Theoretical And Experimental Study Of Ytterbium Doped Pm Fiber Laser

Over the past decades,passively mode-locked fiber lasers have been extensively applied in many fields such as material processing,frequency metrology,pure microwave generation,and THz generation.The nonlinear polarization evolution mode-locking technique is a prominent additive pulse mode-locking scheme.Compared with intrinsic saturable absorber(Semiconductor saturable absorber mirror or Graphene),it has many advantages such as high damage threshold,a fast response,low intrinsic noise,and insensitive to wavelengths;Compared with nonlinear loop mirror,it is easier to adjust and achieve self-starting.However,the primary drawback of this technique is sensitive to environmental fluctuation.Once the polarization state of the pulse changes,the mode locking state may be destroyed.One effective solution to eliminate the environmental instabilities and extend the laser applications to beyond laboratory environments is to replace the single mode fiber by polarization maintaining fiber.Schemes to achieve the NPE mode-locked laser in the PM fiber have been refined for years.But these schemes still need relative long fiber and there is no report on a repetition rate above 50 MHz in such schemes.Therefore,how to shorten the fiber length and improve the repetition rate of the pulse has become the key point of this kind of mode-locking technology.This thesis includes the following aspects:1.The laser transmission dynamics of ytterbium doped fiber is reviewed.The four order Runge Kutta in interaction picture is introduced,and the ytterbium doped ultrashort pulse oscillator in different dispersion regions is numerical simulated.The propagation of continuous light in ytterbium doped fiber is studied,based on the rate equation and stimulated Brillouin scattering;the propagation of ultrashort pulses in gain optical fiber is studied,based on the coupled Ginsberg Landau equation and rate equation.2.The vector evolution of the pulse in an all normal dispersion ytterbium doped fiber oscillator is studied.Firstly,the analytical solutions of cat ear spectrum under scalar conditions are introduced.Then,the vector model of pulse evolution is simulated based on the coupled Ginsberg Landau equation and the Jones matrix of the wave plate and polarization beam splitter.The state of the pulse in each polarization direction before entering the analyzer is studied.Experiments show that the time domain waveforms and spectral changes are similar to those of simulation results.It is concluded that the vector characteristics are derived from the different pulse shape from the two orthogonal polarization direction.3.Based on the preliminary theory and experimental preparation,the nonlinear polarization rotation mode-locking technique in the polarization maintaining fiber is explored.The optimal angle of bias welding is obtained by theoretical calculation,and the dynamic process of pulse evolution is studied by numerical simulation.The influence of the fiber length of the nonlinear polarization evolution section on the mode locking is also explored.Experimentally,using the optimal splicing angle predicted by the theoretical calculation,we have achieved an environmentally stable mode-locking fiber laser at 111-MHz repetition rate.Additionally,the noise performance of this PM fiber laser is accessed.The measured RMS timing jitter and amplitude noise are 6.41 fs and 0.0052% respectively [1 kHz,10 MHz],which are competitive to the low phase noise performance of the typical fiber laser.At last,the optimum splicing angle of analyzer for all polarization maintaining fiber based on the nonlinear evolution mode is explored.By calculating the transmittance curve,it is concluded that the optimum splicing angle of analyzer is always 45 degrees for the angle of arbitrary input deviation angle.