High-Q Resonances Governed by the Quasi-Bound States in the Continuum in All-Dielectric Metasurfaces

TL;DR

This paper demonstrates how symmetry-protected bound states in the continuum enable high-Q resonances in all-dielectric metasurfaces, significantly enhancing nonlinear optical effects like third harmonic generation.

Contribution

It introduces a tunable approach to achieve ultrasharp resonances in silicon metasurfaces by manipulating BICs and structural parameters, advancing metasurface design.

Findings

Q factor exceeds 3000 through structural optimization

Third harmonic generation signal is 368 times stronger than flat silicon

Resonance properties can be tuned via topological BIC configurations

Abstract

The realization of high-Q resonances in a silicon metasurface with various broken-symmetry blocks is reported. Theoretical analysis reveals that the sharp resonances in the metasurfaces originate from symmetry-protected bound states in the continuum (BIC) and the magnetic dipole dominates these peculiar states. A smaller size of the defect in the broken-symmetry block gives rise to the resonance with a larger Q factor. Importantly, this relationship can be tuned by changing the structural parameter, resulting from the modulation of the topological configuration of BICs. Consequently, a Q factor of more than 3,000 can be easily achieved by optimizing dimensions of the nanostructure. At this sharp resonance, the intensity of the third harmonic generation signal in the patterned structure can be 368 times larger than that of the flat silicon film. The proposed strategy and underlying theory can open up new avenues to realize ultrasharp resonances, which may promote the development of the potential meta-devices for nonlinearity, lasing action, and sensing.