Second harmonic generation from bound-state in the continuum-hosted few-layers van der Waals metasurface

Area of Science:

• Optics and Photonics
• Materials Science
• Condensed Matter Physics

Background:

• Monolayer transition metal dichalcogenides (TMDs) coupled to bound-states in the continuum (BICs) show promise for high second harmonic generation (SHG).
• Weak exciton-photon coupling in surface-placed monolayer TMDs limits SHG efficiency.
• Achieving SHG in few-layer TMDs using BIC-inspired structures presents a significant challenge.

Purpose of the Study:

• To report a novel BIC-based metasurface using few-layer TMDs.
• To investigate the tunability and environmental robustness of these BICs.
• To achieve and quantify high second harmonic generation (SHG) efficiency in few-layer TMD metasurfaces.

Main Methods:

• Fabrication of few-layer TMD metasurfaces supporting BICs.
• Characterization of BIC quality factor (Q-factor) and tunability with varying meta-atom thickness.
• Calculation of SHG efficiency around BIC wavelengths.

Main Results:

• The metasurface sustains BICs with a high Q-factor, tunable by meta-atom thickness, and stable across environments.
• High second harmonic generation (SHG) conversion efficiency of 1.47 × 10^-4 was achieved with 6 µW incident power.
• The developed metasurface is ultra-thin, suitable for diverse linear and non-linear optical applications.

Conclusions:

• Few-layer TMD metasurfaces with BICs offer a promising platform for efficient nonlinear optics.
• This work provides a new route for developing next-generation post-silicon metasurfaces.
• The demonstrated tunability and robustness are crucial for practical device implementation.