Frequency conversion in nano-waveguides using bound-state-in-continuum.

Area of Science:

• Photonics
• Nonlinear optics
• Semiconductor nanophotonics

Background:

• Optical frequency conversion in nanophotonic devices demands high fabrication precision.
• Existing methods are limited by etch surface roughness and accuracy requirements.

Purpose of the Study:

• To introduce a novel waveguide design for optical frequency conversion utilizing bound-state-in-continuum (BIC) modes.
• To overcome fabrication limitations in nonlinear nanophotonic devices.

Main Methods:

• Adopting the bound-state-in-continuum (BIC) concept for waveguide frequency converter design.
• Utilizing gallium phosphide (GaP) as the nonlinear material.
• Implementing second-harmonic generation with horizontally polarized pump light at 1.55 µm phase-matched to vertically polarized BIC modes.

Main Results:

• A theoretical normalized frequency conversion efficiency of 1.1×10^4 % W^-1 cm^-2 was achieved using the fundamental BIC mode.
• The proposed BIC-based design requires patterning only a low-refractive-index strip on a nonlinear slab.
• The efficiency is comparable to conventional GaP waveguides, despite relaxed fabrication constraints.

Conclusions:

• Bound-state-in-continuum (BIC) modes offer a promising pathway for efficient optical frequency conversion in nanophotonic devices.
• This approach significantly reduces the stringent requirements on fabrication accuracy and etch surface roughness.
• The BIC-based design provides a viable alternative to conventional waveguides with comparable performance.