Manipulation of cross-polarization conversion and unidirectional reflectionlessness by VO2 in a terahertz metamaterial

We present a bilayer design in a terahertz metamaterial consisting of two triangular resonators that can manipulate broadband cross-polarization conversions and three-band unidirectional reflectionlessnesses by using the phase-change material VO₂ for the incidence of linearly and circularly polarized waves. When VO₂ is in metallic state, the broadband cross-polarization conversion effects are realized in range of 0.41 THz\(\sim \)0.54 THz and the polarization conversion ratio reaches \(\sim \)1. We also find that the proposed structure has the ability to convert linear polarizations into circular polarizations at 0.39 THz and 0.59 THz. When VO₂ is in insulator state, three-band unidirectional reflectionlessnesses are attained at 0.50 THz, 0.72 THz and 0.81 THz based on Fabry–P\({\mathrm{\acute{e}}}\)rot resonant coupling between the upper and lower triangular resonators.