Terahertz chiral metasurface with tunable VO ₂ dual-frequency phase transition: anomalous reflection and near-field encryption

Addressing the limitations of current chiral metasurfaces with narrow operational bandwidths and monotonous functionality, this paper proposes a dual-frequency phase-change tunable terahertz chiral metasurface device based on vanadium dioxide (VO 2 ). This innovation achieves functions such as anomalous reflection and near-field densification. This design employs temperature-controlled regulation of VO 2 conductivity to achieve strong circular dichroism (CD) responses of 0.81 and −0.82 at 3.17 and 3.87 THz, respectively. When arrayed, the metasurface generates approximately ±20 ∘ chiral anomalous reflection at both operating frequencies and supports near-field encryption imaging based on its mirroring properties. This device holds significant application value in the fields of terahertz absorption, polarization conversion, and chiral imaging.