Study On The Radiation Characteristics Of Dielectric Metasurface Based On Regulation Of Phase-Change Material Ge₂Sb₂Te₅ And Graphene

The dielectric metasurface has a wide range of applications in the fields of optical device integration,infrared thermal radiation,biological detection,etc.,due to its good process compatibility and novel radiation characteristics.Among them,the dielectric metasurface composed of high refractive index materials（such as Si and Ge）has attracted much attention of current metasurface research because of its low ohmic loss and strong optical performance.The function of the dielectric metasurface is fixed by the structure.If active and reconfigurable design can be carried out,the ability to dynamically adjust the electromagnetic field will better adapt to changes in application requirements.The optical properties of the phase-change material Ge₂Sb₂Te₅（GST）and graphene show obvious differences in different states,and this state transition is reversible.Based on the unique optoelectronic properties of GST and graphene,this work explores the active control spectral radiation characteristics of dielectric metasurface in the shortwave-infrared and near-infrared bands through reasonable structural design,combined with theoretical analysis and simulation research methods.Firstly,we have studied the Mie scattering theory and the basic theory of multipoles to explain the spectral radiation characteristics of metasurface.Taking spherical dielectric particles as an example,the Mie scattering coefficients are simplified and the scattering conditions of magnetic dipole and electric dipole resonances in Mie resonance are derived.The basic electromagnetic sources and multipole decomposition methods are introduced,and the calculation formulas of each multipole are given,which provides theoretical basis and method guidance for the research content of toroidal dipole resonance.Secondly,a tunable shortwave-infrared absorber made of the dielectric metasurface based on a Ge nanodisk array is proposed.By introducing the phase-change material GST layer,we can selectively and actively control the optical response.It is found that the narrowband absorption of 99.9%can be achieved for amorphous GST with an absorption depth of 54.6%at 1931 nm,which is attributed to the strong electric dipole resonance in the Ge nanodisk.The absorber enables a tunable operating wavelength by adjusting the geometric parameters to realize the spectral selectivity.In addition,the nanostructure,combined with a dielectric Bragg reflector with alternately stacked Si O₂ and Ti O₂ layers,can realize the switch from dual-band absorption for amorphous state to single-band absorption for crystalline state through the adjustment of electrical and magnetic resonances.Finally,a tunable near-infrared reflector made of the all-dielectric metasurface based on a double-Si-nano-ring array is proposed.The toroidal dipole resonance excited by the all-dielectric metasurface can achieve an ultra-narrowband reflection of 99.2%at 1333.5nm,and the high quality factor（Q）value reaches 889.By introducing the graphene layer and adjusting its chemical potential,the reflection at the resonance peak position can be attenuated to 25.3%and the reflection modulation depth is 73.9%.In addition,the optimal combination of size parameters is obtained by discussing the influence of size parameters on the reflection spectrum of the structure.