Fano Resonances Of Silver Square Split Ring Dimers And Silicon Square Hole Disk Nanostructures

Optical nanostructures have excellent wave front control capabilities and become an effective method to solve the bottleneck of traditional optical components.With the development of some advanced nano-processing technologies represented by electron beam lithography,optical nanostructures with flexible design freedom have been realized in large-scale preparation in practical applications.Therefore,the optical metasurface formed by optical nanostructures is effectively used in important fields such as optical holographic imaging,polarization conversion,nonlinear optics and metalens.Fano resonance is a resonance phenomenon with an asymmetrical linear pattern.When the nanostructure generates Fano resonance,the radiation loss of the whole structure is low,a huge electromagnetic field enhancement can be obtained,and it is very sensitive to changes in the refractive index of the environment.These good characteristics make Fano resonance widely studied in the fields of surface-enhanced spectroscopy,near-field enhancement,biosensing,etc.The generation of Fano resonance based on various nanostructures is a hot research topic in nanophotonics.In this paper,a plasmon nanostructure and a dielectric nanostructure are designed.The finite element method(FEM)is used to study the optical properties of the two structures when they generate Fano resonance.The main research work is as follows:In the first part of the text,a silver square split ring dimer(SSRD)nanostructure was designed,and the optical properties and applications of the pure magnetic Fano resonance based on plasmon resonance were studied.The results show that the interaction between the SSRD nanostructure and incident light can obtain a toroidal dipolar(TD)resonance mode generated by a pair of magnetic dipole resonances with opposite magnetic dipole moments.At the same time,the pure magnetic Fano resonance can be effectively excited and adjusted by changing the symmetry of the SSRD nanostructure,so that the electromagnetic field energy is effectively limited and a strong magnetic field enhancement can be obtained in a specific area.The SSRD nanostructures with different parameters can also exhibit good refractive index sensitivity to different refractive index environments,which indicates that SSRD nanostructures have potential value in becoming sensors.In the second part of the text,a periodic square hollow nano disk(SHND)based on dielectric silicon material was designed,and the characteristics of multi-Fano resonance with high quality factor and high modulation depth produced by the structure were studied.The results show that by moving the position of the hollow,the symmetry of the SHND nanostructure can be changed and the transition from a single Fano resonance to three Fano resonances can be achieved.Then,adjusting the geometric parameters such as the height and side length of the SHND nanostructure can effectively adjust the position of Fano resonance,and it can make the three Fano resonances obtain more than 70 times of electric field enhancement and magnetic field enhancement while maintaining a high Q-factor value and a modulation depth close to 100%.In the first part of this article,the SSRD nanostructure based on metal plasmon resonance can be used to design the refractive index sensor while obtaining Fano resonance;in the second part,the dielectric silicon-based SHND nanostructure has low ohmic loss and diverse magnetic resonance modes,provides a way to produce ultra-high Q value,ultra-high near-field enhancement and multi-Fano resonance.