シリコンナイトライドマイクロ共振器における光誘起第二高調波発生の広帯域スペクトルマッピング

By employing a pump-probe technique for enhanced spectral mapping of the dynamics in nonlinear frequency conversion, we demonstrate that photo-induced second-harmonic generation (SHG) in silicon nitride (Si₃N₄) microresonators can persist when transitioning from the preferred doubly resonant condition-where the resonances of the optical harmonics are required to be matched-to a highly detuned state where the generated second harmonic is significantly shifted away from its corresponding resonance. This results in an unconventionally broad conversion bandwidth. Other intriguing phenomena, such as detuning-dependent all-optical poling and nonlinear multi-mode interaction, are also presented, to the best of our knowledge, for the first time with direct experimental evidence. Our findings provide new insights into the physics of photo-induced second-order (χ⁽²⁾) nonlinearity, highlighting its potential applications for nonlinear χ⁽²⁾ photonics in an integrated Si₃N₄ platform.