  Forward stimulated Brillouin scattering (F-SBS) is a third-order
nonlinear-optical mechanism that couples between two co-propagating optical
fields and a guided acoustic mode in a common medium. F-SBS gives rise to
nonlinear wave mixing along optical fibers, which adds up with four-wave mixing
induced by the Kerr effect. In this work, we report the distributed mapping of
nonlinear wave mixing processes involving both mechanisms along standard
single-mode fiber, in analysis, simulation and experiment. Measurements are
based on a multi-tone, optical time-domain reflectometry setup, which is highly
frequency-selective. The results show that F-SBS leads to nonlinear wave mixing
processes that are more complex than those that are driven by the Kerr effect
alone. The dynamics are strongly dependent on the exact frequency detuning
between optical field components. When the detuning is chosen near an F-SBS
resonance, the process becomes asymmetric. Power is coupled from an
upper-frequency input pump wave to a lower-frequency one, and the amplification
of Stokes-wave sidebands is more pronounced than that of anti-Stokes-wave
sidebands. The results are applicable to a new class of distributed fiber-optic
sensors, based on F-SBS.

Optics