Absortpion And Polarization Properties Of Biaxial Hyperbolic Material Metasurfaces Based On α-MoO₃

Metasurfaces（MSs）are ultrathin,artificially engineered materials made of subwavelength building blocks.Supporting the integration and miniaturization of optical components,and controls the amplitude,phase,and polarization of reflected and transmitted waves.In recent years,MSs have realized many interesting physical effects,among which absorption MSs and polarization control MSs have attracted much attention.Hyperbolic materials have also been extensively reported in the field of MSs research due to their unique optical properties.α-phase molybdenum trioxide（α-MoO₃）,as a biaxial hyperbolic crystal,has metallic or dielectric properties on different crystal axes,and can exhibit both out-of-plane and in-plane hyperbolic properties.Three distinct hyperbolic wavelength regions are exhibited on three orthorhombic crystal axes.In addition,the hyperbolic wavelength region ofα-MoO₃ is wider.Therefore,α-MoO₃ exhibits the potential to achieve perfect absorption and control the polarization properties of electromagnetic waves.In this paper,the finite element software COMSOL is used for simulation calculation,and the perfect absorber and polarization converter based onα-MoO₃ are designed.The following are the main research contents:1.As an anisotropic crystal,α-MoO₃ has different dielectric functions in the three orthorhombic directions.The dielectric function form when the crystal axis and the crystal surface are at an angle is theoretically deduced,and the transmittance,reflectivity and polarization conversion rate of the thin filmα-MoO₃ when the crystal axis rotates at different angles are simulated by COMSOL software.Theα-MoO₃/Si O₂ superlattice polarization converter was designed,and the influence of the structural unit parameters and the number of unit layers on the transmission polarization conversion rate was studied.The results show that the polarization converter can realize the complete conversion of the TM incident wave to the TE transmitted wave,which has application prospects in the research direction of polarization control.2.A polarization-dependent absorption MSs based onα-MoO₃was designed.The TE wave and TM wave absorptivity of the MSs were calculated by the COMSOL software,and it was concluded that the metasurface could achieve broadband absorption of TE wave and narrow-band absorption of TM wave.Furthermore,the absorptivity ofα-MoO₃ layer,patternedα-MoO₃/dielectric bilayer structure,α-MoO₃/dielectric/gold triple-layer structure,and patternedα-MoO₃/dielectric bilayer structure are compared.Then,the relationship between the geometric parameters of the MSs and the incident angle and the absorptivity are analyzed,and the structure of the MSs unit is optimized.Finally,the effect of crystal axis orientation on the MSs is discussed.