Ultra-Low-Noise and High-Stability Microwave Generation Based on Self-Oscillating Brillouin Cavity

Ultra-low noise microwave signals with exceptional stability are crucial for modern scientific applications. Here, we propose and experimentally demonstrate a novel microwave generation scheme based on self-oscillating Brillouin cavity. The system achieves linewidth narrowing by cascaded stimulated Brillouin scattering (SBS) and frequency-shifted optical injection locking (FSOIL) using dual mutually stabilized Brillouin fiber lasers (BFLs) inside a fiber ring resonator without any active optoelectronic feedback. Based on the self-oscillating architecture, it successfully removes the dependence on external microwave sources and greatly simplifies the system structure while maintaining ultra-low phase noise (< -120dBc/Hz @ 10kHz offset). More importantly, the microwave signal can dynamically track the longitudinal mode change of the cavity, and the synchronized feedback ensures excellent long-term stability of the microwave output while optimizing the FSOIL locking effect, maintaining kHz-level frequency stability over 1500s and <1% power deviation within 10 minutes. The proposed scheme achieves highly stable and ultra-low noise microwave generation in a robust and efficient manner, showing good potential for next-generation photonics microwave systems.