The Generation And Transmission Of First-order Dark Rogue Wave In Fiber Laser

Optical rogue wave is a current research hotspot in the field of nonlinear optics.Although the rogue wave is difficult to predict,it has the characteristics of narrow pulse width and high amplitude,so can apply to generate ultrashort pulses.Ultrashort pulses can be used in laser ranging,laser radar,precision measurement,optical fiber sensing,optical communication,biomedicine and so on.Optical rogue waves can be divided into bright rogue wave and dark rogue wave.In recent years,the dark rogue wave has gradually attracted people's attention.Theoretically,it was found that the optical dark rogue waves were generated in the vector system which include the coupled nonlinear Schrodinger equation ? the three-wave resonant interaction equation and the long-wave short-wave resonance equation.This paper is mainly based on the simplified fiber laser model,using the coupled nonlinear Schr?dinger equation in the vector system to numerically study the transmission characteristics of optical dark rogue wave in fiber laser.The results can provide certain theoretical basis for the research of dark rogue waves in experiment.The content of this article is as follows:(1)The concept and the research fields of rogue waves are introduced,then focus on the origin and development of optical rogue waves.Moreover,explain the research status of optical dark rogue waves,and finally discuss the research of the rogue waves in fiber lasers.(2)A simplified fiber laser model is proposed,which is processed in sections.The modified coupling nonlinear Schrodinger equation is used to derive the transmission equations of the first-order optical dark rogue wave in each part of the fiber laser.Then the split-step Fourier transform numerical method is briefly introduced.(3)Mainly based on the coupled nonlinear Schrodinger equation as a theoretical model,the generation of the first-order dark rogue wave in fiber laser is numerically studied.Firstly,the influence of related factors such as the intra-cavity average dispersion and small signal gain coefficient for the dark rogue wave in fiber laser are analyzed.The results show that the transmission of dark rogue wave in fiber laser is related to the intra-cavity average dispersion.When the interaction of the intra-cavity average dispersion and the nonlinear effect is balanced,the exited dark rogue wave will split more secondary dark rogue waves which also have space-time local characteristics.At the same time,as the small signal gain coefficient gradually increases,the dark rogue wave will more quickly split into secondary dark rogue wave during transmission,and the local characteristics of the secondary dark rogue wave will be enhanced.In addition,the output state of the first-order optical dark rogue wave can be controlled by the polarization controller.Finally,through the method of optical chopping,two long-distance dark pulses are obtained from the first-order dark rogue waves.(4)The coupled nonlinear Schr?dinger equation was used as a theoretical model to study the interaction of two first-order dark rogue waves in a normal dispersion single-mode fiber.Based on the exact solution of first-order dark rogue wave,the interaction between two adjacent first-order dark rogue waves is discussed in terms of spacing,phase and ratio of amplitude coefficients using split-step Fourier numerical simulation.Moreover,based on the exact solution of the second-order dark rogue wave,the nonlinear interaction of two first-order dark rogue waves is discussed.The results show that the interaction of two adjacent in-phase first-order dark rogue waves will generate "twisted" dark rogue waves.Compared to the energy diffusion of a single dark rogue wave,the "twisted" dark rogue wave can split and form multiple secondary dark rogue waves.However,the initially excited spatial position of the "twisted" dark rogue wave deviates from the original position of the first-order dark rogue wave,which is related to the amplitude coefficient ratio of two adjacent dark rogue waves.Then the second-order dark rogue wave can be regarded as a nonlinear superposition of two first-order dark rogue waves,which is slightly similar to the interaction between two adjacent first-order dark rogue waves.