Tunable chiral metasurface for spin-selective absorption and reflective focusing effect for terahertz wave based on vanadium dioxide (VO2)
Yan Shen, Yanfang Xiao, Lingling Yang, Ling Wu, Bin Cai, Hui Luo, Yongzhi Cheng, Xiangcheng Li
Abstract
• This paper proposes a tunable chiral metasurface (CMS) composed of double-asymmetric-split-rings (DASRs) structure integrated with VO 2 pads adhered on a dielectric substrate backed with a metal ground plane. • The designed tunable CMS with VO 2 at insulating state ( σ VO₂ = 2×10 2 S/m) can achieve absorbance of 99.5% for RHCP wave and 93.0% for LHCP wave at 2.39 THz and 3.07 THz, respectively. • Increasing the conductivity of VO 2 from 2×10 2 S/m to 2×10 5 S/m allows continuous adjustment of the CD value at 2.39 THz and 3.07 THz within ranges of 0 to 0.75 and 0 to -0.86. • The designed MS can achieve a reflective focusing effect with tunable efficiency for the incident LHCP wave and high absorption for the RHCP wave at 3.07 THz. In this paper, a tunable reflective chiral metasurface (CMS) based on vanadium dioxide (VO₂) is proposed for spin-selective absorption and reflective wavefront manipulation in the terahertz (THz) regime. The CMS unit cell comprises a double-asymmetric-split-rings (DASRs) structure integrated with VO₂ pads, adhered to a dielectric substrate and backed by a metallic ground plane. Numerical simulations reveal that, in the insulating state of VO₂ (σ VO₂ = 2×10² S/m), the CMS achieves exceptional spin-selective absorption efficiency with absorbance of 99.5% for right-handed circularly polarized (RHCP) waves at 2.39 THz and 93.0% for left-handed circularly polarized (LHCP) waves at 3.07 THz. This performance yields notable circular dichroism (CD) values of ±0.74 and ±0.86 at 2.39 THz and 3.07 THz, respectively. Leveraging the Pancharatnam–Berry (PB) phase principle, the design enables full 360 ° reflection phase modulation through DASR orientation angle adjustment. Theoretical analyses confirm simultaneous realization of high spin-selective absorption and independent wavefront control for orthogonal circular polarization at identical frequencies. As a proof-of-concept, a CMS prototype is numerically validated to exhibit high LHCP absorption and RHCP reflected focusing at 3.07 THz. This multifunctional CMS platform offers promising potential for advancing wireless communication systems, polarization-encoded signal processing, and chiral spectroscopy applications.