Metasurface with Nanostructured Ge₂Sb₂Te₅ as a Platform for Broadband‐Operating Wavefront Switch

Abstract Broadband‐operating active devices within a small‐footprint are highly on demand in various nanophotonic fields such as fiber‐optic communication systems and chip‐based integrated optical circuits. As pioneering approaches, diverse platforms of active metasurfaces (AMs) have been proposed due to their superior tunable functionality and ultra‐compact size. However, most of previous researches provide only limited operating bandwidth because they generally rely on resonant light–matter interaction between active material and plasmonic antenna. In this study, an active wavefront switching metasurface that can operate over 500 nm bandwidth at near‐infrared spectral bands is experimentally realized by utilizing nonresonant U‐shaped Ge₂Sb₂Te₅ nanoantennas. Two different sizes of the U‐shaped antenna are designed to exhibit large transmittance contrast and their optical phases are determined by imposing the orientation angle variation. As an example of the functionality, anomalous refraction angle switching and dispersionless active hologram are demonstrated. The devices provide high signal‐to‐noise ratio (>7 dB) for overall operation bandwidth. It is believed that the proposed AMs can be an innovative platform for real device application thanks to their not only broadband and low‐noise operation but also fast speed, low power consumption switching within a small‐footprint.