Fig. 1. Nonlinear metasurfaces for second-harmonic generation. (a) Several metallic metasurfaces based on different structures; (b) TiN plasmonic metasurface with high damage threshold; (c) GaAs metasurface supporting Mie resonance; (d) GaAs metasurface supporting Fano resonance; (e) AlGaAs metasurface supporting BIC mode; (f) Multi-quantum-well metasurface with plasmon coupled to intersubband transitions; (g) Silicon metasurface with electric-field-induced-second-harmonic-generation

Fig. 2. Nonlinear metasurfaces for third-harmonic generation. (a) Several metallic metasurfaces based on different structures; (b) Silicon metasurface supporting Mie resonance；(c) Silicon metasurface supporting Fano resonance; (d) Silicon metasurface supporting anapole mode; (e) Silicon metasurface supporting BIC mode

Fig. 3. Nonlinear metasurfaces for high-harmonic generation. (a) Gaseous high harmonic sources with near-field enhancement based on a metallic metasurface; (b) Plasmon-enhanced metal-sapphire metasurface; (c) Plasmon-enhanced hybrid metal-silicon metasurface; (d) Silicon metasurface supporting Fano resonance; (e) GaAs metasurface supporting magnetic-dipole resonance

Fig. 4. Broadband terahertz wave generation based on a nonlinear metallic metasurface

Fig. 5. Nonlinear metasurfaces for wavefront control. (a) Using nonlinear geometric phase to achieve deflection of different orders of harmonics; (b) Using nonlinear propagation phase to achieve deflection and vortex light generation of third-harmonic signal; (c) Holograms of the fundamental frequency and the different chirality-dependent second-harmonics based on a metallic metasurface; (d) Holograms of orthogonal polarization based on a metallic metasurface; (e) Third-harmonic holograms based on a silicon metasurface; (f) Optical vortices of second-harmonics based on a metallic metasurface; (g) Polarization manipulation of second-harmonics based on a metallic metasurface

Fig. 6. Nonlinear metasurfaces for ultrafast control. (a) All-optical control based on a silicon metasurface ; (b) All-optical control based on a metallic metasurface; (c) Metallic metasurface with the relaxation channel of ITO; (d) Strong-coupled metasurface combined with metal and ITO; (e) Laser Q-switching and mode-locking with metallic metasurface as a saturable absorber