The Generation And Regulation Of Multipolar Fano Resonance In Asymmetrically Split Silver Nanorings/disks And Circular/three-opening Ring Nanodimers

Free electrons exist in metal conductors.These free electrons will move directional under the action of electric field force when we put conductors into electric field.Light is an electromagnetic wave.The incident direction,electric field and magnetic field directions of the light are perpendicular to each other.When the light shine on metal surface and the frequency of incident light equals to the oscillation frequency of free electrons,the surface plasmon resonances are generated.Surface palsmon resonances have attracted many researchers attention due to its unique optical properties,such as the near-field enhancements,Fano resonance,high refractive index sensitivity and etc.According to research results,surface plasmon resonances is sensitive to sizes,shapes,materials and refractive index of the nanostructure.We can modulation surface plasmon resonances effectively by changing above parameters.As far as the research status of surface plasmon resonances,there is still much room for development in the generation,regulation and application of multiple Fano resonances.Based on the previous studies on surface plasmon Fano resonances and the insufficient research on multiple Fano resonances,the asymmetric split ring-disk and the perfect ring-triple arcs ring nanostructures are proposed in this paper.We have theoretically explored the extinction characteristics,spectral modulation depth and potential application value of these two nanostructures.The article is mainly divided into four parts.In the first part,the basic theoretical knowledge and development history of surface plasmon system are introduced.In the second part,several numerical simulation methods for calculating the optical properties of micro-nanostructures are introduced.In the third and fourth part,asymmetric split ring-disk and perfect ring-triple arcs ring are mainly studied.Since the focus and highlight of this study are the third and fourth parts,a more detailed description of these two parts is given as follows.1.Asymmetric split ring-disk nanostructureIn this chapter,we proposed an asymmetric split ring-disk nanostructure,which exhibits rich optical properties.From the calculation results of the charge distributions,magnetic field enhancement and displacement current distributions,the magnetic Fano resonance is generated by the destructive interference between dark magnetic resonance mode(with almost zero net electric dipole moment)and bright electric resonance mode(with non-zero electric dipole moment).The magnetic Fano dip,electric and magnetic plasmon resonance modes can be effectively adjusted by changing the geometric parameters of the nanostructure.The magnetic double Fano resonances can be generated by rotating the whole nanostructure or splitting the disk along y axis.Compared with single Fano resonance,double Fano resonances can adjust multi-bands simultaneously.This characteristic can be used in multi-band spectrometer,controllable shaping of spectral lines and etc.2.Perfect ring-triple arcs ring nanostructureIn this chapter,a perfect ring-triple arcs ring naostructure is proposed and studied.According to the calculation results,the higher order dark modes of the perfect ring can be excited effectively by the triple arcs ring.And the double Fano resonances result from the coupling between the dark mode of perfect ring and the bright mode of the triple arcs ring.For this structure,we want breaking the structure's symmetry to see if it can achieve multiple Fano resonances.Through calculation,we found that the multiple Fano resonances can be excited by changing the center angle or width of the upper arc ring,where other geometric parameters unchanged.By further adjusting the above two parameters,the multiple Fano resonances show a good modulation depth.In addition,through offsetting the center of the triple arcs ring to destroy the symmetry of the nanostructure,multiple resonances modes will also be greatly excited.Here,the near-field enhancement distribution of these resonance modes becomes extremely uneven due to the symmetry breaking.The maximum enhancements of electric and magnetic fields reaching 409 and 40.8,respectively.Compared these nanostructure with the asymmetric split ring-disk nanostructures,the perfect ring-triple arcs ring can achieve more higher order multiple Fano resonances.And their applications are more extensive.