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

Polarization plays a key role in fundamental science, and manipulating the evolutionary trends of longitudinal polarization states can provide new implements for light-matter interaction. However, existing 3D optical devices can only manipulate the polarization conversion in a single transverse plane. Recently, methods to control polarization by cascading bulky optical systems are miniaturized using metasurfaces. Nevertheless, it is quite challenging to generate focused beams with vectorial properties for metasurfaces carrying inhomogeneous polarization profiles. Here, a single-layer all-silicon metasurface operating in the terahertz (THz) band is demonstrated to address all those aforementioned challenges in one go, and pencil-like beams with inhomogeneous polarization profiles can be imparted along the propagation direction. The introduction of a latitudinal polarization control factor representing the initial phase difference enables near-even manipulation of the evolutionary trend of the longitudinal polarization state according to the extended focal depth. By manipulating the topological charges within two orthogonal circularly polarized channels to accomplish coherent superposition, a focused vortex beam with vectorial properties can be generated in desired planes. Two functional demonstrations based on this approach are established experimentally, offering promising opportunities for structured light on meta-optics.

Automated summary

This paper introduces a single-layer all-silicon metasurface operating in the terahertz band, which can address the challenges of manipulating polarization conversion and generate focused beams with inhomogeneous polarization profiles.