Highly tunable birefringent phase-matched second-harmonic generation in an angle-cut lithium niobate-on-insulator...

Area of Science:

• Integrated photonics
• Nonlinear optics
• Materials science

Background:

• Phase-matched nonlinear wave mixing, such as second-harmonic generation (SHG), is essential for frequency conversion in integrated photonics.
• Achieving wide-tunable phase matching is critical for advanced photonic applications.
• Lithium niobate-on-insulator (LNOI) is a promising platform for integrated photonics due to its strong nonlinear properties.

Purpose of the Study:

• To propose and demonstrate a novel angle-cut ridge waveguide design for efficient and tunable second-harmonic generation (SHG) on the LNOI platform.
• To leverage the intrinsic birefringence of lithium niobate (LN) for flexible temperature tuning of phase matching.
• To overcome limitations of existing methods, such as spatial walk-off and the need for complex domain engineering.

Main Methods:

• Utilizing type-I birefringent phase matching (BPM) in angle-cut LN ridge waveguides.
• Employing temperature tuning to achieve phase matching at the telecommunication C band.
• Fabricating and experimentally characterizing the waveguide performance, including conversion efficiency and tuning slope.

Main Results:

• Demonstrated a normalized BPM conversion efficiency of 2.7%W^-1cm^-2.
• Achieved a temperature tuning slope of 1.06 nm/K.
• Effectively suppressed spatial walk-off and eliminated the requirement for periodic domain engineering.

Conclusions:

• The proposed angle-cut ridge waveguide design offers an effective approach for tunable nonlinear frequency conversion on the LNOI platform.
• This method overcomes key challenges in integrated nonlinear photonics and can be extended to other birefringent platforms.
• The work paves the way for broader applications of tunable nonlinear frequency conversion in integrated photonics.