Multifunctional chiral metasurface for broadband dual-channel asymmetric cross-polarization transmission, perfect absorption, and sensing

Abstract This paper introduces a double-layer chiral metamaterial composed of orthogonal S-shaped resonators, designed for multifunctional applications in the terahertz regime. Numerically demonstrated, the metasurface exhibits distinct operational modes. In the transmission mode, it enables broadband dual-channel asymmetric cross-polarization conversion and transmission. Specifically, in forward propagation, Channel 1 (0.49–1.10 THz, 76.7% fractional bandwidth) converts x - to y -polarized waves with an efficiency exceeding 78%, while simultaneously suppressing the reverse conversion. Conversely, Channel 2 (1.44–1.90 THz, 27.5% fractional bandwidth) performs the opposite polarization conversion ( y - to x -polarization) and transmission while suppressing its counterpart. This asymmetric behavior is reversed under backward wave incidence, with a maximum asymmetric transmission coefficient of 0.89. In reflection mode, the structure achieves perfect absorption of CP waves, with absorption ratios as high as 0.995 for RCP and 0.952 for LCP at two distinct frequencies, demonstrating strong chirality. Furthermore, the absorption resonance exhibits a predictable spectral shift in response to variations in the thickness and refractive index of an overlaying analyte film. This sensitivity suggests the platform’s strong potential for high-performance terahertz sensing applications.