Triple-band tunable terahertz circular dichroism in a VO 2 -based asymmetric double-E metasurface absorber

Most chiral metamaterial absorbers operate in a single band with limited circular dichroism (CD) tunability. Here, a VO 2 -based asymmetric double-E (ADE) metasurface absorber is proposed to realize strong and dynamically tunable multiband CD in the terahertz regime. The structure consists of a patterned VO 2 layer, a SiO 2 spacer, and a metallic ground plane, where mirror symmetry is broken by unequal arm lengths. Pronounced absorption contrast between left- and right-circularly polarized waves is achieved at 0.984, 1.147, and 1.338 THz, with CD values approaching ±0.98. By tuning the VO 2 conductivity, large CD amplitude modulation is obtained at all resonance bands, while polarization rotation enables complete CD sign reversal, leading to chirality inversion. Stable triple-band CD is maintained for incident angles up to 30°. Furthermore, the metasurface exhibits high refractive index sensitivity, with a maximum sensitivity of 1536 GHz/RIU, enabling multiband detection of low-concentration analytes. This work may provide a useful reference for applications in terahertz multiband chirality manipulation, active polarization control, and high-sensitivity sensing.