Study Of Soliton Dynamics In Spatiotemporal Mode-locked Multimode Fiber Laser

With the influence of higher-dimensional effect,such as modal dispersion,self-imaging and random coupling,the nonlinear transmission process of ultrafast laser in multimode fiber shows extremely complex dynamic characteristics and complex physical mechanism,and can provide a new experimental platform for the studies of interdisciplinary nonlinear problems.Therefore,it is of great significance to observe the nonlinear dynamic of multimode ultrafast laser in real time,study the physical mechanism in it and carry out interdisciplinary analogy analysis.However,the realization of this goal poses new challenges to the real-time optical measurement technology,particularly real-time acquisition of multi-dimensional information,accurate synchronization of multi-channel information,high temporal-frequency resolution,long recording time and so on.To address these problems,in this thesis,starting from the theoretical model of spatiotemporal mode-locked(STML)multimode fiber laser,we build up a spatiotemporal mode-locked multimode fiber laser,develop the real time multi-speckle spectral-temporal measurement technology(MUST)and study the nonlinear dynamics of spatiotemporal modelocked multimode ultrafast laser with analyzing the physical mechanism combined with theoretical simulation.The main achievements includes:(1)Based on the generalized multimode nonlinear Schrodinger equation,the simulation model of the STML multimode fiber laser and its three-dimensional(3D)numerical simulation platform were established.The spatial filter function deviated from the center of the fiber core is introduced into the model to realize versatile laser dynamics,which breaks through the limitation that the traditional one-dimensional model cannot observe the 3D picture.The numerical simulation results show the 3D temporal-spatial-spectral characteristics of the STML fiber laser.Theoretically demonstrate the dynamics including pulsation,soliton molecular vibration and soliton explosion in the STML multimode fiber laser.(2)The STML multimode fiber laser and the speckle resolved real-time temporal spectral measurement system consists of signal spatial amplification,time division multiplexing speckle information acquisition,time stretching and real-time acquisition were studied,which realizes speckle resolve multi-dimensional real-time synchronous observation in time,space and spectrum for the first time,with the temporal resolution of 12.5 ps,the spectral resolution of0.02 nm,and the spatial resolution of 10 μm.The characteristics and the speckle diversity of the 3D solitons were studied in temporal-spatial-spectral dimensions.The dynamics of the STML in birth,splitting,breathing and annihilation were measured,the spatiotemporal interaction of 3D solitons was further studied by using data processing methods such as field autocorrelation.By expanding the number of spatial channels of the MUST measurement system,higher dimension evolutions of multipulse STML were measured and analyzed.The fast mode decomposition algorithm was developed to calculate the transverse distribution of spatiotemporal mode locking.The transverse distribution of the STML multimode fiber laser measurement system and the mode decomposition of the STML were studied.The energy proportion and mode decomposition reconstruction diagram of the first 300 modes were obtained.(3)The numerical simulation and experimental research platform of 3D soliton molecules were established,and the speckle different real time temporal spectral dynamics of 3D soliton molecular were studied.The diversely temporal spectral dynamics of 3D soliton molecules and the physical mechanism of transient phenomena were experimentally and theoretically studied,such as the interaction between soliton molecules and free running solitons,the interaction within soliton molecules,and long term spatiotemporal evolution of soliton molecules.Numerical simulation showed that the difference of pulse evolution among modes is the reason for the diversification of speckle dynamics.Through 3D optical analogy,a powerful interdisciplinary method was provided to solve the problems that could be difficult to be verified directly in experiments in molecular science.