  Recent advances in design and fabrication of photonic-phononic waveguides
have enabled stimulated Brillouin scattering (SBS) in silicon-based platforms,
such as under-etched silicon waveguides and hybrid waveguides. Due to the
sophisticated design and more importantly high sensitivity of the Brillouin
resonances to geometrical variations in micro- and nano-scale structures, it is
necessary to have access to the localized opto-acoustic response along those
waveguides to monitor their uniformity and maximize their interaction strength.
In this work, we design and fabricate photonic-phononic waveguides with a
deliberate width variation on a hybrid silicon-chalcogenide photonic chip and
confirm the effect of the geometrical variation on the localized Brillouin
response using a distributed Brillouin measurement.
