Efficient second-harmonic generation based on off-Γ merging bound states in the continuum.

Area of Science:

• Photonics and Materials Science
• Nanotechnology and Metasurfaces

Background:

• Ultracompact devices for second-harmonic generation (SHG) are crucial for various applications.
• Existing nanostructures often suffer from radiative and scattering losses, limiting performance.

Purpose of the Study:

• To propose and demonstrate a novel approach for enhancing SHG efficiency in ultracompact devices.
• To leverage bound states in the continuum (BICs) for improved performance in nonlinear optical applications.

Main Methods:

• Engineered a merging bound state in the continuum (BIC) at an off-Γ point in reciprocal space.
• Utilized anisotropic lithium niobate materials for device fabrication.
• Investigated the impact of BIC on radiative loss, scattering loss, and quality factor.

Main Results:

• Achieved a significant reduction in radiative and scattering losses.
• Demonstrated a substantial enhancement in the quality factor of the nanostructure.
• Obtained a noteworthy SHG efficiency of 3.7% at an incident angle of 10° with a pump intensity of 2 kW/cm².

Conclusions:

• The merging BIC in lithium niobate offers a promising route to high-performance, ultracompact SHG devices.
• This research validates the use of nanoengineering principles on traditional nonlinear crystals for advanced metadevices.
• The developed approach outperforms alternative nanostructures for SHG applications.