Manipulation of Longitudinally Inhomogeneous Polarization States Empowered by All-Silicon Metasurfaces

摘要

Polarization plays a key role in fundamental science, and manipulating theevolutionary trends of longitudinal polarization states can provide new implementsfor light–matter interaction. However, existing 3D optical devices canonly manipulate the polarization conversion in a single transverse plane.Recently, methods to control polarization by cascading bulky optical systemsare miniaturized using metasurfaces. Nevertheless, it is quite challenging togenerate focused beams with vectorial properties for metasurfaces carryinginhomogeneous polarization profiles. Here, a single-layer all-silicon metasurfaceoperating in the terahertz (THz) band is demonstrated to address allthose aforementioned challenges in one go, and pencil-like beams with inhomogeneouspolarization profiles can be imparted along the propagation direction.The introduction of a latitudinal polarization control factor representingthe initial phase difference enables near-even manipulation of the evolutionarytrend of the longitudinal polarization state according to the extendedfocal depth. By manipulating the topological charges within two orthogonalcircularly polarized channels to accomplish coherent superposition, a focusedvortex beam with vectorial properties can be generated in desired planes. Twofunctional demonstrations based on this approach are established experimentally,offering promising opportunities for structured light on meta-optics.