Parametric gain dynamics in normal-dispersion microresonators

Anomalous dispersion has long been regarded as a prerequisite for achieving parametric gain in Kerr nonlinear optics. Indeed, optical waveguides and microresonators with anomalous dispersion and Kerr nonlinearity have been widely utilized for optical parametric amplification (OPA), optical parametric oscillation (OPO), and frequency comb generation. Although modulation instability and mode-locked Kerr frequency combs have also been demonstrated in normal-dispersion microresonators, the detailed study of parametric gain dynamics is still lacking. Here, we systematically investigate the parametric gain dynamics in a high-Q normal-dispersion Si₃N₄ microresonator with a pump-probe method. Our experimental and theoretical analysis reveals a distinct gain-induced spectral evolution transitioning from Lorentzian dips to dual-peak structures. This study elucidates the mechanisms underlying optical parametric gain in normal-dispersion microresonators, offering enhanced theoretical insights.