Fano-resonance-based mode-matching hybrid metasurface for enhanced second-harmonic generation.

Plasmonic nanostructures have been considered as potential candidates for enhancing the nonlinear upconversion rate at nanoscale levels due to their strong near-field enhancement. Here, we propose a Fano-resonance-based mode-matching hybrid metasurface that combines the advantages of Fano resonances and mode-matching for boosting second-harmonic conversion. A confined and strong near-field intensity is generated by gold nanoantennas within the volume of polycrystalline zinc sulfide nanoparticles, thus resulting in a larger effective second-harmonic coefficient. The combination of the abovementioned features allows for the realization of a second-harmonic generation (SHG) conversion efficiency of 5.55×10-8, and the SHG signal is twice that obtained with dipole hybrid metasurfaces. Our designed metasurface may pave the way for optimizing nonlinear light-matter interactions at the nanoscale.