Multiple Fano Resonances In A Coupled Resonant System Of Crescent-cross Silver Nanostructures And Disk Waveguides

Surface plasmons have attracted the attention of researchers because of their rich optical properties.Surface plasmons can be divided into two types:one is restricted by metal nanostructures and can only be limited to the surface of metal nanoparticles,known as localized surface plasmons(LSPs).The other is surface plasmon polariton(SPPs)that propagate along the metal-dielectric interface.Local surface plasmons are excited in an external field under three-dimensional conditions.By changing the size,morphology,and polarization of light of nanostructures,precious metal nanoparticles have many unique optical properties,such as plasmon waveguides,surface-enhanced pull Mann scattering,electromagnetic induction transparency and Fano resonance effect.Surface plasmon polariton is studied in a two-dimensional region.Electromagnetic waves enter the waveguide to produce continuous and discrete states,which are then coupled to form the Fano resonance effect.The electromagnetic field at the Fano peak is confined within the cavity.These optical properties are widely used in ion filters,tunable ion separators and sensors.In recent years,great progress has been made in the study of surface plasmons,but the research on the Fano resonance effect and other optical properties has yet to be improved.We propose two types of silver crescent cross nanostructures based on local surface plasmons and disc-waveguide coupled resonance systems based on surface plasmons.The optical properties of these two types of surface plasmons are studied by simulation analysis.This article is divided into three parts:The first part introduces three numerical simulation methods of surface plasmon,including finite element method,finite difference time domain method and discrete dipole approximation method.The basic principles and characteristics of the finite element method are emphasized,and the other two simulation methods are briefly described.This article mainly uses the finite element method COMSOL Multiphysics software for simulation.In the second part,the optical properties of cross-shaped silver nanostructures based on the local surface plasmon Crescent crescent cross are studied.The split ring is one of the more common structures in plasmon nanostructures.Theoretically,the split ring(crescent)can increase the FOM value of the system due to its narrow and sharp structure.Adding a cross to the split ring,and rotating the cross in various ways can adjust its asymmetry in multiple directions.Simulation analysis,by changing the structural parameters to break the structural symmetry,can generate new plasmon magnetic modes and multiple Fano resonances,and can effectively regulate the spectrum,more energy is localized in the convexities and concaves of the structure.At the same time,by changing the angle between the two rods symmetrically,the FOM value can achieve a larger value,which has important applications in the field of sensing.In the third part,the optical properties of the disk waveguide coupled resonance system based on surface plasmon polariton are studied.The disc cavity is filled with ethanol.The two-dimensional finite element method was used to calculate the transmittance and magnetic field distribution of the system.The continuous state generated by the waveguide and the discrete state generated by the disc cavity are coupled with each other to form a dual Fano resonance.You can find more interesting optical characteristics by adjusting the parameters of the disc cavity.Adding triangular cavities,asymmetric disc cavities,triangular ring cavities,and circular cavities under the waveguide can achieve independent regulation of Fano resonance to different degrees,and the spectrum lines of the system can be adjusted by changing the temperature of ethanol.These optical characteristics of waveguide-coupled resonance systems have a wide range of applications in optical switches,plasma filters,tunable ion separators,and sensors.