Dual-encryption freedom via a monolayer-nanotextured Janus metasurface in the broadband visible.

As an emerging category of two-faced 2D architecture, the Janus metasurface aims to explore another universal optical property, that is, the wavevector direction (k-direction), and to enable the asymmetric transmission between the opposite directional incidences. It exhibits significant potential in creating versatile multiplexing metasurfaces and an optical isolator in optical communication applications. However, most previous asymmetric functionality shows merely one-way functionality with the other-way simply muted or demands multilayered nanostructure fabrication and alignment. Hence, it remains a great challenge to make a monolayer-nanotextured Janus metasurface with dual-encryption freedom and conquering the difficulty for multilayer alignment and practical operation bandwidth. In this work, we have proposed and experimentally demonstrated a new strategy of a dual-encryption Janus metasurface design with a simple monolayer-nanotextured metasurface coupled with a commercialized film of the half-wave plate. Utilizing the hybridization from two independent geometrical dimensions of rectangular-antennas, our approach ingeniously transforms the polarization-multiplexing into the dual-directional channels. A series of calculations and experimental results demonstrate that our asymmetric approach simultaneously constructs completely independent imaging encryptions for both forward and backward directions. Additionally, our proposed approach becomes a practical scheme with broadband visible-frequency operation and great simplicity in design and nanofabrication. We believe the universal scheme could facilitate to increase the information encoding capacity and holographic multiplexing channels by expanding the illumination wavevector to the full-space (+/-), and it paves the route toward the potential applications in on-chip integration, telecommunications, encryption, information processing, and communication.