Experimental demonstration of resonant third-harmonic generation using quasi-BIC resonances in silicon elliptical dimer metasurfaces with nanodisk couplers

Design and experimental demonstration of resonant two-dimensional amorphous silicon (a-Si) metasurface supporting mid-infrared quasi-BIC resonances and its application for resonant third harmonic generation enhancement are discussed. Symmetry-protected bound-state-in-continuum resonance is made accessible with the addition of nanodisk couplers in between elliptical dimers with a vertical offset in the symmetry plane. Fabricated quasi-BIC resonant structures show a clear transmission resonance peak at 2470 nm wavelength with a Q-factor of 80. Third-harmonic generation (THG) based up-conversion from 2470 nm fundamental excitation to 823 nm THG shows resonant THG enhancement by 35 times for TM polarized excitation with strong polarization dependence.