Bifunctional tunable terahertz circular polarization converter based on Dirac semimetals and vanadium dioxide

We present a bifunctional polarization converter based on Dirac semimetals (DSMs) and vanadium dioxide (VO 2 ), which consists of two layers of DSMs on both sides, a metal grating and a VO 2 board. The polarization converter frequency is dynamically tuned by changing the Fermi energy level of the DSMs. The result suggests that when VO 2 is in an insulated state, the device behaves as a transmissive polarization converter. The dual-band transmissive polarization conversion and asymmetric transmission (AT) function of circularly polarized (CP) waves are realized at 1.99 THz and 3.46 THz, with the polarization converter ratio (PCR) reached 97.6% and 95.8%, respectively. In addition, when VO 2 is in the metal state, the designed polarization converter is a reflective device, which can maintain the chirality of the reflected CP wave to the incident wave in a wide band. The polarization-maintaining ratio (PMR) in the range of 2 THz to 3.55 THz is higher than 88%. When the angle of incidence is less than 60°, the frequency band of the PMR is narrowed and the amplitude reaches more than 90%.