Full-Phase Modulated Chiral Metalens for Subwavelength-Resolution Terahertz Holography

Chiral metasurface is an important platform for engineering circular dichroism and optical activity. Thanks to the unprecedented capabilities of optical metasurfaces for light-field control, metalenses enable the achievement of various desired functions. In this paper, we propose and experimentally demonstrate a chiral metalens based on a full-phase modulated approach to realize subwavelength-resolution terahertz holography. The all-dielectric chiral metalens is composed of metamolecules consisting of two different sub-meta-atoms. Destructive and constructive interference are induced through phase control of the transmission amplitude and phase of two sub-meta-atoms under the incidence of orthogonal circularly polarized light beams, resulting in a considerable chiral effect. To achieve terahertz wavefront shaping, the geometric phase is introduced by rotating the azimuth angle of the sub-meta-atoms with the interference effect. Each focal point of the chiral metalens was employed as an individual hologram pixel, enabling subwavelength resolution in the chiral terahertz hologram. By independently controlling the position of each focal point, we successfully demonstrated chiral holographic imagery ranging from 2D to 3D patterns. Owing to its flexible design and ultrathin architecture, the chiral metalens holds great potential for integrated photonic systems, particularly in chiroptical spectroscopy, chiral imaging, and terahertz communications.