Spin-multiplexed phase and amplitude manipulations of terahertz waves based on chiral metasurfaces.

The independent manipulation of circularly polarized electromagnetic waves is a significant topic in the field of micro-nano optics, and metasurfaces provide a convenient solution for this target. However, the design of metasurfaces is still complex, often involving both parameter space and polarization space, where the simultaneous control of amplitude and phase is quite challenging. In this paper, we propose a new scheme for the spin-multiplexed control of amplitude and phase based on chiral metasurfaces, which only consider the parameter space. By sequentially breaking the in-plane mirror symmetry and second-order rotational symmetry of meta-atoms, we demonstrate two types of metasurfaces in the terahertz band. The first one achieves spin-multiplexed phase control of co-polarized terahertz waves solely through a chiral phase, with a reflection efficiency greater than 71.7% for both components. The other one is demonstrated for the joint control of phase and amplitude of the reflected circularly polarized wave. To validate the effectiveness of the scheme, two devices were designed with wavefront profiles such as focusing and deflection for functional verification. The results illustrate that by exploring and designing the parameter space of chiral meta-atoms, we can independently control circularly polarized waves using a chiral phase and circular dichroism, thus providing a new method for designing metasurfaces for spin-multiplexed amplitude-phase manipulations.