Enhancing second harmonic generation by merging symmetry-protected BIC and Fabry-Perot BIC.

Area of Science:

• Photonics and Nanotechnology
• Nonlinear Optics

Background:

• Second harmonic generation (SHG) is crucial for integrated optical devices.
• Nanosacle SHG faces challenges in conversion efficiency.

Purpose of the Study:

• To numerically demonstrate boosted SHG conversion efficiency by merging symmetry-protected bound state in the continuum (BIC) and Fabry-Perot BIC.
• To propose a metasurface design for merged BIC support.

Main Methods:

• Numerical simulation of a lithium niobate-based silicon grating metasurface.
• Investigating the merging of symmetry-protected BIC and Fabry-Perot BIC by adjusting grating height.
• Analyzing the quality factor (Q factor) and SHG conversion efficiency.

Main Results:

• Achieved merged BIC with a Q factor exceeding 10^7 over a wide asymmetry range (|α|<±0.2).
• Demonstrated a 0.11% SHG conversion efficiency at 1 kW/cm^2 input intensity for α=0.2.
• Observed a four-orders-of-magnitude enhancement in SHG efficiency compared to isolated BIC.

Conclusions:

• Merging BICs provides a viable method for boosting nanoscale SHG conversion efficiency.
• The proposed metasurface design enables high-efficiency, ultra-compact light sources.
• The merged BIC demonstrates robustness against fabrication imperfections.