Independent control of circularly polarized light with exceptional topological phase coding metasurfaces

Exceptional points,as degenerate points of non-Hermitian parity-time symmetric systems,have many unique physical properties.Due to its flexible control of electromagnetic waves,a metasurface is frequently used in the field of nanophotonics.In this work,we developed a parity-time symmetric metasurface and implemented the 2πtopological phase surrounding an exceptional point.Compared with Pancharatnam-Berry phase,the topological phase around an exceptional point can achieve independent regulation of several circular polarization beams.We combined the Pancharatnam-Berry phase with the exceptional topological phase and proposed a composite coding metasurface to achieve reflection decoupling of different circular polarizations.This work provides a design idea for polarimetric coding metasurfaces in the future.