  The selection rules governing spontaneous Brillouin scattering in crystalline
solids are usually taken as intrinsic material properties, locking the relative
polarization of excitation and signal in bulk. In this work, we independently
manipulate these polarization states by means of optical resonances in
elliptical micropillars and demonstrate a polarization-based filtering scheme
for Brillouin spectroscopy in the 20-100 GHz range, important for telecom
applications. This strong modification of selection rules using elliptical
micropillars can be extended to any optical system with localized,
polarization-sensitive modes, such as plasmonic resonators, photonic crystals,
birefringent micro-, and nanostructures. Our polarization control protocol will
thus find applications in the engineering of light-matter interactions in
optomechanical, optoelectronic and quantum optics devices.
