Research On Resonant Modes With High Quality Factor Based On All-dielectric Metasurfaces

The metasurfaces composed of unit cells in the subwavelength scale can effectively control the amplitude,phase and polarization of electromagnetic wave,and realize novel optical effects such as negative refraction,ideal lens and electromagnetic cloaking.The metal metasurfaces can excite the surface plasmon resonances,but their large radiation loss limits the Q factor.The all-dielectric metasurfaces can excite a series of Mie resonances.These resonances have high quality factors and strong capabilities of confining electromagnetic field,which have been widely used in surface Raman enhancement,sensing and nonlinear optics and other fields.This paper explores and studies the resonant modes in the all-dielectric metasurfaces.Firstly,simulations and analyses of all-dielectric metasurfaces.The structures are numerically simulated based on the finite element method.The resonant modes in the alldielectric metasurfaces are studied by combining Mie scattering theory and multipolar decompositions method.Secondly,the anapole mode based on the Φ-shaped silicon disk is studied.The characteristics and physical mechanisms of the anapole mode in the two cases of Φ-shaped silicon disk particle and array are analyzed.The simulation results show that the array can greatly improve the Q factor of the anapole mode.In addition,the adjustments of structure parameters to the optical characteristics of the anapole mode in the Φ-shaped silicon disk array are discussed.Finally,an I-Φ shaped all-dielectric metasurface is proposed.This design can realize the asymmetric excitations of two high Q factor resonances.Through the multipolar decompositions and electromagnetic field distributions of the double resonances,it is verified that the double resonances are a toroidal dipole(TD)resonance and a magnetic dipole(MD)resonance,respectively.The influences of structure asymmetry on double resonances are emphasized.It not only explores the physical sources of double resonances,but also reveals the physical mechanism of quasi-bound state in the continuum(quasi-BIC)in the asymmetric metasurface.Finally,the refractive index sensing performances of the double resonances are studied.The refractive index sensitivities of the two resonances reach 784.8 nm/RIU and 630 nm/RIU,respectively.Thus,excellent sensing effects are obtained.In this paper,we propose an effective way to manipulate TD resonance and quasiBIC MD resonance with high Q factor,which broaden the ideas for obtaining stronger resonant modes,and provide the possibility for applications in enhancing nonlinear effects,sensing and nanolasers.