Tunable Bistability In Hybrid Brillouin-erbium Fiber Laser Based On Saturable Absorber

Optical bistability phenomenon is a hysteresis feedback effect that occurs in the optical system.Because of this phenomenon,the optical output will have two different stats,and the real system state is determined by the changing process of the input signals.And this phenomenon can be applied in lots of fields,such as optical logic gates,optical switches,optical storage technology.Because of the potential applications of optical bistability,the research and exploration of bistability do attract a large number of researchers in the field of optical.Particularly,the fiber laser based on stimulated Brillouin scattering has strong point in many aspects,and it has great stability at room temperature,perfect compatibility with modern communication systems,and many other important properties of the advantages of portability.The bistability in fiber device has been widely studied in all aspects during the past decades.This thesis is mainly depth study and discussion of optical bistability in the Brillouin and erbium-doped hybrid fiber laser with saturable absorber and ring-cavity.And in the area of continuously tunable bistability,our experiment in this thesis has made some achievements.Firstly,the thesis mainly discusses the basic theory of the laser,and the development and application of fiber lasers.The realization method as well as the measurement of single longitudinal mode laser has also been explored,and short cavity method,the complex cavity method,the stimulated Brillouin scattering method and the saturable absorber method are mostly used to realize the single longitudinal mode,and these methods are theoretically discussed in mechanism.After realization of the single longitudinal mode,measurement is followed.There are methods listed in detail that can prove the single longitudinal mode output and measure the linewidth of the output,such as the scanning F-P interferometer,the selfbeat method,the delay heterodyne method,non-delay heterodyne method were discussed.Secondly,this paper studies the optical bistability phenomenon,as well as its practical application and the principle of its implementation.Then the influencing parameters of the bistability were analyzed.According to the influence of the loss coefficient(as well as gain coefficient)of laser cavity on the bistable region,the loss coefficient affects the bistable region.And this relation between cavity loss and bistable region can be used to realize the continuously tunable bistability.This thesis put forward a hybrid pumps with ring cavity to continuously change the cavity loss,in which a tunable laser source injected into the laser cavity works as the source to stimulate Brillouin scattering and another 980-nm pump plays the roll of an internal Erbium-doped fiber amplifier with the Erbium-Doped fiber in cavity.By the combined of two pump,the cavity gain / loss factor can be controlled,as a consequence of this,the pump power will affect the bistable region of the laser.Ultimately,by hybrid pump,we realize continuously tunable bistable region.Finally,we introduce Sagnac loop with saturable absorber,which plays the roll of self-tracking filter.The filter has effect on the output,and select the specific mode to achieve single longitudinal mode with ultra narrow linewidth.According to the thesis,we can get draw the bistable area of a dualpump laser,and realize the accurate control of the bistable region.The experimental results provide an important basis for the practical application of optical bistability.