Angularly Stable Terahertz Metasurface with Multi-Frequency Narrowband Cross-Polarization Conversion and Broadband Quarter Waveplate Function

Precise manipulation of terahertz (THz) wave polarization is essential for enabling high-performance THz imaging, wireless communication, and spectroscopy. However, existing birefringent and metasurface-based polarization controllers typically offer either cross-polarization conversion or waveplate functionality and often operate over limited bandwidths with restricted angular tolerance. In this work, we experimentally demonstrate a compact, dual-functional reflective metasurface that unifies high-efficiency narrowband cross-polarization conversion with wideband quarter-wave plate (QWP) operation. Both simulations and measurements confirm near-unity cross polarization conversion at 0.65, 0.80, 2.02, and 2.48 THz, as well as QWP bands at 0.86–1.95 THz (fractional bandwidth (FBW) 77%) and 2.08–2.45 THz (FBW 16%). The measured results further reveal high polarization efficiency and angular stability up to 50°, validating the metasurface’s practical potential. This experimentally verified design offers a significant step toward multifunctional, compact, and broadband THz polarization-control components for next-generation THz systems.