  Different from the Kerr effect,stimulated Raman scattering (SRS) is a delayed
response to molecular vibrations in materials. In microcavities, when driven in
an anomalous group velocity dispersion (GVD) regime, SRS typically leads to
self-frequency shift of solitons and generation of breather solitons which have
been verified both theoretically and experimentally. However, when driven in a
normal GVD regime, recent theoretical work predicts that SRS can cause the
locking of switching waves (SWs) and thus support bright moving localized
structures (LSs), which we term as Kerr-Raman solitons (KRSs). Limited by the
design of suitable experimental parameters, experimental observation of the
KRSs is not achieved yet. Here, we provide numerical investigation, and to our
knowledge, the first experimental observation of these SRS enabled KRSs in a
fiber Fabry-Perot (FP) resonator with ultra-low normal GVD. Such Kerr-Raman
solitons exhibit localized temporal features with strong oscillations at ~13
THz local frequency on the top of a flat-top pulse. The corresponding spectrum
is a low-noise and broadband Kerr comb with typical platicon-like spectrum in
the center and two Raman Stokes and anti-Stokes peaks located near 13 THz away
from the center. With such SRS enabled broadband Kerr comb, we have achieved a
KRS spectrum with a repetition rate of ~3.68 GHz and a -40 dB spectral width of
260 nm. The corresponding comb tooth count is >9000, covering the S+C+L
telecommunication bands. Moreover, the formation process of such KRSs is also
revealed, and it is found that the GVD plays a key role in its generation. Our
work will help to advance the study of the dynamics of optical frequency combs
under the influence of SRS, as well as providing a broadband coherent
mode-locked optical source for wide applications.
