GHz Fundamental Repetition-rate Picosecond Ytterbium-doped All-fiber Laser

Fiber laser has wide application prospect in industrial,medical and military fields because of their essential characteristics such as high conversion efficiency,excellent beam quality,good thermal diffusivity and compact configuration.High repetition frequency ultra-short pulse fiber laser has been widely used in optical fiber communication,astronomical optical comb,ultrafast optical imaging and material processing and other fields.In this paper,high repetition rate passive mode locking Ybdoped fiber lasers are systematically reported,and the ultra-short pulse Yb-doped fiber lasers with ultra-short cavities are simulated in the software Fiberdesk.The experimental studies on the core amplification characteristics of GHz repetition rate picosecond pulse laser are carried out.The main subjects are as following:(1)The basic theory involved in the mode-locked fiber laser is discussed and studied.Firstly,the mechanism of dispersion,nonlinearity and gain characteristics in the fiber and its influence on the characteristics of the mode-locked pulse are explored.Secondly,the Ginzburg-Landau equation is deduced from the Maxwell equations.The equation is a numerical simulation of the fiber laser.Finally,split-step Fourier method for numerical solution is briefly introduced.(2)Through the experimental study on the picosecond pulse ytterbium doped fiber laser with a Semiconductor Saturable Absorber Mirror,a high repetition rate pulse laser output is obtained by using the method of shortening the cavity length.In a linear resonator with a length of about 3.2 cm,a stable continuous mode locking pulse output with an average power of 8.7 mW is achieved when the pump power is 250 mW.The basic repetition rate of 3.1 GHz,pulse width is 30 ps,the center wavelength is 1064.3 nm and the 3 dB spectral width is 0.06 nm.A high frequency passive mode-locked ytterbium-doped fiber laser based on ultra-short cavity was used as the seed source,with the repetition frequency of 1 GHz,the pulse width of 38 ps and the spectral width of 0.1 nm.The laser with an average power of 100 mW was obtained through a core amplifier with pulse peak power of 2.63 W and spectral width of 0.12 nm.The slope efficiency of the amplifier was 27.9%.In order to improve the stability of the laser,the all fiber encapsulation experiment are carried out using commercial ceramic ferrule.In addition,the influence of the resonant cavity length on the pulse output characteristics is explored.It is concluded that the pulse width depends mainly on the FBG filter bandwidth,and the pulse width will vary with the dispersion value in the cavity.(3)In order to understand the fiber lasers more intuitive and profound,a reasonable numerical model is established for the passive mode locking ytterbium doped fiber laser with ultra-short cavity in the experiment with the pulse transmission theory in optical fiber,and simulated by using Fiberdesk software.In the software,the influence of the parameters such as the modulation depth and the saturation fluence of the SESAM,the FBG filter bandwidth on the output characteristics of the laser is investigated by changing the parameter setting of the device in the cavity.The output pulse width of the laser will decrease with the increase of the modulation depth of SESAM and increase with the saturation flux of SESAM.It will decrease with the increase of FBG filter bandwidth in a certain range,and will be stable after decreasing to a certain level.And the impact of the FBG bandwidth effects on pulse output characteristics is much larger than other parameters.