  The stabilization of optical frequency comb conventionally relies on active
electronic feedback loops and stable frequency references. Here, we propose a
new approach for autonomous frequency locking (AFL) to generate a zero-offset
frequency comb based on cooperative nonlinear optical processes in a
microcavity. In a simplified few-mode system, AFL enables the concept of
fractional harmonic generation as a zero-offset multi-laser reference for
measuring the carrier envelope offset frequency ($f_{\mathrm{ceo}}$) of
frequency combs spanning less than one octave, such as 1/3 octave. Combining
with Kerr comb generation in a microcaivity, AFL is further applied to directly
generate zero-$f_{\mathrm{ceo}}$ soliton comb that is robust against
fluctuations in pump laser and cavity resonances. Numerical simulations
validate the AFL scheme, showing good agreement with analytical prediction of
the locking condition. This work presents a new pathway for exploring novel
frequency locking mechanisms and technologies using integrated photonic
devices, and also appeals further investigations of cooperative nonlinear
optics processes in microcavities.
