Broadband Absorption and Switchable Multiband Polarization Conversion via Graphene-VO₂ Metasurface

We demonstrate the broadband absorption and multiband switchable polarization conversions through a cascaded metasurface consisting of periodic gold split-ring resonator formed of two L-shaped patterns and metal square ring based on graphene and vanadium dioxide (VO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>). More concretely, the metasurface is able to capture electromagnetic fields with a relative bandwidth of 116% and an absorption rate of more than 90% when graphene is applied with Fermi level of 0 eV and VO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is in the conducting state. On the other hand, when we set the VO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> in the insulating state and the Fermi level of graphene is set to 0 eV, the structure enables broadband linear-to-linear polarization conversion with an efficiency greater than 90% over a relative bandwidth of 74.8%. Notably, when the Fermi level is adjusted to 1 eV, the structure functions as a multi-band linear-to-circular polarization converter. This design extends the function of polarization conversions without reducing the absorption bandwidth, should pave the way for more advanced manipulations of electromagnetic fields.