Phonons in the GHz–THz range (wavelengths of 1–100 nm) offer a rich platform for exploring nanoscale wave phenomena and enabling new functionalities in nanoelectronics, photonics, sensing, and quantum technologies. Their strong interactions with other excitations in solids position them as key elements in the development of nanophononic devices and hybrid systems [1]. However, electrical generation of propagating acoustic waves remains limited to a few gigahertz due to transducer miniaturization constraints, while optical methods—though capable of reaching THz frequencies—have largely struggled to efficiently couple energy into traveling phonon modes.

This work is presented in two parts. First, we revisit phonon confinement using optophononic resonators based on AlAs/GaAs superlattices. These include planar Fabry-Pérot, topological, and adiabatic cavities, as well as 3D micropillars that co-confine near-infrared photons and hypersound at ~20 GHz within the same volume. This simultaneous confinement significantly enhances photon–phonon transduction in compact architectures.

Second, we demonstrate phonon guiding by etching these multilayers into waveguide geometries that support in-plane propagation of coherent acoustic waves. Using ultrafast transient-reflectivity pump-probe measurements, we generate and detect high-frequency phonons over remote regions, realizing a quasi-continuous acoustic source operating at room temperature. Interference measurements confirm mutual coherence between multiple spatially separated sources, demonstrating controllable, coherent transport.

Looking ahead, this platform is well-suited for programmable phononic control via spatial light modulation. By tailoring the number, location, and phase of optical excitation sites, it should be possible to synthesize arbitrary propagating acoustic waveforms. These results pave the way for reconfigurable nanophononic circuits and the integration of phononics with optomechanics, polaritonics, and quantum acoustics.

[1] Priya, Cardozo de Oliveira, E. R., and Lanzillotti-Kimura, N. D., Appl. Phys. Lett. 122, 140501 (2023)