Power Clamping in Second Harmonic Generation Within an On-Chip Lithium Niobate Microdisk

On-chip lithium niobate (LN) microresonator is regarded as a promising candidate for power clamping in second harmonic generation (SHG) owing to its high-quality factor, small mode volume, and large nonlinear coefficient. To date, various theories have been proposed to describe the three-wave mixing mechanism within a LN microresonator, while a comprehensive understanding of mode evolution and its impact on nonlinear frequency conversion efficiency especially for power clamping, is still limited. Here, the dual-resonance detuning dynamics are investigated theoretically and the effect of mode chord angles on nonlinear frequency conversion efficiency is analyzed. Experimentally, two distinct power clamping points, including the normalized conversion efficiency of ≈38% mW⁻¹ and output power of ≈1.2 mW, are separately observed in the same microresonator, consistent with the theoretical model. The results clarify the physical mechanism behind the power clamping in the observed SHG and offer a unique approach to achieving efficient and powerful SHG in LN microresonators.