Abstract
Optical frequency combs are crucial for both fundamental science and applications that demand a wide frequency range and ultra-high resolution. Recent advances in optical frequency combs based on the nonlinear Kerr effect in microcavities have opened up new opportunities with such compact platforms. Although optical frequency combs have previously been well studied in the steady state, some fundamental perspectives such as nonlinear phase modulation during comb generations are yet explored. Here we demonstrate transient nonlinear dynamics during the formation of optical frequency combs inside a Kerr microcavity. We show that gain spiking forms due to nonlinear phase modulation causing comb lines' self-detuning from nearby cavity resonances, which provides one key mechanism to stabilize optical frequency combs. Moreover, we have observed nonlinear beating by injecting an external probe to examine nonlinear cross-phase modulation between comb lines. These nonlinear dynamics reveal the hidden features of self-stabilization and cross modulation during transient comb generations, which may enable new applications in mode-locking comb and tunable comb generation in microcavities.
Highlights
We show that gain spiking forms when nonlinear phase modulation plays a major role in self-detuning the nearby cavity resonances, effectively regulating gain and loss balance for each comb line
The most influential one is the pump-induced self-phase modulation (SPM) to itself and the cross-phase modulation (XPM) to signals and idlers [9,24]. These nonlinear phase modulations (NPM, including SPM and XPM) effectively alter the effective path lengths photons undergo inside the cavity, changing their resonances
Detuning terms of each beam around the central cavity resonances are carefully tuned to maintain the phase matching condition. This process is complicated by the extra nonlinear phase terms, e.g. SPM and XPM
Summary
We show that gain spiking forms when nonlinear phase modulation plays a major role in self-detuning the nearby cavity resonances, effectively regulating gain and loss balance for each comb line. The external injected strong pump through degenerate parametric FWMs converts energy to signal and idler beams 2ω ω ω , against cavity decay/loss above the threshold condition.
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Published Version
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