Direction-Duplex Janus Metasurface for Full-Space Electromagnetic Wave Manipulation and Holography

Janus metasurfaces, a category of two-faced two-dimensional(2D)materials, are emerging as a promising platform for designing multifunctionalmetasurfaces by exploring the intrinsic propagation direction (k-direction) of electromagnetic waves. Their out-of-planeasymmetry is utilized for achieving distinct functions selectivelyexcited by choosing the propagation directions, providing an effectivestrategy to meet the growing demand for the integration of more functionalitiesinto a single optoelectronic device. Here, we propose the conceptof direction-duplex Janus metasurface for full-space wave controlyielding drastically different transmission and reflection wavefrontsfor the same polarized incidence with opposite k-directions.A series of Janus metasurface devices that enable asymmetric full-spacewave manipulations, such as integrated metalens, beam generators,and fully direction-duplex meta-holography, are experimentally demonstrated.We envision the Janus metasurface platform proposed here to open newpossibilities toward a broader exploration of creating sophisticatedmultifunctional meta-devices ranging from microwaves to optical systems.