Linear‐Polarization‐Preserving Metasurfaces Based on Identically Spin‐Locked Geometric Phase

Abstract

Metasurfaces have provided unprecedented degrees of freedom in controlling electromagnetic waves. By introducing geometric phase into metasurface, remarkable progresses have been made in manipulation circular polarized(CP) waves. However, for linearly polarized (LP) waves, polarization purity has to be sacrificed for wideband phase responses. Thus, it is desirable that wideband metasurfaces be explored for LP waves without polarization conversion. Herein, they propose a strategy of achieving wideband linear‐polarization‐preserving (LPP) metasurfaces based on identically‐spin‐locked (ISL) geometric phases. Different from the rotation‐induced oppositely‐spin‐locked (OSL) geometric phase (φL = −φR), the ISL geometric phase is the same for left‐ and right‐handed circularly polarization (LCP&RCP) states (φL = φR). Since LP waves can be decomposed into LCP and RCP waves, the same phase can also be imparted to LP waves, without changing the polarization. Therefore, wideband LPP metasurfaces can be designed. As the proof‐of‐concept, the quadru‐arc structure (QAS) is proposed to construct the LPP metasurfaces. Two prototypes, one for vortex beam generation and the other for deflection‐absorption integration, are implemented. Both the simulated and measured results verify the LPP in wideband. This work opens a wideband gate towards wideband manipulation on LP waves and can be readily extended to higher frequency bands such as terahertz, infrared and optical regimes.