Slow & Fast Light And Superluminal Propagation Based On Stimulated Brillouin Scattering In Optical Fibers

Dynamic manipulation of the light speed has been of great importance owing to a number of practical applications in all-optical delay lines,high sensitive interferometer,light-mater interaction enhancement and microwave photonics,etc.In the past decade,slow and fast light based on stimulated Brillouin scattering(SBS)in optical fibers has shown the excellent flexibility to offer an efficient timing tool for all-optical delay,as well as the compatibility with the modern fibber-based communication system.In this dissertation,controlling light speed via SBS in optical fibers has been reviewed and deeply investigated.Some novel approaches for slow & fast light and superluminal propagation have been proposed and successfully demonstrated.Firstly,physical mechanism of SBS-induced light speed manipulation is analysised and reviewed in details.By using spontaneous Brillouin scattering,we proposed and experimentally demonstrated self-advanced fast light in a fiber ring.The advancement depends on the input optical power with a high slope efficiency of 1.67 ns/dBm which can be controlled by modifying the signal power or the fiber cavity loss.This scheme offers many advantages,including self-advancing without any external pump and high advancing efficiency.Superluminal propagation based on Brillouin lasing oscillation in optical fibers has been reported for the first time.We experimentally demonstrated negative-group-velocity propagation through a high-Q Brillouin fiber laser(BFL).The maximum advancement of 221.2 ns was observed with an ultra-high slope efficiency of 211.3 ns/dB.It indicates that this way is suitable for long-distance low-loss superluminal propagation in optical fibers.Moreover,highly nonlinear fiber can be employed to give further enhancement.The tunability of negative group velocity and group index turns out to be easily controlled by properly adjusting the input pump power and optical coupler ratio.The onset of multiple-longitudinal-mode(MLM)operation in long-cavity BFL directly leads to the fundamental limitation of superluminal-propagation distance.Here,a strategy to realize the extension of superluminal-propagation distance via a single-frequency BFL is proposed and experimentally demonstrated.The utilization of a saturable-absorber(SA)-based fiber loop guarantees the single-longitudinal-mode(SLM)operation in a long-cavity BFL.Consequently,the distance of superluminal propagation is well extended to over hundreds of meters in optical fibers.Furthermore,we reported optical bistability in the BFL with the SA of umpumed EDF.Large-region bistable region is found as 418.8mW in such a SA-based BFL with Brillouin gain media of 50 m single mode fiber.The tunability of the bistable region could be implemented by properly designing the Brillouin gain medium such as the fiber length and fiber type.Additionally,the relay of superluminal has been validated by cascading two platforms of BFLs.Finally,a compact tunable delay line via Brillouin lasing superluminal generation has been experimentally demonstrated.A 4-port optical circulator and a piece of polarization-maintained fibers(PMFs)are utilized to generate Brillouin lasing oscillation with the non-resonance pump scheme.Output signals exhibit a power-dependent tunable advancement over a wide-band working wavelength ranging from 1535 nm to 1565 nm.It indicates that such delay line is beneficial for potential applications in the fields such as data synchronism and fiber gyroscope.