Phase-Matched Second-Harmonic Generation in an On-Chip L iNbO3 Microresonator

The realization of an efficient nonlinear parametric process in microresonators is a challenging issue largely because of an inherent difficulty in simultaneously ensuring the phase-matching condition and a coherent multiple-resonance condition for all the waves participating in the nonlinear conversion process. Here, we demonstrate highly efficient second-harmonic generation in an on-chip LiNbO3 microresonator fabricated by femtosecond-laser direct writing. We overcome the above difficulty by selectively exciting high-order modes in the fabricated thin-disk microresonator. Thanks to the low optical absorption and high nonlinear optical coefficient of LiNbO3 crystal, we achieve a normalized conversion efficiency of 1.106×10-3/mW in the on-chip LiNbO3 microdisk with a diameter of approximately 102 μm.