Nonvolatile Switchable Janus Metasurface for Multi‐Dimension Encoded Near‐ And Far‐Field Functionalization

Abstract Through considering an unconventional parameter of electromagnetic waves, Janus metasurfaces offer a new strategy to integrate multiple functionalities into a single device. However, the traditional Janus metasurfaces lack reconfigurability and suffer from complex manufacture process due to common multilayer structures. Herein, it is shown that a multi‐encrypted Janus metasurface integrating with phase change material Ge 2 Sb 2 Te 5 (GST) can achieve tunable switching of dual functionalities and two‐faced spatial asymmetric wavefront manipulation. By controlling four degrees of freedom (i.e., incident wavelength, polarization, output direction, and the phase state of GST), the metasurfaces can simultaneously enable transmitted phase and reflected amplitude modulations. As an experimental demonstration, a transmission‐type hologram and a reflection‐type grayscale image are securely encrypted in a single metasurface and actively switched with two specific keys, which contains four optical parameters. The nonvolatile switchable Janus metasurfaces provide potential applications in displays, information encryption, and data storage.