Plasmon Fano Resonant Modes Excitation And Coupling Of Metamaterials

Surface plasmon is a kind of electron evanescent wave generated by the coincident resonance between the photons and free elect rons on the metal surface.Surface plasmon polaritons are waves that propagate along the surface of a conductor,which has been theoretically and experimentally proven to confine the electromagnetic field below the diffraction limit.It has attracted huge interest because of its advantages of breaking through the traditional diffraction limit.It is worth noting that metal nanoparticles support local surface plasmon resonance,accompanied by electron oscillating,resulting in energy localization and enhancement.Therefore,metamaterials composed of nanoparticles of different sizes and shapes have special optical properties.It is necessary to study and analyze the resonant modes supported by different metamaterials.However,the metals have the features of inevitable losses while the dielectrics are low-loss.To improve the quality factors,dielectric metamaterials have been widely researched and applied.Considering the synthetical properties of two materials,a rational design to combine the dielectrics with metals to enhance the interaction between light and matter.The combined optical and electronic properties of this configuration benefit from the local plasmonic resonance in metals.In this paper,we will discuss the excitation of quadrupole mode,high quality factors of Fano resonances and the modulation of Fano resonances.The main contents of this paper are as follows:(1)The plasmonic system composed of a defective silver nanostrip and a complete silver nanostrip is theoretically investigated to achie ve two Fano resonances.A quadrupole mode cannot be directly excited on a complete n anostrip,while it can be fulfilled by introducing the defect.This defective silver nanostrip supports both of the superradiant dipole and quadrupole modes,which produce bright-dark coupling and detuning modes mechanisms and further result in two asymmet ric Fano dips in the transmission spectrum.Moreover,the Fano resonance characteristics in the two nanostrips can be tuned by modulating the gap distance between the two n anostrips,the parameters of the defect,and the electric-field polarization angle.In addition,plasmon induced transparency(PIT)is a special Fano resonance.We analyze quadrupole mode as superradiant to excite the proximity nanostrip.Our research realizes multiple PIT resonances in the nanostructure,which may have interesting applications of plasmonic switching devices in highly integrated circuits.(2)We demonstrate the existence of Fano resonance in a system of nanoring stacked by a half nanoring.Our proposed scheme exploits the stacked method und er normal incidence to excite the subradiant mode.This stacked nanostructure can support multiple high-quality Fano resonances in spectral,which can be as high as 114.By rotating the half nanoring,the nanostructure has a new rotation mode and high tunability,providing a dynamic control of plasmonic spectral response.High-quality resonant line shapes corresponding to the different order modes of Fano structures are readily achieved at near-infrared wavelengths,which is a benefit to the application for nanosensor in highly integrated circuits(3)Metamaterials made from coupled nanostrips with stubs demonstrate electromagnetically induced transparency(EIT)resonances under the condition of symmetry and asymmetry.We exploit novel approaches of presenting the phenomenon by using the near-field coupling between two specific radiative resonances to generate two distinct EIT windows within a relative short wavelength range.We use the Hamiltonian coupling model to explain the EIT resonances.Furthermore,the nanostructures provide a tunable control of plasmonic spectral response through modulating the related parameters.The multi-channel selectable EIT windows based on these coupling effects are realized in this metamaterial,which may have potential applications in highly composite circuits.(4)Integrated silicon nanostrip with silver nanofilm can cause silicon nanostrip's drastic optical resonances and strengthen the capacity of light absorption.Here,w e describe the optical properties of silicon nanoarrays on a thin silver film for extreme light confinement at subwavelength nanoscales.Surface plasmon resonances of the silver nanofilm can affect the displacement current of the silicon nanostrips,resulting in two magnetic dipole resonances,that is,the magnetic quadrupole resonances of dielectric silicon nanostrips in the visible regions.The resonant field of the dielectric nanostrip engages the screening response of the silver film,resulting in plasm on resonance configuration and thus achieving perfect light absorption in the dielectric nanostrip.Moreover,we can attain similar results in other nanostructures,such as silicon cylinder and rhombus column arrays.By breaking the symmetry of nanostructure,we also achieve high-performance multispectral Fano resonance,whose quality factor is 1254,and almost perfect absorption effect of dielectric metamaterials under the normal incidence of light.Because it can sustain hybridized plasmon modes and magnetic modes,the combined system will benefit the application of solar energy accumulation.