Random Brillouin fiber laser for tunable ultra-narrow linewidth microwave generation.

Studies about random lasing phenomena taking place in disordered structures with amplification are gaining great interest, as they can support dual wavelength lasing without cavity length restriction and, hence, the tunable beat frequency in a microwave can be created in a random cavity and be amplified for applications in the information and communication technology. Here, we present a novel random Brillouin fiber laser scheme using the stimulated Brillouin scattering as gain and strong Rayleigh scattering feedback (10 km) in the single-mode fiber. The high degree of mutual coherence between the two Stokes beams from two different lasers leads to the generation of tunable ultra-narrow linewidth microwave signals (<10  Hz at 3 dB bandwidth) with a 70 dB contrast. This offers a simple and cost-effective design for microwave sources.