Introducing a Symmetry-Breaking Coupler into a Dielectric Metasurface Enables Robust High-Q Quasibound States in the Continuum and Efficient Nonlinear Frequency Conversion

Abstract

Dielectric metasurfaces supporting quasi-bound states in the continuum (quasi-BICs) exhibit very high quality factor resonances and electric field confinement. However, accessing the high-Q end of the quasi-BIC regime usually requires marginally distorting the metasurface design from a BIC condition, pushing the needed nanoscale fabrication precision to the limit. This work introduces a novel concept for generating high-Q quasi-BICs, which strongly relaxes this requirement by incorporating a relatively large perturbative element close to high-symmetry points of an undistorted BIC metasurface, acting as a coupler to the radiation continuum. We validate this approach by adding a $\sim$100 nm diameter cylinder between two reflection-symmetry points separated by a 300 nm gap in an elliptical disk metasurface unit cell, using gallium phosphide as the dielectric. We find that high-Q resonances emerge when the cylindrical coupler is placed at any position between such symmetry points. We further explore this metasurface's second harmonic generation capability in the optical range. Displacing the coupler as much as a full diameter from a BIC condition produces record-breaking normalized conversion efficiencies >10${}^2$ W${}^{-1}$. The strategy of enclosing a disruptive element between multiple high-symmetry points in a BIC metasurface could be applied to construct robust high-Q quasi-BICs in many geometrical designs.

arXiv comment21 pages, 8 figures

References in corpus (13)

• Dielectric Metasurfaces for Complete Control of Phase and Polarization with Subwavelength Spatial Resolution and High Transmission
• Asymmetric metasurfaces with high-$Q$ resonances governed by bound states in the continuum
• Individual nanoantennas empowered by bound states in the continuum for nonlinear photonics
• Nonlinear metasurfaces governed by bound states in the continuum
• Giant nonlinear response at the nanoscale driven by bound states in the continuum
• Integrated gallium phosphide nonlinear photonics
• Enhanced High-Harmonic Generation from an All-Dielectric Metasurface
• Continuous wave second harmonic generation enabled by quasi-bound-states in the continuum on gallium phosphide metasurfaces
• High-harmonic generation from metasurfaces empowered by bound states in the continuum
• High-quality trapped modes in all-dielectric metamaterials
• Extreme Huygens' metasurfaces based on quasi-bound states in the continuum
• Imaging through Fano-resonant dielectric metasurface governed by quasi-BIC
• Near-unity third-harmonic circular dichroism driven by quasi-BIC in asymmetric silicon metasurfaces

Cited by in corpus (4)

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• Si Metasurface Supporting Multiple Quasi-BICs for Degenerate Four-Wave Mixing
• Dynamically Tunable Membrane Metasurfaces for Infrared Spectroscopy