Microcomb generation with simultaneous $chi^{(2)}$ and $chi^{(3)}$ nonlinearities brings new possibilities for ultra-broadband and potentially self-referenced integrated comb sources. However, the evolution of the intracavity field involving multiple nonlinear processes shows complex dynamics that is still poorly understood. Here we report on strong soliton regulation induced by fundamental-second-harmonic (FD-SH) mode coupling. The formation of solitons from chaos is extensively investigated based on coupled Lugiato-Lefever equations. The soliton generation shows more deterministic behaviors in the presence of FD-SH mode interaction, in sharp contrast to the usual cases where the soliton number and relative locations are stochastic. Deterministic single soliton transition, soliton binding and prohibition are observed, depending on the phase matching condition and coupling coefficient between the fundamental and second-harmonic waves. Our finding provides important new insights into the soliton dynamics in microcavities with simultaneous $chi^{(2)}$ and $chi^{(3)}$ nonlinearities, and can be immediate guidance for broadband soliton comb generation with such platforms.
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