Janus Reflective Polarization-Division Metadevices With Versatile Functions

A novel concept of Janus polarization multiplexed circularly polarized (CP) metadevices is proposed to afford an alternative avenue toward versatility and capacity limit of integrated functions. Six polarization-division channels are engineered by synergizing space division and polarization division based on developed generalized spin-decoupling theory involving both geometric and dynamic phases. By combining and stimulating two polarization-division compound metasurfaces at both sides, four or six co/cross-CP channels are facilitated at $X$ and Ku bands in full space. The compound meta-atom is composed of two anisotropic birefringent sub-meta-atoms sharing the same ground. Due to the shielding effect of the medium ground, the resulting functions generated in front and back channels are inherently insulated and thus can be engineered individually and completely different. For demonstration and possible applications, two proof-of-concept metadevices are designed: one is a Janus steering-beam generator with four predesigned uniform-intensity CP beams in the front and back cross-CP channels; the other is a compound metadevice capable of forwardly generating nondiffractive propagation with three diversified foci in four full CP channels while backwardly integrating radar cross section (RCS) reduction and quad-vortex-beam generation of multiple topological charges at two cross-CP channels. For experimental verification, the compound metadevice was fabricated, and numerical and experimental results coincide well and manifest high efficiency, illustrating the effectiveness of space-polarization multiplexing concept in engineering versatile energy distribution adaptive to environment.