Research On Ultrashort-pulse Fiber Laser Based On Nonlinear Amplifying Ring Mirror

Compared with the traditional solid laser,fiber laser has the advantages such as low cost,compact structure,good heat dissipation and high stability etc.At the same time,the ultrashort pulse fiber laser with narrow pulse width,high peak power and spectrum width is widely used in the field of application such as precision spectroscopy and ultrafast microscopy.Therefore,how to obtain the fiber laser with ultrashort pulse has become One of the hottest researches around the world.At present,the main way of obtaining ultrashort pulses including Q-switching technology and mode locking technology,but Q-switching technology is limited by the modulation devices,it is difficult to obtain the femtosecond mode-locked pulse,currently the most widely technology used is the mode locking technology,including active mode locking,self-mode locking and passive mode locking etc.The first two kinds of mode-locked technology are greatly influenced by external environment and have poor stability.Passive mode-locked technology uses nonlinear effect to realize mode locking and has the advantages of simple structure.It has become the mainstream mode locking technology of fiber lasers.However,in the passive mode locking technology reported now,saturable absorber laser is limited by the limitation of the device itself and Its service life is short.There is free space in the laser based on nonlinear polarization rotation laser,which has poor ability to environment.In particular,the cavity based on figure-of-9 fiber oscillators have caused widespread concern due to environmental stable operation.However,most of the reported designs included free space section in the cavity of the laser,which made them less compact and alignment sensitive.In this paper,we develop an all polarization-maintaining(PM)and all-fiber oscillator with a compact custom-designed phase shifter,and self-starting operation is achieved.The main research work of this paper and the results obtained are as follows:1.Based on mode-locked principle of nonlinear optical loop mirror,the principle of fiber laser with figure-eight cavity is derived.2.Under the guidance of theory,the passive mode-locked fiber laser based on figure-eight cavity is built.The output pulse duration can be compressed down to femtosecond,nearly transform-limited.3.We improved the structure of figure-eight cavity by opening the sub ring,shortening the length of the cavity and increasing the repetition frequency.We verified the new cavity structure based on figure-nine cavity in the experimental environment,and finally obtain all-fiber,all-PM and self-starting ultrafast fiber laser.4.We further verify the influence of various parameters of the mode-locked device in figure-nine cavity,including the size of the phase shifter,the splitting ratio of the coupler,the length of the single-mode fiber and so on,and obtain the mode locked laser with a repetition rate of 96MHz and pulse width of 421 fs.