Optophononic elliptical micropillars as ultrahigh frequency acoustic phonon transducers

The study of nanoscale acoustic phonons impacts quantum technologies, data communication, and sensing. GaAs/AlAs Fabry-Perot optophononic micropillar resonators confine near-infrared photons and sub-terahertz phonons, aiding the study of coherent acoustic phonons. The micropillar’s ellipticity splits optical resonance into two orthogonally polarized modes. We present a scheme to manipulate Brillouin scattering polarization rules using elliptical micropillars, accessing frequencies down to tens of GHz and allowing polarization filtering. Polarization states are controlled by the incident laser’s energy and polarization and the micropillar’s ellipticity. Optimal filtering conditions improve polarization-based Brillouin spectroscopy. In pump-probe experiments, phonon generation peaks when the laser wavelength matches the optical cavity resonance, and detection sensitivity is highest at the optical resonance slope. Elliptical optophononic micropillar resonators enhance both generation and detection processes using cross-polarized pump and probe beams, advancing micropillar acoustic resonators as efficient phonon transducers.