  Stimulated Brillouin scattering (SBS) in low-power and compact
microresonators has created a new field in cavity nonlinear photonics due to
the marriage between acoustic and optical signal processing. Considering the
fundamental differences between backward SBS and forward SBS processes, it is
challenging to observe the coexistence of both processes in the same
microresonator, as well as the photon noise suppression for the forward
stimulated Brillouin laser (FSBL). In this paper, we demonstrate the first
20-dB-noise-squeezed FSBL generation excited by the coexisting backward SBL
(BSBL) in an ultrahigh-quality-factor Fabry-Perot (FP) microresonator based on
multimode fiber (MMF). Multiple FSBLs and BSBLs are cascaded by multiple
intermodal SBS processes in the multimode microresonator, where the cascaded
process between backward SBS and forward SBS process (pump-BSBL-FSBL) provides
a route towards additional noise squeezing, rendering the FSBL phase noise to
be -120 dBc/Hz at 1 MHz offset frequency. Furthermore, we demonstrate the first
Brillouin-Kerr soliton from a high-order BSBL, which also coexists with FSBLs.
Our experimental results show the potential of MMF FP microresonator as an
ideal testbed for high-dimensional nonlinear cavity dynamics and laser source
with ultrahigh coherence.
