  Mode-locked ultrashort pulse sources with a repetition rate of up to several
tens of gigahertz greatly facilitate versatile photonic applications such as
frequency synthesis, metrology, radar, and optical communications. Dissipative
Kerr soliton microcombs provide an attractive solution as a broadband,
high-repetition-rate compact laser system in this context. However, its
operation usually requires sophisticated pump laser control to initiate and
stabilize the soliton microcombs, particularly in millimeter-sized ultrahigh-Q
whispering-gallery resonators. Here, we realize a mechanically actuated soliton
microcomb oscillator with a microwave repetition rate of 15 GHz. This enables
direct soliton initiation, long-term stabilization, and fine tuning, where the
operation now lifts the prerequisite pump laser tunability that must be relaxed
if the technology is to be widely used outside the laboratory environment. We
reveal the prospects for using this method with a wide range of applications
that would benefit from mechanical soliton actuation such as optical clocks,
spectral extension, and dual-comb spectroscopy.
