  The recent discovery of dissipative Kerr solitons in microresonators has
facilitated the development of fully coherent, chip-scale frequency combs. In
addition, dark soliton pulses have been observed in microresonators in the
normal dispersion regime. Here, we report bound states of mutually trapped
dark-bright soliton pairs in a microresonator. The soliton pairs are generated
seeding two modes with opposite dispersion but with similar group velocities.
One laser operating in the anomalous dispersion regime generates a bright
soliton microcomb, while the other laser in the normal dispersion regime
creates a dark soliton via Kerr-induced cross-phase modulation with the bright
soliton. Numerical simulations agree well with experimental results and reveal
a novel mechanism to generate dark soliton pulses. The trapping of dark and
bright solitons can lead to light states with the intriguing property of
constant output power while spectrally resembling a frequency comb. These
results can be of interest for telecommunication systems, frequency comb
applications, ultrafast optics and soliton states in atomic physics.
