All-dielectric χ<sup>(2)</sup> metasurfaces: recent progress

Optical metasurfaces, i.e. arrays of nanoantennas with sub-wavelength size and separation, enable the manipulation light-matter interactions in miniaturized optical components no classical counterparts. Six decades after first observation second harmonic generation (SHG) bulk crystals, these devices are expected to break new ground field nonlinear optics, shifting focus from phase matching approach achieved within long propagation distances that near-field resonances interplay leaky nanocavities. Here we review recent progress SHG all-dielectric metasurfaces. We discuss most used technological platforms which underpinned such advances analyze different control approaches. finally compare their performances other well-established technologies, hope delineate current state-of-the-art figure out a few scenarios might soon offer unprecedented opportunities.