Self-Injection Locking for Low Phase Noise Phonon\nLaser

Phonon\nlasers, as analogues of optical lasers, have received widespread\nattention in optomechanical systems. In this Article, we achieve phonon\nlaser self-injection locking using a microwave photonic architecture\nwith a feedback loop, which can be analyzed as an optoelectronic cavity.\nThe line width of the phonon laser with mechanical frequency of 4.97\nGHz is narrowed from 3 kHz to 150 Hz at room temperature. The phase\nnoise of the phonon laser can be as low as −95 dBc/Hz at a\nfrequency offset of 10 kHz, representing a decrease of 40 dB compared\nto the free-running state. Additionally, we lock two phonon lasers\nonto different cavity modes within the same fiber loop, achieving\na parallel output of the phonon lasers. This research yields promising\nresults in the development of a low-noise oscillator, a coherent phonon\nlaser, and mode-locked phonon lasers in optomechanical arrays.