Stereo Metasurfaces for Efficient and Broadband Terahertz Polarization Conversion

Efficient and flexible manipulation of terahertz (THz) polarization in a broadband manner using metasurfaces has attracted continuous attention in recent years. Previous studies have commonly applied multilayer metallic resonators or bonded dielectric structures as the basic units, which are affected by the spacer loss or bonding difficulty and stability. Here, a new design scheme is proposed based on an all-metal stereo U-shaped meta-atom working in a reflection configuration. The stereo metasurface functions as an efficient and broadband THz waveplate with tailorable birefringence simply controlled by the sunken depth. Such an intriguing property is experimentally verified by a reflection-type THz half-waveplate. The polarization conversion ratio is higher than 90%, with 69% relative bandwidth and over 85 degrees angle tolerance for incidence. Furthermore, an efficient and broadband meta-grating based on the Pancharatnam-Berry phase method is also experimentally demonstrated. The proposed strategy enriches the design degrees of freedom of polarization-related metasurfaces and may find broad applications in realizing various functional devices.