Dual-function tuneable asymmetric transmission and polarization converter in terahertz region

Abstract

Abstract We theoretically demonstrated a switchable, as well as tuneable, asymmetric transmission and reflective polarization conversion device in terahertz region. The proposed dual-function device composed of vanadium dioxide (VO2) and Dirac semimetal (DSM) metamaterials (MMs). Switching is achieved by exploiting the dielectric-to-metal phase transition of VO2 board. On the one hand, the hybrid MMs structure behave as a transmission device when VO2 board in its insulating phase and VO2 grating in its metallic phase. In this case, broadband asymmetric transmission of linear polarization has been realised in the range of 2.023-5.971 THz. On the other hand, this hybrid metamaterial acts as a reflective device when VO2 board in its metallic phase and VO2 grating in its insulating phase. In this situation, linear-to-circular polarization conversion has been achieved in the ranges 2.058-3.423 and 4.753-5.6 THz, and at 6.496 THz. In each of the above working modes, tuneable spectral response has been achieved by modifying the Fermi energy of DSM materials. The device also exhibits a robust polarization conversion performance with the incident angle less than 40°. Dual-function metamaterial like the one presented here may find applications in active polarization controller, asymmetric transmission device, broadband and multiband filters, and other tuneable modulators.