Efficiency adjustable terahertz circular polarization anomalous refraction and planar focusing based on a bi-layered complementary Z-shaped graphene metasurface

Abstract

Metasurfaces (MSs) have received great attention due to their wide application potentials in terahertz (THz) wavefront manipulation. Although great achievements have been obtained in MSs so far, the functionalities are almost static. The active adjustable MS-based devices are far less explored. In this paper, an efficiency adjustable MS composed of a dielectric substrate sandwiched with bi-layered complementary Z-shaped (CZS) structure graphene is proposed and investigated theoretically, which can control the THz circular polarization (CP) wavefront in transmission mode. The simulation results show that the MS structure under a Fermi energy level of 1.0 eV can realize CP conversion with efficiency of about 0.9, and the full range of a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>2</mml:mn> </mml:mrow> </mml:mrow> <mml:mi>π</mml:mi> </mml:math> phase shift also can be achieved by changing the rotation angle of the CZS structure graphene along the wave propagation direction. More importantly, the transmission CP conversion efficiency is positively correlated with the Fermi energy levels of graphene. The anomalous refraction and planar focusing effect can be realized by the specific design of a spatial phase profile of the graphene MS, and the corresponding efficiencies can be adjusted by changing the Fermi energy level of the graphene. Adjustable graphene MSs have wide application prospects in the fields of communication, imaging, and other THz wavefront manipulation devices.