Near-unity third-harmonic circular dichroism driven by quasi-BIC in asymmetric silicon metasurfaces

TL;DR

This paper demonstrates near-unity third-harmonic circular dichroism and high conversion efficiency in asymmetric silicon metasurfaces, enabled by quasi-bound states in the continuum, advancing nonlinear chiro-optical device development.

Contribution

It introduces a method to achieve near-unity nonlinear circular dichroism in silicon metasurfaces by exploiting quasi-bound states in the continuum with tunable multi-mode interference.

Findings

Achieved high third-harmonic circular dichroism (>99%)

Demonstrated high conversion efficiency ($10^{-2}\, ext{W}^{-2}$)

Controlled linear and nonlinear CD independently

Abstract

We use numerical simulations to demonstrate third-harmonic generation with near-unity nonlinear circular dichroism (CD) and high conversion efficiency ($ 10^{-2}\ \text{W}^{-2}$) in asymmetric Si-on-SiO$_2$ metasurfaces. The working principle relies on the selective excitation of a quasi-bound state in the continuum, characterized by a very high ($>10^5$) quality-factor. By tuning multi-mode interference with the variation of the metasurface geometrical parameters, we show the possibility of independent control of linear CD and nonlinear CD. Our results pave the way for the development of all-dielectric metasurfaces for nonlinear chiro-optical devices with high conversion efficiency.