Ultrashort Pulse Ytterbium Doped Fiber Lasers And Their Tunable Characteristics Research

Ultrashort pulse laser has very important applications in optical communication,laser detection,diagnosis,laser processing,fast laser ignition,laser radar,and many other fields.There are many different technologies to achieve ultrashort pulse laser.They are divided intoactively mode-locked technology,passively mode-locked technology,the combination of the first two kinds of ways,and synchronous pump technology etc.In this paper,the nonlinear polarization evolution passively mode-locked technology is adopted in ytterbium doped fiber laser for the ultrashort pulse laser.And we carried on the theoretical and experimental research about 1 ?m ultrashort pulse laser system.Besides,we also study the tunable characteristics of ytterbium doped mode-locked fiber laser with Sagnac loop spliced in high birefringence polarization-maintaining fiber and the polarization controller.The specific research work and the experiment results are as follows:First of all,we study the generation mechanism of ytterbium doped mode-locked fiber and explain the nonlinear polarization evolution mode-locked technology in theory.In order to suppress noise to ensure the stability of laser,a birefringence filter was placed in the cavity due to balancing nonlinear filtering effect,we achieved the stable ultrashort pulse laser output.Then,we realized the ultrashort pulse of output average power greater than 139 mW,28.1 MHz repetition frequency rate,pulse width 3.8 ps,and center wavelength of 1028 nm with 3 dB ultrashort pulse spectrum bandwidth of 13.8 nm at 500 mW pump power.Considering the long length of single mode fiber can effectively enhance the Raman scattering effect in the cavity,thus we can realize the wide output spectrum of laser.So on the basis of stable mode locking,we study wide spectrum mode-locked laser by increasing the single-mode fiber length and removing the birefringent filter.In the experiments,we obtain stable mode locked ultrashort pulse with the maximum output average power of 90 mW,the repetition frequency of 3.58 MHz,the pulse width of 519 ps,and the output wavelength of 1005-1140 nm.Finally,based on the spectral tunable characteristics of the Sagnac loop mirror,we realized the 1 ?m.wavelength tunable ultrashort pulse by adjusting the polarization controller,which repetition frequency rate is 18 MHz,the pulse width is less than 11.4 ps and the center wavelength is 1035 nm of tunable range up to 15 nm.