Broadband Independent Absorption Control for Orthogonal Circular Polarized Waves Using Achiral Active Metasurface

Chiral structures have attracted the interests of a large number of researchers in biological, optical and electromagnetic area. Due to their diverse abilities to manipulate circularly polarized (CP) waves, many novel electromagnetic effects can be generated, such as circular dichroism (CD), which means the absorption of only one helicity of the two circular polarizations. Various structures have been designed to tune the CD effects through varying structural parameters. However, the traditional chiral structures only response to one circularly polarization, and the passive materials cannot be controlled dynamically. In this paper, we introduced an active achiral metasurface design that enables independently control the absorption for the two orthogonal CP waves in the microwave frequencies with a broadband working performance. The design is a typical metal-dielectric-metal sandwich structure with a C-shaped splitted ring resonator on the top layer, where two PIN diodes are inserted into the two arms at the two sides to independently control the reflection of left circularly polarized (LCP) and right circularly polarized (RCP) incident waves. Through loading different biasing voltages on the two PIN diodes, four working states can be dynamically switched: circular polarization conversion with no absorption, CD absorption for RCP, CD absorption for LCP and absorption for all polarizations. Particularly, the absorption efficiencies depend on the resistance values of the PIN diodes which can be manipulated by changing the biasing voltages. To sum up, the absorption for RCP and LCP waves can be independently controlled with an active method, which is suitable to various absorption application scenarios. We are convinced that our design methodology can be extended to other frequency regimes and achieve more diversified optical, terahertz or electromagnetic applications in the further.