Space and Time Modulations of Light with Metasurfaces: Recent Progress and Future Prospects

In this Perspective, we discuss the different opportunities offered by time-modulated metasurfaces for dynamic wavefront engineering and space-time photonics. Efforts in codesigning a photonic response while taking into careful consideration the switching/tuning mechanisms, including thermal, electronic, optical, chemical, and mechanical actuation, are essential for achieving sufficient amplitude, phase, and polarization modulation. Here, we examine in detail how the key enabling photonic technologies currently available and relying on similar tuning mechanisms can be applied for the conception of tunable metasurfaces. We review the latest developments and discuss the advantages and limitations of each approach, providing the reader with a clear vision of the current state of the art in active metasurfaces. We also address the readiness of each technological approach to drawing short- and long-term application perspectives. Finally, we discuss perspectives for spatiotemporal metasurface modulation opening new horizons toward unlimited wavefront engineering capabilities.