Broadband switchable terahertz half-/quarter-wave plate based on metal-VO₂ metamaterials

We propose a metal-vanadium dioxide (VO₂) metamaterial with broadband and functionality-switchable polarization conversion in the terahertz regime. Simulation results show that the function of the proposed metamaterial can be switched from a half-wave plate (HWP) to a quarter-wave plate (QWP) over a broad bandwidth of 0.66-1.40 THz, corresponding to a relative bandwidth of 71.8%. The HWP obtained when VO₂ is in the insulating state has reflection of 90% and linear polarization conversion ratio exceeding 98% over the bandwidth of 0.58-1.40 THz. By transiting the phase of VO₂ into the conducting state, the obtained QWP can convert the incident linearly-polarized wave to circularly-polarized wave with an ellipticity of 0.99 over 0.66-1.60 THz. Additionally, results show that the proposed broadband switchable HWP/QWP has a large angular tolerance. We expect that this broadband and switchable multi-functional wave plate will find applications in polarization-dependent terahertz systems including sensing, imaging, and telecommunications.