Enhanced Second-Harmonic Generation by Metasurface Nanomixer and Nanocavity

We discuss the possibility of largely enhancing the nonlinear second-harmonic generation (SHG) from Ξ⁽²⁾ nonlinear materials using metasurfaces consisting of suitably engineered optical nanoantenna arrays. The proposed setup may increase the SHG conversion efficiency by orders of magnitude, compared to a thin film of Ξ⁽²⁾ nonlinear material of the same thickness. This enhancement is attributed to localized fields at the nanoload, due to the plasmonic resonance of noble-metal nanoantennas, combined with a suitably enhanced photonic local density of states induced by properly coupling two closely spaced metasurfaces to form a nanocavity to enhance SHG. The proposed subwavelength optical device can lead to versatile applications, such as wavelength conversion and wave mixing at the nanoscale.