Fano Resonance And Higher-order Magnetic Modes Of Concentric Double-split Rings And Fish-like Dimer Metal Nanostructures

Surface plasmon photonics is a newly developed discipline in the field of photonics in recent years,because of its unique ability to manipulate light,which has been concerned by many people.Noble metals are the most commonly used materials in the study of surface plasmon,and some optical effects and mechanisms based on the surface plasmon of precious metals are still the research hotspot,such as Kerker effect,Hanle effect,Second harmonic,Fano resonance,Magnetic effect,etc.These effects have important application value in many fields.For example,Kerker effect can be used to control light by vibrating nanoparticles,which is very important for the operation of optical circuits;Magnetic moment imaging can be realized by using Hanle effect,which has played an important role in biomedical imaging,geological disaster prediction and so on;Second harmonic has been well applied in life science,industrial measurement and other different fields because of its microscopic imaging technology.In this paper,the optical effects of Fano resonance and magnetic resonance have been studied by us,and they have important application value in Fano switch,biosensor,Surface enhanced pectroscopy,negative refractive index materials and other fields.According to the development of surface plasmon and the previous research results in this field,a concentric double split ring nanostructures and a fish-like dimer nanostructures are studied in this paper,including their spectral characteristics and some physical effects.This paper is mainly composed of two parts:In the first part,the optical properties of concentric double split ring nanostructures are discussed and the optical properties of a fish like dimer nanostructure are studied in the second part.In the first section of this thesis,a nanostructure composed of two double split rings is designed and its optical properties are further studied.The results show that when the symmetry of the structure is destroyed along the x-axis and the y-axis,the double Fano resonance will be produced in the extinction spectrum.When the cavity of the inner split ring is biased,the absorption at the plasmon resonance peak will be suddenly weakened,and the electromagnetically induced transparent-like optical response will appear when the cavity is biased to a certain extent.In adiction,the resonance mode is sensitive to the surrounding refractive index,the maximum refractive index sensitivity(S)and the maximum figure of merit(FOM)at resonance mode can reach 1200 nm/RIU and 30.61.This series of excellent characteristics make it have potential application value in surface enhanced spectrum,biosensor,Fano switch,etc.In the second part of this thesis,a fish-like dimer nanostructure is proposed.The results show that when the structure is irradiated vertically by the incident light,a asymmetric Fano line-shape will be excited in the extinction spectrum.When the structure is rotated,some new plasmon resonance modes will be excited,and the second,fourth and sixth order magnetic modes can be observed in a same spectrum.In addition,when we increase the number of semi-ring in the dimer gap,the higher-order magnetic modes in the spectrum can be excited regularly,and the magnetic field in the resonance mode will also be enhanced.The maximum enhancement of the magnetic field can be 49 times of the incident light,which makes our structure can be well used in the study of surface enhanced spectroscopy and negative refractive index materials.