We study, both theoretically and experimentally, tunable metasurfaces supporting sharp Fano-resonances inspired by optical bound states in the continuum. We explore the use of arsenic trisulfide (a photosensitive chalcogenide glass) having optical properties which can be finely tuned by light absorption at the post-fabrication stage. We select the resonant wavelength of the metasurface corresponding to the energy below the arsenic trisulfide bandgap, and experimentally control the resonance spectral position via exposure to the light of energies above the bandgap.

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.

Metasurfaces and, in particular, metalenses have attracted large interest and enabled various applications in the near-infrared and THz regions of the spectrum. However, the metalens design in the visible range stays quite challenging due to the smaller nanostructuring scale and the limited choice of lossless CMOS-compatible materials. We develop a simple yet efficient design of a polarization-independent, broadband metalens suitable for many CMOS-compatible fabrication techniques and materials and implement it for the visible spectral range using niobium pentoxide (Nb2O5). The produced metalens demonstrates high transmittance and focusing ability as well as a large depth of focus, which makes it a promising solution for a new generation of silicon photomultiplier photodetectors with reduced fill factor impact on the performance and reduced electron–hole generation regions, which altogether potentially leads to improved photodetection efficiency and other characteristics.