The Generation And Contorl Of Akhmediev Breathers In Fiber Laser

With the rapid development of optical communication,fiber lasers have great influence on scientific researches and technology applications due to their advantages of good beam quality,high coupling efficiency,wide coordination range,low laser threshold and high cost performance.Fiber lasers can produce not only continuous laser,but also ultrashort pulses with width in ps ~fs.The ultrashort pulses have the characteristics of high power and narrow pulse width.It can be used in laser ranging,optical fiber sensing,laser communication,biomedicine,national defense,military and other fields.Theoretically,the transmission of light pulses in the fiber system can be described by the nonlinear Schr?dinger equation.The NLSE includes many exact solutions,such as bright soliton solution,dark soliton solution,soliton solution on finite background and so on.The soliton solution on finite background can be divided into Akhmediev breather solution,Peregrine soliton solution,and Kuznetsov-Ma soliton solution.On the one hand,Akhmediev breathers can describe the modulation instability process.On the other hand,it can be used to generate ultrashort pulse sequences.In this paper,based on the simplified model of fiber laser,the propagation characteristics of Akhmediev breathers in fiber laser are studied numerically in this paper.The details are as follows:(1)The concept,classification and research process at home and abroad of solitons are introduced.The research status of optical fiber lasers at home and abroad and the research progress of solitons in fiber lasers are introduced.(2)The construction of theoretical model.Based on Maxwell's equations,the propagation equations of optical pulses in single-mode fibers,erbium-doped fibers and saturable absorbers are established.The step-by-step Fourier numerical simulation method is briefly introduced.(3)Based on the propagation model of optical pulses in fiber lasers,the transmission characteristics of Akhmediev breathers in fiber lasers are studied by using step Fourier method.The influences of average intracavity dispersion and small signal gain coefficient on Akhmediev breathers in fiber lasers are analyzed.The results show that the stability of Akhmediev breathers transmission is related to the average intracavity dispersion.The Akhmediev breathers with periodicity in time domain can propagate steadily in the breathing state when the interaction of intracavity dispersion and non-linear effect is balanced.At the same time,it is also affected by the small signal gain coefficient and saturation energy of the fiber laser.The larger the small signal gain coefficient,the higher the peak intensity of the pulse,the narrower the pulse width and the smaller the interval between adjacent pulses.In addition,the propagation of two different initial inputs,singlefrequency and periodic disturbances,in fiber lasers is also studied.Due to the modulation instability in optical fibers,both kinds of disturbances can excite a similar process comparing with the initial input waveform of the exact Akhmediev breathers.(4)Based on the propagation model of optical pulses in fiber lasers,the propagation characteristics of second-order Akhmediev breathers in fiber lasers are numerically studied.In theory,the second-order Akhmediev breathers can be considered as two first-order Akhmediev breathers colliding with each other.The results show that the second-order Akhmediev breathers can also excite the generation of ultrashort pulse sequence.And the peak power and period of the pulse are controlled by two first-order Akhmediev breathers.In addition,the propagation characteristics of two superimposed periodic and single frequency perturbations in fiber lasers are also studied.It is found that high peak pulses are generated during the transmission process.