Integrated unidirectional traveling-wave phonon waveguide parametric amplifier

Phonons, the quanta of elastic waves, play pivotal roles across a wide range of applications in both classical and quantum domains. Advancements in nanofabrication technologies have enabled phononic integrated circuits (PnICs) that provide nanoscale phonon control and enhanced interaction strengths, opening new avenues for fundamental research and innovative devices. Phonon amplifiers are essential active components of PnICs for advanced signal processing. However, traveling-wave integrated waveguide-based phonon parametric amplifiers have remained unrealized. Here, we demonstrate unidirectional traveling-wave phonon parametric amplification via the Stokes and Anti-Stokes processes of Brillouin scattering in a gallium nitride photonic-phononic hybrid integrated platform. This system offers strong confinement and low propagation losses for both optical and acoustic fields, facilitating robust photon-phonon interactions over extended spatial and temporal scales. With 50-mW on-chip pump power, we achieve 5.8 dB phonon gain (net gain -1.8 dB including propagation loss) while observing over 10 dB non-reciprocity between the forward and backward directions, realizing the first integrated unidirectional traveling-wave phonon parametric amplifier. Our work marks a significant advancement in integrated phononics and offers new opportunities for phononic-related information processing.