  We demonstrate Kerr soliton frequency comb generation that is seeded by a
cascaded Brillouin scattering process. In this process, a pump laser is used to
generate multiple orders of Brillouin sidebands in a microresonator, which in
turn generate the soliton. In such a process, even orders of Brillouin
scattering sidebands are co-propagating with respect to the pump laser while
odd orders of Brillouin scattering are backwards propagating. In this work we
present the generation of forward propagating Kerr solitons via a forward
propagating second order Brillouin scattering process in a fused silica rod
resonator. Importantly, we show that the Brillouin scattering process can
bridge the gap between different microresonator mode families, such that the
repetition rate of the Kerr soliton is independent from the Brillouin gain
frequency shift (about 10 GHz in fused silica). In our work we demonstrate this
by generating soliton pulse trains with a repetition rate of 107 GHz. Our work
opens up a new way for using cascaded Brillouin lasing as a seed for
microresonator frequency comb generation. This can be of particular interest
for the realization of soliton frequency combs with low noise properties from
Brillouin lasing while still having arbitrary repetition rates that are
determined by the resonator size. Applications range from optical communication
to LIDAR systems and photonic signal generation.
