Polarization-controlled Brillouin scattering in elliptical optophononic resonators.

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The fast-growing development of optomechanical applications has motivated advancements in Brillouin scattering research. In particular, the study of high-frequency acoustic phonons at the nanoscale is interesting due to the large range of interactions with other excitations in matter. However, standard Brillouin spectroscopy schemes rely on fixed wavelength filtering, which limits their usefulness for the study of tunable optophononic resonators. It has been recently demonstrated that elliptical optophononic micropillar resonators induce different energy-dependent polarization states for the Brillouin and the elastic Rayleigh scattering and that a polarization filtering setup could be implemented to increase the contrast between the inelastic and elastic scattering of the light. An optimal filtering configuration can be reached when the polarization states of the laser and the Brillouin signal are orthogonal to each other. In this work, we theoretically investigate the parameters of such polarization-based filtering techniques to enhance the efficiency of Brillouin scattering detection. For the filtering optimization, we explore the initial wavelength and polarization state of the incident laser, as well as the ellipticity of the micropillars, and reach an almost optimal configuration for nearly background-free Brillouin detection. Our findings are one step forward in the efficient detection of Brillouin scattering in nanostructures for potential applications in fields such as optomechanics and quantum communication.