  The ultimate limits of performance for any classical optical system are set
by sub-wavelength fluctuations within the host material, that may be frozen-in
or even dynamically induced. The most common manifestation of such
sub-wavelength disorder is Rayleigh light scattering, which is observed in
nearly all wave-guiding technologies today and can lead to both irreversible
radiative losses as well as undesirable intermodal coupling. While it has been
shown that backscattering from disorder can be suppressed by breaking
time-reversal symmetry in magneto-optic and topological insulator materials,
common optical dielectrics possess neither of these properties. Here we
demonstrate an optomechanical approach for dynamically suppressing Rayleigh
backscattering within dielectric resonators. We achieve this by locally
breaking time-reversal symmetry in a silica resonator through a Brillouin
scattering interaction that is available in all materials. Near-complete
suppression of Rayleigh backscattering is experimentally confirmed through
three independent measurements -- the reduction of the back-reflections caused
by scatterers, the elimination of a commonly seen normal-mode splitting effect,
and by measurement of the reduction in intrinsic optical loss. More broadly,
our results provide new evidence that it is possible to dynamically suppress
Rayleigh backscattering within any optical dielectric medium, for achieving
robust light propagation in nanophotonic devices in spite of the presence of
scatterers or defects.
