Enhanced third-harmonic generation and degenerate four-wave mixing in an all-dielectric metasurfaces via Brillouin zone folding-induced bound states in the continuum

TL;DR

This paper demonstrates significant enhancement of third-harmonic generation and four-wave mixing in all-dielectric metasurfaces by utilizing Brillouin zone folding-induced bound states in the continuum, enabling efficient nonlinear optical responses.

Contribution

The study introduces a novel approach using BZF-BICs in nonlinear metasurfaces to substantially boost third-order nonlinear optical processes.

Findings

Enhanced THG and dFWM achieved in metasurfaces

BZF-BICs provide the strongest nonlinear enhancement

Simulated output powers reach 10^{-4} W (THG) and 10^{-2} W (dFWM)

Abstract

Bound states in the continuum (BICs) exhibit significant electric field confinement capabilities and have recently been employed to enhance nonlinear optics response at the nanoscale. In this study, we achieve substantial enhancement of third-harmonic generation (THG) and degenerate four-wave mixing (dFWM) by implementing Brillouin zone folding-induced BICs (BZF-BICs) in an air-hole type nonlinear metasurface. By introducing gap perturbations within the metasurface, guided modes below the light line can be folded into the light cone, resulting in three resonant modes: guided resonances (GRs), $\Gamma$-BICs, and BZF-BICs. Through the eigenvalue analysis and multipole decompositions, we establish their excitation conditions. With their resonantly enhanced local field, we successfully boost both THG and dFWM under $x$- and $y$- polarizations within the same metasurfaces. The simulated results indicate that the BZF-BICs provide the most significant enhancement of third-order nonlinear optical responses, with the output power of THG to 10$^{-4}$ W and dFWM output power of 10$^{-2}$ W under a moderate input power density of 1 MW/cm$^{2}$. These findings demonstrate that the BZF-BICs can offer an effective pathway for chip-scale nonlinear optical applications.