Study On Fiber Laser Mode-locking Technique Based On Saturable Absorber

Ultrashort pulse fiber laser has the characteristics of generating ps/fs level ultrashort pulses,high peak power and low threshold,had became an important research direction of laser technology,widely used in ultrafast optical switch,medical,high-speed optical communication,precision machining and so on.At present,passively mode-locked technology which based on saturable absorber is the main mean to achieve ultrashort pulse output.This paper focused on the research of passively mode-locked ultrashort pulse fiber laser,and explored effective ways to compress the optical pulse width.By modeling and calculating the dynamic equation of mode locked fiber laser,analyzed the influence of the dispersion on the pulse width and the influence of various nonlinear effects on the frequency domain of the mode locked pulse.Through the analysised of saturable absorber’s nonlinear optical absorption characteristics on the effect of mode-locked pulse width,used double saturable absorber to improve the modulation depth to compress pulse width,designed transmission /reflection composite double absorber passively mode-locked ultrashort pulse fiber laser and double reflective saturable absorber passively mode-locked ultrashort pulse fiber laser,then simulation.we used graphene and SESAM as saturable absorber,which took advantage of graphene’s high damage threshold,ultrafast electron relaxation time and SESAM’s high modulation depth and lower mode-locked threshold which helped to establish mode-locked pulse,explored the preparation conditions of graphene saturable absorber films,and designed composite passively mode-locked ultrashort pulse fiber laser based on graphene and SESAM.Finally,we obtained the ultrashort pulse output with the central wavelength of 1064.41 nm,the pulse width of 117.34 ps,the repetition frequency of 19.5MHz,the 3dB spectral width of 1.2nm,and the pulse energy of 0.12 nJ under the condition of all positive dispersion.