Acousto-optic coupling in phoxonic-plasmonic crystal nanobeam cavities

We investigate the enhancement of acousto-optic (AO) coupling using a Ag/GaAs heterogeneous phoxonic crystal nanobeam cavity. Because of the Ag layer, the cavity structure hybridizes surface plasmons and photons, squeezing the optical energy into a smaller region near the GaAs/Ag interface. The photonic cavity modes highly match the phononic cavity modes in space in the cavity. Because of the mode similarity, the AO coupling is stronger at near-infrared wavelengths. We show that the interface effect by the acoustic displacement field dominates the AO coupling enhancement. Small photonic mode volume and high spatial matching between the phononic and photonic cavity modes enhance the photonic resonance wavelength shift by one order of magnitude. The proposed structure enables applications of strong AO and photon-phonon interaction in subwavelength nanostructures.