Chirality-Assisted Phase Metasurface for Circular Polarization Preservation and Independent Hologram Imaging in Microwave Region

A chirality-assisted phase is introduced to innovatively impose separate phase profiles in two circular polarization (CP) preserving channels, namely, two co-polarized output components under left-handed and right-handed circularly polarized (LHCP and RHCP) illuminations. Such a scheme is physically implemented by a proposed multi-layered meta-atom that achieves chiral characteristics by inner twisting angles between adjacent functional elements. A proof-of-concept metasurface is constructed to realize separate holographic images in two polarization-preserved fields with different propagating distances, respectively. In order to achieve sufficient utilization of the two polarization-preserved components, a further approach that can suppress polarization conversion is proposed with a polyatomic unit composed of four separate chiral meta-atoms arranged in a $2\times $ 2 array. A dual-holographic metasurface is designed to impose characters " $L$ " and " $R$ " in two co-polarized fields with little energy distributed in corresponding cross-polarized fields. A prototype of the metasurface is fabricated and experimentally measured. The measurements agree well with theoretical predictions and full-wave simulations, showing in the co-polarized field a character " $L$ " under LHCP incidence and an " $R$ " under LHCP incidence. The proposed mechanism provides a theoretical foundation for further CP channel expansion and modulations and has great potential in multifunctional antenna design and wireless communications.