Evaluating domain uniformity in PPLN via microscopy and terahertz waveform analysis

Area of Science:

• Materials Science
• Optics
• Solid State Physics

Background:

• Periodically poled lithium niobate (PPLN) is crucial for nonlinear optical (NLO) applications.
• Fabrication imperfections, like duty-cycle errors (DCEs), can significantly affect PPLN performance.
• Accurate characterization of domain structures is essential for optimizing device efficiency.

Purpose of the Study:

• To quantitatively analyze domain-width deviations in PPLN caused by DCEs.
• To compare the effectiveness of optical microscopy and terahertz (THz) waveform analysis in characterizing these deviations.
• To assess the impact of DCEs on the efficiency and spectral properties of NLO devices.

Main Methods:

• Quantitative analysis of domain-width deviations using optical microscopy.
• Complementary assessment of internal domain structures via THz waveform analysis.
• Theoretical modeling to predict efficiency reduction and spectral distortions.

Main Results:

• Microscopy revealed significant domain-width differences between top and bottom surfaces due to poling asymmetry.
• THz analysis showed microscopy can overestimate irregularities, especially for shorter quasi-phase-matching (QPM) periods.
• Domain-width deviations increased from 3.8% (400 µm QPM period) to 8.8% (75 µm QPM period).
• DCEs caused a ~5% efficiency reduction for first-order QPM, increasing exponentially to ~30% at the third order, introducing spectral pedestals.

Conclusions:

• Combining optical microscopy and THz analysis provides reliable quantitative benchmarks for PPLN domain engineering.
• Understanding and mitigating DCEs is critical for optimizing nonlinear optical device performance.
• The study highlights fabrication challenges at shorter QPM periods and their impact on device efficiency.