Brillouin random lasing resonance enabled fast light and superluminal propagation in optical fibers.

We proposed and demonstrated fast light and superluminal propagation based on Rayleigh scattering-induced Brillouin random lasing resonance in optical fibers. A theoretical model of the proposed Brillouin superluminal propagation system has been established, detailing the principle of optical group velocity manipulation based on the combination of stimulated Brillouin scattering and Brillouin cross-gain modulation, for the first time to the best of our knowledge. Thanks to the randomly distributed Rayleigh scattering, Brillouin random lasing resonance with a single-longitudinal-mode lasing operation essentially contributes to fast light and superluminal propagation of the pump light signals propagating along a kilometer-long optical fiber. The temporal advancement, group velocity, and group index of sinusoidally modulated pump signals are thoroughly compared in experiments, which agree well with simulations. The dependence of the Brillouin gain fibers on the group velocity as well as the impact of Stokes power under different signal modulation frequencies on the broadening factor are systematically discussed and characterized. Furthermore, the Brillouin random lasing fast-light system is developed to offer a unique time-domain analysis solution for high-sensitivity fiber Bragg grating (FBG) temperature sensing scheme. Scalable sensitivity of the proposed sensing system can be achieved by applying different modulation frequencies. These findings may find wide potential applications in optical signal processing and hyper-sensitive detection.