Enhanced Second-Harmonic Generation by Metasurface Nanomixer and Nanocavity

We discuss the possibility of largely enhancing the nonlinear second-harmonic generation (SHG) from chi((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 chi((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.