Robust enhancement of high-harmonic generation from all-dielectric metasurfaces enabled by polarization-insensitive bound states in the continuum

Abstract

The emerging all-dielectric platform exhibits high-quality (Q) resonances governed by the physics of bound states in the continuum (BIC) that drives highly efficient nonlinear optical processes. Here we demonstrate the robust enhancement of third-(THG) and fifth-harmonic generation (FHG) from all-dielectric metasurfaces composed of four silicon nanodisks. Through the symmetry breaking, the genuine BIC transforms into the high-Q quasi-BIC resonance with tight field confinement for record high THG efficiency of 3.9 × 10^-4 W^-2 and FHG efficiency of 4.8 × 10^-10 W^-4 using a moderate pump intensity of 1 GW/cm². Moreover, the quasi-BIC and the resonantly enhanced harmonics exhibit polarization-insensitive characteristics due to the special C₄ arrangement of meta-atoms. Our results suggest the way for smart design of efficient and robust nonlinear nanophotonic devices.