Fig. 4

Nonlinear-optically tunable metasurfaces. a Plasmonic-antenna assisted tunable meta-atom by Kerr nonlinearity [69]. Reproduced with permission from ©2013, Springer Nature. b Optical pumping leads to Fabry-Pérot resonance shift owing to the large nonlinearity of a nanocavity [70]. Reproduced with permission from ©2018, American Chemical Society. c Polarization converter based on molecular transformation [71]. Reproduced with permission from ©2017, Springer Nature. d Fifth harmonic generation from a hybrid oxide heterostructure near ENZ condition [72]. Reproduced with permission from ©2019, Springer Nature