Opto-acoustic resonance-enabled ultra-low phase noise microwave generation via coupled optoelectronic oscillators

Ultra-low phase noise microwave sources constitute critical components for advanced information and communication systems. This study presents a coupled optoelectronic oscillator (COEO) based on forward stimulated Brillouin scattering (FSBS) opto-acoustic resonance, achieving sub-Hertz linewidth and ultra-low phase noise microwave generation through coordinated opto-electro-acoustic multiphysics control. The design implements an FSBS fiber resonator that leverages group velocity matching between optical fields and transverse acoustic modes, generating narrowband gain via distributed opto-acoustic coupling, thereby significantly reducing reliance on high-Q filters. Optoelectronic feedback injection of FSBS signals into the fiber cavity enables locking of opto-acoustic oscillation mode, effectively suppressing side-mode competition and thermally induced phase noise. Experimental results demonstrate the output microwave signal linewidth of this COEO is 0.1 Hz, the phase noise at 10 kHz frequency deviation is lower than −130 dBc/Hz, maintaining merely 200 Hz frequency drift over 120-min operation. This work provides an ideal signal source combining ultra-low noise and high stability for next-generation wireless communications and precision radar systems while establishing pathways for nonlinear opto-acoustic coupling in complex media.