Broadband Angularly Stable Polarization Conversion in Terahertz Band via Vertically Stacked Frequency Selective Surface Metasurface

This paper introduces a compact three-layer metasurface polarization converter for efficient bidirectional transverse electric (TE) to transverse magnetic (TM) mode conversion in the terahertz (THz) regime. The design overcomes critical limitations of conventional converters—narrow bandwidth and angular sensitivity—using vertically stacked copper split-ring resonators (SRRs) on a silicon substrate. Through optimized phase and resonance tuning, the metasurface achieves > 90% polarization conversion efficiency across a broad 1–1.8 THz bandwidth while maintaining robust performance for incidence angles up to 60°. Full-wave simulations validate its angular insensitivity and bidirectional functionality, with surface current and field analyses elucidating the multi-resonance mechanism. Fabrication feasibility is ensured via standard copper/SiO₂ deposition and photolithography processes. This high-performance, readily integrable design advances THz applications requiring dynamic polarization control, including communications, imaging, and sensing systems.