Laser Linewidth Compression in Cascading Brillouin Random Fiber Lasers

Cascaded Brillouin random fiber lasers (BRFLs) with laser linewidth compression were theoretically and experimentally demonstrated. Thanks to photon-phonon coupled interplay as well as randomly distributed feedback along silica fibers, the coherent time of cascading BRFL radiation is significantly prolonged whilst the phase noise is further suppressed, albeit with a quantum-noise-induced linewidth narrowing limit. To validate it, the linewidth narrowing ratio in BRFLs, defined as the ratio of the Brillouin pump and its sequent order of Stokes linewidth, was carried out and exhibited a dependence on the Brillouin pump linewidth, which is in good agreement with theoretical predictions. Furthermore, the relative intensity noises of cascading BRFLs were also investigated and discussed.