Research On Transient Spectral Characteristics Of Solitons In Ultrafast Fiber Lasers

Output pulse of ultrafast fiber laser has the advantages of narrow pulse width,wide spectrum and high peak power.It has been widely used in many fields such as optical communication,laser radar,ultrafast pump detection and laser micromachining.At the same time,many nonlinear transient phenomena of optical pulses have been observed in ultrafast fiber lasers,which has become an ideal platform for studying complex nonlinear dynamics of pulses.The dispersion Fourier transform（DFT）technology can map the spectrum of the incident optical pulse to the time-domain waveform,and it can be used to detect the spectrum of the output pulse of the ultra-fast fiber laser in real time.Researching the transient spectral characteristics of solitons in ultrafast fiber lasers is of great significance for revealing the physical mechanism of soliton evolution in laser cavity and optimizing the performance of fiber lasers.The main research contents of this thesis are as follows:1.The transient spectral characteristics of vector solitons in ultrafast fiber lasers are researched by DFT technology.A negative dispersion fiber laser based on carbon nanotubes is built.Polarization locked vector solitons,polarization rotation locked vector solitons and group velocity locked vector solitons are obtained respectively.The spectra of different types of vector solitons are observed in real time by DFT technology.The experimental results show that the polarization state of polarization locked vector soliton remains unchanged,and the transient spectra of its two polarization components do not change with time;The polarization state of polarization rotation locked vector soliton returns to the initial state after a cavity time period,and the transient spectra of its two polarization components change periodically with time;The central wavelengths of the transient spectra in both two polarization components of the group velocity locked vector soliton are different.The experiments reveal the "capture" characteristics of the two polarization components and form the group velocity locked vector soliton state.2.The negative dispersion cavity fiber laser based on carbon nanotubes is numerically researched,and the evolution of different types of vector solitons in the cavity is simulated.Keeping the intracavity gain unchanged,polarization locked vector solitons,polarization rotation locked vector solitons and group velocity locked vector solitons are obtained by changing the beat length in the cavity.The evolution process of the polarization characteristics of these soliton pulses with the number of transmission cycles in the cavity is analyzed,and its characteristics are consistent with the experimental results.3.The transient spectral characteristics of soliton pulsation in ultrafast fiber laser are researched by DFT technology.A net positive dispersion fiber laser based on carbon nanotubes is built,and the pulsating single soliton and pulsating double soliton are obtained respectively.Different pulsating solitons are observed in real time by DFT technology.The experimental results show that the width and energy of the transient spectrum of pulsating solitons change periodically,and the pulsating period of solitons is hundreds of times that of the cavity.By adjusting the pump power and polarization controller of the laser,the pulsating soliton molecule is also obtained.It is found that there are interference fringes in its transient spectrum,which is caused by the interference of two soliton spectra in the soliton molecule.