Nonlinear Dynamics Of Ultrafast Breather Laser And Their Intelligent Control

Ultrafast fiber lasers are widely used in micro-nano processing,precision measurement,ultrafast imaging,optical fiber communication and other fields.The traditional ultrafast laser emits soliton pulses,which have the limitations of difficult RF comb tuning and large comb spacing,making it difficult to meet the needs of diverse applications.Breathing soliton lasers can solve the bottleneck problems related to the difficulty of tuning RF combs of traditional ultrafast lasers.And it not only has important application prospects in the fields of precision spectral measurement,ultrastrong femtosecond pulses and adjustable optical combs,but also a universal nonlinear system for studying basic physical laws such as fractal dynamics,synchronization phenomena,and non-Hermitian optics.This paper mainly studies the breathing soliton ultrashort pulse and its nonlinear dynamics in ultrafast fiber lasers.The main research contents include multi-dimensional high-precision control of breathing solitons based on intelligent control system,fractal dynamics of breathing solitons,mechanism and control of subharmonic and non-subharmonic in breathing soliton molecules,and active regulation of extreme events in ultrafast lasers.The specific content is as follows:1.Based on the evolutionary algorithm,the intelligent generation of breathing solitons in passively mode-locked fiber lasers is realized.By constructing a compound objective function,the multi-dimensional and high-precision control of respiratory soliton parameters,including breathing period and breathing ratio,is realized for the first time.In addition,intelligent manipulation of the internal structure of respiratory soliton molecular complexes is demonstrated.This work lays the foundation for exploring and optimizing the complex dynamics of nonlinear systems.2.Revealed the fractal dynamics in the breathing soliton laser,using the fractal principle to increase the stability of the breathing soliton by 3500 times.For the first time,it was discovered that the ratio of the breathing frequency to the laser repetition rate(also known as the surround number)will appear a series of plateaus with the change of the pump current,and the values corresponding to these platforms show a classic fractal structure called Farey tree,and it is found that the dimension(0.87)of this fractal structure is the same as that of the devil’s staircase.We have further proved that a dense frequency comb that is not limited by the laser cavity length can be generated through fractal breathing solitons.The experiment shows that the comb density of fractal breathing solitons is 41 times higher than that of soliton lasers with the same cavity length.Therefore,fractal breathing soliton lasers provide a solution for sub-megahertz optical frequency combs.Theoretical simulations based on the nonlinear Schr(?)dinger equation also confirmed the experimental results.Due to the universality of the nonlinear Schr(?)dinger equation,this fractal phenomenon also widely exists in other physical systems,which will promote the research of fractals in related physical systems,such as fluid mechanics and condensed matter physics.3.Two kinds of subharmonic and non-subharmonic mode-locked breathing soliton molecules are found in ultrafast fiber lasers.The difference in dynamics of the two locked modes was compared.It is revealed that the instability of non-subharmonic breathing soliton molecules originates from radio frequency parametric processes,including higher harmonics,difference frequency,and four-wave mixing.The experimental phenomena were simulated using a discrete model of the generalized nonlinear Schr(?)dinger equation.The simulation results showed that the second-order dispersion,self-phase modulation,and dissipation effects played an important role in the generation of subharmonic and non-subharmonic waves of breather soliton molecules.4.The active control of extreme events(rogue waves)in fiber lasers is realized for the first time based on evolutionary algorithms.The algorithm was used to experimentally generate the strongest optical fury to date,with a spectral peak intensity32.8 times higher than the standard intensity threshold.Based on the precise control of the intelligent system,combined with ultrafast measurement technology and theoretical simulation,it is revealed that the symmetry breaking of the spectrum is the new generation mechanism of optical rogue waves.This work not only reveals a new generation mechanism of rogue waves,but also lays the foundation for the intelligent control of non-equilibrium physics.