Spin-decoupled amplitude and phase control by chiral metasurfaces for four-channel focusing

Abstract The spin-decoupled phase modulation by metasurfaces mainly depended on a combination of the propagation phase and the Pancharatnam–Berry phase, and there was few research on the phase modulation by a single approach. In this paper, we propose an amplitude-phase joint modulation method via L-shaped enantiomers of the two-dimensional (2D) chiral geometry feature by numerical simulations. By adjusting the top and bottom arm of the 2D L-shape meta-atom, independent modulations on both the spin-related amplitude and phase can be obtained. Consequently, as a proof-of-concept demonstration, the spin-selective focusing effect in both transmission and reflection channels are achieved by a typical L-enantiomer metalens. The proposed amplitude-phase joint modulation method, feasibly achieved by tailoring the enantiomer geometry of 2D chiral nano-structures, provides a new approach for the modulation of circularly polarized light and has potential applications in high-performance spin-photonic devices, including polarimetric imaging and chiral bioimaging.