  Soliton frequency comb generation in coupled nonlinear microcavities is
attractive because a coupled microcavity offers more flexibility and
possibilities compared to a single nonlinear microcavity. In this paper, we
investigate how an amplifying auxiliary cavity affects the bistability region
of the main cavity and soliton frequency comb generation. When the auxiliary
cavity has a small gain, it can partially compensate for the loss of the main
cavity allowing the generation of soliton combs with a relatively low Q-factor
in the main cavity. A low Q-factor microcavity would reduce the difficulty of
fabrication and extend the microcavity platform to different types of
materials. However, if the gain of the auxiliary cavity is too large, a
frequency comb cannot be generated because the coupled nonlinear microcavity
system is no longer dissipative. Our results provide a theoretical
understanding and experimental guidance for the bistability region and soliton
frequency comb generation in coupled nonlinear microcavities with an amplifying
auxiliary cavity. The results will facilitate the development of chip-scale
integrated optical frequency comb sources.
