Research On Techniques Of Saturable Absorber 1.5?m Dissipative Soliton Mode-locked Fiber Laser

Ultra-short pulse fiber laser has been widely applied to laser processing,defense weapons,optical fiber sensing,medical and laser radar due to its advantages of beam quality,good heat dissipation,no need of collimation,good compact structure and high conversion efficiency.The high-energy ultrashort pulse is more valuable in practical application.The main method to realize the ultra-short pulse laser is passive mode locking.In fiber laser,comparing with others types solitons,dissipative soliton can overcome the energy limitation of traditional soliton pulse.In this paper,the nonlinear phase shift accumulation of dissipative solitons is reduced,and the mode-locking pulse of dissipative solitons by bismuth telluride saturable absorber is achieved.The research contents of this paper mainly include:1.The process of laser mode-locking is studied in detail,and the mode-locking pulse can realize ultrashort pulse.The effects of dispersion and nonlinear effects on the time and frequency domains of optical pulses are analyzed in detail.We introduced four kinds solitons based on different physical mechanisms which are traditional solitons,dispersion managed solitons,self-similar solitons and dissipative and analyzed their feature.We finally determined scheme of dissipative solitons after theoretical analysis.2.We analyzed the influence of fiber nonlinearity and dispersion effect on dissipative solitons in ring cavity and explored the method that reduces the nonlinear phase shift of dissipative solitons and increases pulse energy and peak power.Firstly,we established modelocked fiber laser model and we simulated the dissipative soliton fiber laser using the software of Rp fiber power,Then we analyzed the total nonlinear phase shift in the cavity with B-integral.We applied a new method that optimized the distribution of the passive fiber without adding other optical element to reduce the total nonlinear phase shift in the cavity and increase the pulse output energy.that optimized the distribution of the passive fiber in the cavity to reduce the total nonlinear phase shift and increase the pulse output energy.Finally,we added large mode field negative dispersion fiber to balance the linear chirp of the output pulse that increased the peak power of the fiber laser output and compressed the pulse width.3.We analyzed the influence of the optical properties of saturable absorber on the mode locking.Finally,we selected the bismuth telluride as the saturable absorber.We synthesized high-quality bismuth telluride nanosheets by hydrothermal synthesis method and made "sandwich" structure saturable absorber.We studied the linear and nonlinear saturable absorption characteristics of bismuth telluride.We built mode-locked fiber laser and achieved rich experimental phenomena such as traditional soliton mode-locked and dissipative soliton mode-locked fiber laser.At 400 mW of pump power,the pulse output with a repetition frequency of 15 MHz,a pulse width of 180 ps and a spectrum width of 4.6 nm was achieved.At 593 mW of pumping power,the average output power was 12.7 mW.