Study On Fano Resonance Effect Of Surface Plasmon In Metallic Nanostructures

Collective oscillations of free electrons in the metal nanoparticles — surface plasmons(SP),has very unique optical properties,and thus can localize optical fields at the surface of nanoparticles and enhance light-matter interactions at the nanoscale.Now the study on SP is gradually developing into a new subject — plasmonics.This thesis theoretically studies the Fano resonance phenomenon caused by the SP resonance coupling effect in metal nanostructures,and innovatively propose two new schemes for generating Fano resonance.We design two kinds of metallic nanostructures,which support Fano resonance.The present metallic nanostructures have important applications in sensors,optical switching devices and so on.In this thesis,we first introduce the basic concepts of surface plasmons,the principle and application of SP.Secondly,the Fano resonance and electromagnetic calculation method for plasmonic nanostructures and matematerials are introduced.Finally,this thesis innovatively proposes two new schemes for generating Fano resonance based on SP resonance coupling effect.The content of the thesis mainly includes the following two aspects:1.We study theoretically light transmission through a silver film perforated with an array of split-ring resonator(SRR)shaped apertures.An asymmetric lineshape,which is characteristic of the Fano resonance,has been found in a narrow frequency range of the spectrum.The effect can be attributed to the interference between propagating surface plasmon polaritons(SPPs)on the silver film and magnetic plasmon polaritons(MPPs)associated with the SRR-shaped apertures.An anticrossing behavior of the resonance positions has also been observed in the transmission spectra,demonstrating the strong coupling of the SPPs with the MPPs.Due to the steep dispersion of the Fano resonance profile,the plasmonic nanostructure proposed could find important applications in sensors,switching,and nonlinear and slow-light devices.2.We theoretically investigate the diffraction coupling of magnetic plasmon(MP)resonances of three-dimensional(3D)metamaterials composed of a rectangular array of metallic vertical splitring resonators(VSRRs).We show that through suspending the 3D metamaterials into air to decrease the effect of substrate,the interaction of MP resonances excited in the VSRRs with a collective surface mode signaled by Wood anomaly in the periodic arrays can result in a narrow-band mixed mode with greatly enhanced magnetic fields.The interaction can also lead to an interesting anticrossing phenomenon similar to Rabi splitting observed in atomic physics,which is well explained by a coupled oscillator model.Importantly,because the enhanced magnetic fields localized in VSRR gaps at this mixed mode resonance are lifted off from substrate and can be fully exposed to the sensing medium,our designed 3D metamaterials have high sensing performance factors(S =900 nm/RIU,FOM =38,and FOM* =125).The huge magnetic field enhancement and high sensing sensitivity make the designed 3D metamaterials promising for label-free biochemical sensing.