Full Poincaré sphere vectorial polarization transformation of terahertz wave based on chiral metasurfaces

Metasurfaces exhibit significant advantages in the vectorial polarization manipulation of light beams, owing to their precision and multi-dimensional wave control capabilities in subwavelength-scale. However, metasurfaces for arbitrary vectorial polarization transformation still remains challenging. Here, we propose a chiral metasurface platform for arbitrary vectorial polarization transformation of transmitted terahertz beams, with obtainable polarization states nearly covering the entire Poincaré sphere. We fully exploit the mirror symmetry breaking, geometric parameter space evolution, in-plane rotation, and mirror-flip operations of the dielectric meta-atoms to comprehensively expand the polarization states. We analyze the influence caused by intrinsic properties of meta-atoms on the polarization states using Jones matrix theory, from the perspective of linear polarization bases. Then, two metasurfaces are demonstrated to illustrate a direct generation method for vectorial terahertz beams. Additionally, from the perspective of circular polarization bases, the possibility of achieving joint control of scalar polarization states and wavefronts with the scheme is clarified, then a sample is designed, fabricated, and experimentally validated. The above results confirm the feasibility of arbitrary vectorial polarization transformations using chiral metasurfaces, providing new insights for high-efficiency and multi-dimensional manipulation of light or terahertz waves.