Exceptional points with opposite chirality from metasurface enantiomers and application in dual phase-encoding...

Recently. the topological properties of exceptional points (EPs) in non-Hermitian metasurfaces have been employed in optical phase engineering, which is mainly due to the rigorous 2π-phase accumulation around a single EP. Thus far, the great majority of research has been done on a single isolated EP, due to more than one EP not being easily attainable in such resonance-induced loss systems. In this work, we have found that for the Ag non-Hermitian metasurfaces, the oppositely chiral EPs exist respectively in the mirror-symmetric metasurface enantiomers, and the 2π topological phase was achieved surrounding each one in different positions in the parameter space. By utilizing the two EPs with opposite chirality, a dual phase-encoding hologram is proposed, in which two kinds of phases can be endowed to a metasurface, producing two different holographic images under illumination of oppositely circularly polarized light.