| Metamaterial,a kind of artificial material composed of sub wavelength meta-atoms,can effectively regulate the phase,amplitude and polarization of electromagnetic wave in subwavelength scale,its structural characteristics make us manipulate electromagnetic wave uniquely.Surface plasmon polaritons(SPPs)are surface electromagnetic modes generated by the interaction between electromagnetic wave and transferable surface charge,which have the characteristics of very strong field binding and near-field enhancement.Electromagnetic regulation becomes more flexible and convenient by introducing SPPs into metamaterials.The metamaterial perfect absorber based on SPPs has great application prospects in photoelectric detection,filtering,sensing,energy storage and holographic imaging,etc.However,its operating frequency is often limited by the structure shape,size and arrangement of units,and it is difficult to realize active control.In this paper,surface plasmon materials such as graphene and vanadium dioxide(VO2)are introduced into metamaterial absorbers.Based on the framework of electromagnetic theory,finite-difference time-domain methods are used to conduct in-depth research on metamaterial perfect absorption and performance regulation,aiming at providing strategies for the design of new absorbers and providing theoretical and scientific basis for the development of actively tuned photonic devices in the future.The research contents and conclusions of this paper are as follows:1.A novel tunable compact multi-band coherent perfect absorber(CPA)based on graphene and VO2 is designed,where square VO2 particle array in the structure is symmetrically distributed on both sides of the polysilicon-SiO2-graphene-SiO2-polysilicon structure.It is found that the absorber has three absorption peaks,which are derived from the plasmon resonance modes of graphene and VO2 particles,and have unique near-field distributions and bandwidths.Besides of the phase difference between the two coherent beams,the Fermi energy level of graphene and the surrounding temperature can all effectively control the absorption peak.In addition,the absorber has polarization insensitivity and high sensitivity to changes in surrounding refractive index.Compared with the existing CPAs,our designed CPA have more freedom of active regulation,which is helpful for the design of actively tunable and multifunctional nano plasma devices and metamaterials including absorbers,optical switches and filters.2.A terahertz metamaterial absorber with tunable spin selectivity based on VO2 is proposed.A VO2 resonator consisting of a Z-antenna and a conducting microrod is periodically arranged on a SiO2-gold substrate.The results show that the chiral structure when VO2 is in high temperature can achieve spin selective absorption of electromagnetic waves with a frequency of 3.36THz.Specifically,it can perfectly absorb left-handed circularly polarized(LCP)light,but reflects most of right-handed circularly polarized(RCP)light,and its circular dichroism(CD)reaches 74%.The physical mechanism is the electric dipole interaction of the top antenna.The CD of the metamaterial can be adjusted actively by changing the surrounding temperature(i.e.changing the conductivity of VO2),and the modulation depth of CD reaches 0.74.When the chiral structure is in the dielectric phase at room temperature,the metamaterial structure can be regarded as a conventional mirror,reflecting most of the circularly polarized light and changing its spin direction.More importantly,our designed metamaterial carrying encrypted information have good imaging results and can be applied to thermal-controlled imaging,this design provides an opportunity to flexibly control the spin-selective encryption platform used to encode keys. |
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