Quasi-BICs enhanced second harmonic generation from WSe₂ monolayer.

Area of Science:

• Photonics
• Materials Science
• Nonlinear Optics

Background:

• Quasi-bound states in the continuum (quasi-BICs) are crucial for advanced optical devices and nonlinear optical processes.
• Engineering quasi-BICs in silicon metasurfaces offers a promising platform for optical applications.

Purpose of the Study:

• To experimentally achieve tunable, robust quasi-BICs resonances in a multiple-hole silicon metasurface.
• To demonstrate enhanced second-harmonic generation (SHG) in a 2D material by coupling it to quasi-BICs.

Main Methods:

• Fabrication of a multiple-hole silicon metasurface to engineer quasi-BICs.
• Angle-resolved spectroscopy to characterize the quasi-BICs mode and its dispersion.
• Coupling a monolayer of tungsten diselenide (WSe2) to the metasurface to study nonlinear optical enhancement.

Main Results:

• Achieved tunable and robust quasi-BICs resonances in the engineered silicon metasurface.
• Observed flat bands with minimal dispersion in the quasi-BICs mode across a wide range of incident angles.
• Demonstrated a significant enhancement of SHG from the WSe2 monolayer, exceeding two orders of magnitude, due to strong local electric fields and high state density of quasi-BICs.

Conclusions:

• The engineered silicon metasurface effectively hosts quasi-BICs with desirable properties for nonlinear optics.
• Coupling 2D materials like WSe2 to quasi-BICs provides a powerful method for giant nonlinear optical enhancement.
• This work advances silicon photonics for enhanced nonlinear optical processes in 2D materials, paving the way for novel optical devices.