Realization of Spatiotemporal Photonic Crystals Based on Active Metasurface

Spatiotemporal photonic crystals (STCs) are artificial materials with tunable nonresonant wave amplification in the subwavelength scale, which is induced by the intrinsic mixed gap equipped with a complex Bloch wavenumber and a complex Floquet frequency, paving a new way in light amplification. In this work, the concept of STCs is extended to an active electrically controlled spatiotemporal metasurfaces. It is demonstrated that the spatiotemporal metasurface completely inherits the critical mixed momentum-energy gap of STCs, dictated by the interplay between the temporal modulation with exponential growth and spatial modulation with the exponential decay. Based on the design of spatiotemporal metasurfaces, the possibility of accurately manipulating the mixed bandgap related to surface waves is experimentally confirmed through time modulation, as well as the variability of the transmission properties of electromagnetic waves at the interface.