We demonstrate a narrow-linewidth high-order-mode (HOM) Brillouin random fiber laser (BRFL) based on a long-period fiber grating (LPFG) and distributed Rayleigh random feedback in a half-open linear cavity. The single-mode operation of the laser radiation with sub-kilohertz linewidth is achieved thanks to distributed Brillouin amplification and Rayleigh scattering along kilometer-long single mode fibers whilst a few mode fiber-based LPFGs enable the transverse mode conversion among a broadband wavelength range. Meanwhile, a dynamic fiber grating (DFG) is embedded and incorporated to manipulate and purify the random modes, which hence suppresses the frequency drift resulting from random mode hopping. Consequently, the random laser emission with either high-order scalar or vector modes can be generated with a high laser efficiency of 25.5% and an ultra-narrow 3-dB linewidth of 230 Hz. Furthermore, the dependence of the laser efficiency and frequency stability on the gain fiber length are also experimentally investigated. It is believed that our approach could provide a promising platform for a wide range of applications such as coherent optical communication, high-resolution imaging, highly sensitive sensing, etc.

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-noiseinduced 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.

We theoretically investigate the forward stimulated Brillouin scattering (FSBS) of microfibers with elliptical transverse profile, revealing distinctive FSBS frequency dependence on the fiber geometry.

A high-order-mode Brillouin Random fiber laser with high purity and broadband tunability based on a long-period fiber grating and distributed Rayleigh scattering in optical fibers was demonstrated.

We proposed and demonstrated a high-efficiency Brillouin random fiber laser (BRFL) in a half-open linear random cavity incorporating with a self-inscribed dynamic fiber grating (DFG) for laser frequency stabilization. The DFG can be produced when the ion population distribution along erbium-doped fibers is periodically modulated by two coherent counter-propagating standing waves via the spatial hole-burning effect. Consequently, a BRFL with the linear half-open-cavity exhibited an optimized laser efficiency while the embedded DFG effectively purified the random modes and suppress the frequency drift caused by multiple random mode hopping. With a low laser threshold of 13.9 mW, the laser efficiency of up to 19.3% was observed, which is four times higher than that of the BRFL with a half-open ring cavity. It suggests that the proposed BRFLs could be beneficial to practical applications in fiber-optic sensing and coherent communication