Introduction of non-symmetric inserts into a symmetric split-ring resonator: design of a bifunctional metasurface for linear polarization conversion and circular dichroism

Metasurfaces have shown their versatile capabilities in light-field shaping. To further pursue dense integration and miniaturization in photonics, a combination of multiple diversified functionalities into a metasurface is a promising solution. Recent bifunctional metasurfaces have relied on meta-atom superposition and tunable material introduction. The former supports simultaneous multi-functions, while the latter provides flexible adjustment. To achieve simultaneous and tunable multi-functions using a simple structure, based on a split-ring resonator metasurface with the linear polarization modulation function, here, we additionally introduced resonance to induce anti-symmetric polarization absorption for circular polarization modulation. As a proof-of-concept, we propose a bifunctional THz metasurface that combines linear polarization conversion and circular dichroism for polarization control and detection applications. Moreover, by changing the Fermi levels of graphene, both the frequency ranges of linear polarization conversion and circular dichroism can be adjusted. This work provides a reference to photonics integration related to polarization engineering and other distinct functionalities.