Chirality-Intrigged Spin-Selective Metasurface and Applications in Generating Orbital Angular Momentum

Spin-selective metamirrors consisting of planar meta-atoms are able to reflect tailored incident circularly polarized (CP) waves either in similar or opposite handedness while absorbing the other handedness of spin-wave. In this article, we propose a novel design of a metamirror exhibiting both spin-selective absorption and phase modulation properties. A chiral metamirror with asymmetric split-ring resonators (ASRRs) is proposed to achieve spin-selective reflection/absorption. Meanwhile, a geometric phase is introduced to provide a full $2\pi $ reflection-phase coverage. Theoretical results indicate a maximum absorption of 99.34% for left-handed circularly polarized (LHCP) wave, while keeping the reflection of right-handed circularly polarized (RHCP) higher than 91% without changing the handedness. By virtue of the above merits, we implement a metadevice that can convert incident RHCP waves into vortex waves with identical handedness from 8.3 to 10.3 GHz and absorb incident LHCP waves at its operation band. For experimental verification, a proof-of-concept metamirror is fabricated and experimentally characterized, which reveals the spin-dependent bifunctional performances of the proposed metamirror. Our strategy provides a promising route for the realization of spin-selective planar devices in wireless communications.