasmonics - We present a numerical study of the plasmonic properties of Au core-semishell. Symmetry breaking in semishell results in a dipole–quadrupole Fano resonance without the offset of...     

Subradiant,Superradiant Plasmon Modes and Fano Resonance in a Multilayer Nanocylinder Array Standing on a Thin Metal Film

The optical properties of a novel nanostructure consisting of a hexagonal array of aligned vertically three-layered metal-dielectric-metal nanodisks on a silver film are theoretically studied through the finite-difference time-domain method. The novel nanostructure exhibits three obvious optical transmission bands due to the excitation of subradiant plasmon modes, superradiant plasmon modes, and Fano resonances. Surface plasmon polaritons of the underlying Ag film also play a significant role on these three optical transmission bands via coupling with localized surface plasmons of nanodisk pairs. Moreover, the nanostructure also exhibits a good tunability of optical response by modifying the sizes of cylinders, the thickness of underlying metal film, and the dielectric constant of middle layer. These results demonstrate the nanostructure with great advantages in optical sensors and filters.

     

Rhodium Plasmonics for Deep-Ultraviolet Bio-Chemical Sensing

Rhodium (Rh) has been recently introduced as a perfect metal for ultraviolet (UV) applications with the advantages of its oxide-free nature and support of strong plasmon resonant modes at very short wavelengths. We report on a simple platform of nanoplasmonic structures to support strong plasmonic Fano resonances across the deep-UV spectrum for biochemical sensing applications. We investigate the plasmonic response of several types of Rh nanoparticles and designed dimer-type antennas using nanorings with geometrical tunability in both symmetric and antisymmetric assemblies. Using numerical and theoretical methods, it is shown that Rh-based dimer antennas with broken symmetry can be tailored to support strong plasmon resonant modes at the deep-UV region (\( E>6\; eV \)). We also propose a complex infinity-shaped structure composed of a pair of split rings with a nanodisk in between with extra degree of tunability to push the plasmon resonant modes further in deep-UV spectrum. Plasmon hybridization theory is used to describe formation of plasmonic Fano-resonant dips in simple nanoscale assemblies. We calculate the corresponding figure of merit for the Rh-based nanostructure around 11.5 which shows an excellent sensitivity to the refractive index perturbations of the surrounding medium at very short wavelengths for sensing applications.     

Tuning the Fano Resonance Between Localized and Propagating Surface Plasmon Resonances for Refractive Index Sensing Applications

Localized and propagating surface plasmon resonances are known to show very pronounced interactions if they are simultaneously excited in the same nanostructure. Here, we study the Fano interference that occurs between localized surface plasmon resonance (LSPR) and propagating surface plasmon polariton (SPP) modes by means of phase-sensitive spectroscopic ellipsometry. The sample structures consist of periodic gratings of gold nanodisks on top of a continuous gold layer and a thin dielectric spacer, in which the structural dimensions were tuned in such a way that the dipolar LSPR mode and the propagating SPP modes are excited in the same spectral region. We observe pronounced anti-crossing and strongly asymmetric line shapes when both modes move to each other’s vicinity, accompanied of largely increased phase differences between the respective plasmon resonances. Moreover, we show that the anti-crossing can be exploited to increase the refractive index sensitivity of the localized modes dramatically, which result in largely increased values for the figure-of-merit which reaches values between 24 and 58 for the respective plasmon modes.     

Tunable Multi-Fano Resonances in MDM-Based Side-Coupled Resonator System and its Application in Nanosensor

In this paper, two Fano resonances are achieved in the proposed plasmonic system. Theoretical analysis and simulation results show that two discrete states coupled with a continua lead to these Fano resonances. The discrete states are provided by the side-coupled square cavity, and a baffle plate placed in metal-dielectric-metal waveguide is used to produce a continuous transmission spectrum. The resonant wavelengths and the linewidth of these Fano resonances can be easily tuned by adjusting the parameters of system. This system exhibits high sensitivities as high as 850 and 1120 nm/RIU corresponding to two Fano resonances, and the figure of merit can reach to 1.7 × 10⁵ by optimizing the system. By introducing another square cavity, four Fano resonances are obtained which originate from four discrete states coupled with continua, and they can be tuned independently. The flexible multi-Fano resonances system has significant application bio-nanosensor, nonlinear, and slow light devices.     

Magneto-Electric Double Fano Resonances in Hybrid Split Ring/Disk Hetero-Cavity

In this work, we conceive and demonstrate the magneto-electric double Fano resonances of a hetero-cavity composed of Si disk and Au split ring, where Si disk can provide additional magnetic responses besides electric responses. The interference between electric and magnetic responses in proposed hetero-cavity gives rise to magneto-electric double Fano resonances with magnetic and electric near-field enhancements. Dipole radiative enhancement is used to analyze magnetic and electric responses of hetero-cavity and the spectral features of hetero-cavity can be used to quantitatively characterize by coupled oscillator model. And the spectral tunability of magneto-electric double Fano resonances is investigated, highlighting a potential for applications in low-loss sensing and nanophotonic devices.     

Highly Sensitive Plasmonic Sensor Based on Fano Resonance from Silver Nanoparticle Heterodimer Array on a Thin Silver Film

We investigate the optical spectrum of a multilayer metallic slab using multiple-scattering formalism. A thin silver film is attached to a periodic array of heterodimers consisting of two vertically spaced silver nanoparticles of different radii. Depending on the radius of nanoparticles, heterodimer array presents a simple nanoscale geometry which gives rise to remarkable plasmonic properties of multipolar resonances. Due to the coherent interference of the localized nanoparticle plasmons (discrete mode) and surface plasmon polaritons of metallic film (continuous mode), the reflection spectrum represents a sharp asymmetric Fano resonance dip, which is strongly sensitive to the refractive index of the surrounding embedded dielectric host. The physical features contribute to a highly efficient plasmonic sensor for refractive index sensing with sensitivity of ～1.5?×?10^?3 RIU/nm.