  Dissipative Kerr solitons are localized structures that exist in optical
microresonators. They lead to the formation of microcombs --- chip-scale
frequency combs that could facilitate precision frequency synthesis and
metrology by capitalizing on advances in silicon photonics. Previous
demonstrations have mainly focused on anomalous dispersion microresonators.
Notwithstanding, localized structures also exist in the normal dispersion
regime in the form of circulating dark pulses, but their physical dynamics is
far from being understood. Here, we report the discovery of reversible
switching between coherent dark-pulse Kerr combs, whereby distinct states can
be accessed deterministically. Furthermore, we reveal that the formation of
dark-pulse Kerr combs is associated with the appearance of a new resonance, a
feature that has never been observed for dark-pulses and is ascribed to soliton
behavior. These results contribute to understanding the nonlinear physics in
few-mode microresonators and provide insight into the generation of microcombs
with high conversion efficiency.
