We propose a three layered metal-graphene-metal metasurface to investigate the controllable linear asymmetric transmission and perfect polarization conversion in THz regime, by using the finite-difference time-domain (FDTD) method. An on-to-off control of asymmetric transmission and perfect polarization conversion is achieved by changing the Fermi energy of graphene from 0.8 eV to 0 eV. We present the electric field distribution and Fabry-Perot-like cavity model to analyze the working mechanisms. By gradually shifting the Fermi energy of graphene, two functions are realized, i.e., controllable linear asymmetric transmission and controllable total transmission with near perfect polarization conversion.

We propose a planar optical bilayered chiral metamaterial, which consists of periodic metallic arrays of two L-shaped structures and a nanorod twisted on both sides of a dielectric slab, to investigate the optical chirality breaking effect by using finite-difference time-domain (FDTD) method. Even the metamaterial is with chiral symmetry, an optical chirality breaking window in the asymmetric transmission pass band is obtained in chiral metamaterial structure. We analyze the plasmonic mode properties and attribute the mechanism of the optical chirality breaking effect to the plasmonic analogue of EIT. The optical chirality breaking window can be modulated by changing the geometric parameters of the nanorods in the structure.

We propose a graphene and strontium titanate (STO) integrated terahertz metasurface that can achieve the flexible manipulation of plasmon-induced transparency (PIT) effect. The proposed structure consists of a doped Si substrate, a SiO₂ spacer, and a STO film with graphene antennas and Indium-Tin-Oxide (ITO) nanowhiskers electrodes patterned on it. By separately biasing the graphene antennas, the bright-bright mode coupled PIT effect is achieved. By flexibly configuring the Fermi energy distributions on the graphene antennas, the shape of PIT spectrum is also flexibly manipulated. Moreover, the working frequency band can be shifted by changing the environmental temperature due to the temperature dependent permittivity of the STO film. Our findings are beneficial in designing flexibly manipulated THz devices.

We propose a planar THz hybrid bulk Dirac semimetal (BDS)-metal metamaterial which consists of a hybrid BDS-metal array on a dielectric layer and a back metallic mirror. The simulation results show that a spectral window that possesses high reflectance with no polarization conversion effect arises in the polarization conversion pass band due to the existence of the BDS rods. Interestingly, though the proposed structure possesses no symmetry property, the effects are nearly the same for x- and y-polarization incidences. We analyze the electric field distributions at the breaking frequency and attribute the phenomena to plasmonic analogue of electromagnetically induced reflectance (EIR-like) effect for x-polarization incidence and direct back scattering for y-polarization incidence. The dependence of the breaking window on the BDS rod length shows that, for both x- and y-polarization incidences, the breaking characteristic is mainly determined by the dipole resonance on the BDS rod. Moreover, the breaking window can be independently and dynamically manipulated by changing the Fermi energy of the BDS rods. Our results may provide potential applications in designing new polarization control devices.