  Temporally stabilized optical pules, confined in microresonators driven by a
continuous-wave laser, have attracted tremendous attention due to their
fascinating features with many applications. Here we report the observations of
mode-locked platicon frequency microcomb formation in normal dispersion
dispersion-managed microresonators operating at microwave K-band repetition
rate for the first time. Facilitated by the thermally controllable modulated
background induced by avoided mode-crossings, various platicon bound state
patterns with regular and irregular temporal separation are stably generated
due to an additional balance between repulsive and attractive forces resulting
from non-trivial interpulse and background electromagnetic field interactions.
The number of mode-locked pulses can be switched by forward- and
backward-cavity pump detuning and, with increasing pump power, result in
stationary bound-state complexes. These experimental observations are in
accordance with our nonlinear numerical simulations that includes avoided
mode-crossing, anomalous fourth-order dispersion and quality-factor spectral
filtering. The observed platicon mode-locked pulses have broad spectral
profiles overlapping Kelly-sideband-like parametric oscillation. The
single-sideband phase noise of microcomb repetition rate is characterized for
the different mode-locked states, comparable with electronic microwave
oscillators. The ability to achieve mode-locking in dispersion-managed
microresonators provides a platform to reduce pulse timing jitter and enrich
the exploration of ultrafast phenomena in microresonators.
