Theoretical Study Of Dispersion-managed Passively Mode-locked Thulium-doped Fiber Lasers

2?m passively mode-locked fiber lasers have widespread applications in optic communication,spectroscopy,medicine,and military fields,due to their excellent beam quality,compactness,and ultra-high peak power.At the wavelength region of 2?m,silica fibers exhibit large negative dispersion,leading to a soliton operation of thulium fiber lasers without dispersion compensation which have been demonstrated by different mode-locking schemes.Alternatively,elements for dispersion compensation can be implement into the cavity,enabling the laser to operate in the stretched-pulse regimes,especially noramal dispersion regimes,which allow for relatively high pulse energies compared to the fundamental soliton regime.Moreover,the pulse-shaping dynamics and pulse output characteristics of these fiber lasers are different from conventional fiber lasers with soliton operation.Therefore,systemically study the pulse evolution dynamics and output properties of the stretched-pulse mode-locked fiber lasers would contribute to improve the performance of lasers and deepen people's understanding of high energy ultrafast passively mode-locked thulium doped fiber lasers.In this paper,the intracavity pulse evolution dynamics and output properties of a thulium doped mode-locked fiber laser we investigated numerically.The main results are summarized as follows.1.Based on all negative dispersion scheme,stable single soliton operation and multi-soliton operation were obtained.The output single pulse which is nearly transform-limited pulse has the width of 1.99 ps.Moreover,the soliton was characterized by polarization rotation vector soliton.Besides,a wavelength tunable soliton spectrum was achieved easily in the case of stable single soliton operation by tuning the intracavity fiber birefringence.Numerical simulation results show that,using a longer SMF can suppress spectral sideband.2.The energy exchange between strong and weak polarization component was vertified in a dispersion-managed negative thulium doped passively mode-locked fiber laser.The simulation results show that the modulation of SA and strong fiber birefringence effect dramatically influence the properties of the thulium doped dispersion management negative dispersion fiber laser.3.The characteristics of intracavity pulse evolution of dispersion-managed normal dispersion passively mode-locked thulium doped fiber laser was investigated numerically.A stable dissipative soliton pulse output was achieved at the net cavity dispersion of 0.001 ps2 and the output single pulse energy is approaching to 20 nJ.Numerical simulation results show that,the modulation depth and saturation power of saturable absorber play an important role in generating high energy ultrafast pulse.