Shallow-etched thin-film lithium niobate waveguides for highly-efficient second-harmonic generation.

Area of Science:

• Materials Science
• Photonics
• Nonlinear Optics

Background:

• High-fidelity periodic poling is crucial for efficient quasi-phase-matched second-harmonic generation (SHG) in thin-film lithium niobate (TFLN) waveguides.
• Utilizing quasi-TE polarized waveguide modes is essential for robust SHG performance.

Purpose of the Study:

• To demonstrate high-fidelity periodic poling over extended lengths in TFLN waveguides.
• To achieve efficient quasi-phase-matched second-harmonic generation at telecommunications wavelengths.
• To characterize the spectral linewidth and thermal tuning capabilities of the fabricated device.

Main Methods:

• Fabrication of a shallow-etched ridge waveguide in x-cut magnesium oxide doped TFLN.
• Accurate periodic poling over a 5 mm length.
• Non-destructive characterization using confocal scanning second-harmonic microscopy.

Main Results:

• Demonstrated high-fidelity poling over long lengths.
• Achieved a second-harmonic conversion efficiency of up to 939 %/W (length-normalized 3757 %/W·cm²).
• Observed a narrow spectral linewidth (1 nm) and precise thermal tunability (0.1 nm/°C) over 40 °C without efficiency loss.

Conclusions:

• The study successfully fabricated and characterized a TFLN waveguide with high-fidelity periodic poling.
• The device exhibits excellent performance for quasi-phase-matched second-harmonic generation, suitable for telecommunications.
• The demonstrated tunability and efficiency highlight the potential of this technology for advanced photonic applications.