Manipulation,Characterization And Amplification Of Specific Ultrashort Pulse From Passively Mode-locked Fiber Lasers

Fiber lasers are ideal ultrashort pulse sources due to its inexpensive components,high integration and convenient collimation,which have greatly promoted the developments and applications of the ultrafast optics.This paper mainly investigated the manipulation,characterization and amplification of the specific ultrashort pulse from passively mode-locked fiber lasers by means of numerical simulations and experiments.The mainly research works are listed as follows:1.Manipulation of group-velocity-locked vector solitons(GVLVSs)from fiber lasers is numerically proposed and experimentally demonstrated.High-order vector solitons could be generated from a fundamental GVLVS with the help of a polarization controller(PC)and a polarization beam splitter(PBS).Specifically,a high-order vector soliton with a two-humped pulse along the one polarization could be obtained.The spectral interference between the two humps leads to the strong dip at the center of the spectrum,which indicates that the phase difference between the two humps is 180°.Although the orthogonally polarized pulses after the PBS actually did not lock together,the optical spectra of the projections along the two axis are same to those of a high-order GVLVS,as well as the intensity profile.Therefore,we name it as “pseudo-high-order GVLVS.”2.Based on a Michelson interferometer,a beam splitter splits an incoming pulse into two pulses,which are then focused and sent into a crystal for the second-harmonic generation,which provides a usual pulse width characterization for the ultrashort pulse.In this paper,the autocorrelation measurements of the noise-like pulses(NLPs)from fiber lasers are investigated using numerical analysis.Numerical analyses show that the intrinsic low coherence of the NLPs together with the scan range limitation lead to the contrast ratio of the interferometric autocorrelation trace of the NLPs less than 8:1.3.High peak power picosecond pulses are needed for a variety of applications,such as micromachining.In some cases the amplified pulses should be close to the transform limit.Divided-pulse amplification(DPA)is a totally new method,which is different from the conventional methods,to generate picosecond pulses with high peak power and energy.The DPA with four-birefringent-crystal stack and a large mode area fiber is investigated numerically.The criteria to obtain picosecond pulses with 10 MW peak power before the pulses become significantly distorted are confirmed.