Coherent acoustic phonon transport in optophononic waveguides

To achieve full control over acoustic phonons at ultrahigh frequencies, it is essential to characterize the phonon transport properties. Recent works have shown that surface acoustic waves at gigahertz frequencies can propagate over micrometer distances in different nanostructures such as nanowires, nanogratings, and nanoantennas. Here, we aim at investigating acoustic phonon transport by designing a GaAs/AlAs optophononic waveguide. Along the vertical direction of the waveguide, a Fabry-Perot cavity ensures an efficient confinement of acoustic phonons that has been demonstrated in planar and micropillar structures. In the lateral direction, the interface of air and semiconductor serves as an acoustic mirror to reflect phonons in the waveguide. We perform pump-probe experiments to generate coherent acoustic phonons at one position and detect them remotely on the waveguide. We analyze the signals originated by phonons generated in the pump position reaching the remote probe location, revealing a clear indication of phonon transport at room temperature. Our findings have potential applications in quantum technologies and data processing.