Dual‐Band Terahertz Polarization Conversion Enabled by 3D‐Printed Anisotropic Metasurfaces

ABSTRACT

Extending dual‐ or multi‐band wave plates to the terahertz regime remains challenging due to the complex design of high‐efficiency metasurfaces and the scarcity of scalable, low‐cost fabrication techniques. Here, we overcome this limitation by demonstrating a dual‐band metasurface‐based half‐wave plate (HWP) with an out‐of‐plane triple‐bar design, where single‐ and double‐bar pillars are vertically stacked at distinct heights within a single meta‐atom. Simulations reveal that the low‐frequency band is primarily governed by magnetic resonances of the single‐bar pillar, while the high‐frequency band arises from hybrid magnetic‐electric resonances involving the double‐bar pillars. The HWPs are fabricated using a simple projection micro‐stereolithography (PµSL) 3D printing technique. Experimental results show a polarization conversion ratio exceeding 90% across 0.33–0.78 THz (fractional bandwidth, FBW = 81.1%) and 1.29–1.81 THz (FBW = 33.5%). Moreover, by simply tuning the pillar height, the same platform yields quarter‐wave plate behavior with ellipticity exceeding 0.8 across 0.49–0.83 THz (FBW = 51.5%) and below ‐0.8 across 1.14–1.85 THz (FBW = 47.5%). This out‐of‐plane metasurface approach, combined with a simple 3D printing process, establishes a scalable paradigm for high‐performance, low‐cost, and compact THz wave plates.