Ultrathin planar chiral metasurface for controlling gradient phase discontinuities of circularly polarized waves

We develop a gradient phase discontinuities ultrathin planar metasurface based on chiral branched gammadion structure (CBGS) that provides extreme control of electromagnetic wavefronts across single-sheet design. The introduction of the branch can provide antiparallel magnetic moment, which tunes the chirality of the CBGS. In the CBGS metasurface, the transmission phase of a circularly polarized wave can be varied from -180° to +180°. We experimentally demonstrate a beam-refracting CBGS metasurface with refracting a normally incident plane wave to an angle of 17°. The performances of the proposed metasurface at oblique incidence are also presented. The CBGS metasurface can find a wide range of applications over the entire electromagnetic spectrum including single-surface lenses, fully controlling light in direction, and polarization controlling devices.