We investigate the effects of a piece of zero-dispersion fiber(ZDF) on the pulse dynamics of a passively mode-locked fiber laser operating in the stretched-pulse regime.Numerical simulation suggests that the proper location and length of ZDF facilitate spectrum broadening and pulse shortening in fiber lasers while maintaining constant net cavity dispersion.A nonlinear polarization evolution mode-locked Er-doped fiber laser with a dispersion map is built based on the simulation.Larger optical spectrum broadening is obtained by inserting a longer ZDF after the active fiber during single-pulse operation,which well agrees with the simulation.
With linearly coupled nonlinear Schrodinger equations,numerical analysis has been performed on the mode locking forming procedure of a fiber laser in the linear cavity configuration.The fiber is Yb-doped multi-core photonic crystal fiber and semiconductor saturable absorber mirror(SESAM) is adopted as the nonlinear transmission element to start mode locking.Because of the noise randomness,initial pulse would be picked out by SESAM in one or more cores which makes the multi-core mode locking quite different from single-core one.The two situations are compared and fully discussed.Mode locking in multi-core photonic crystal fiber laser can be realized only if the couple coefficient between the cores and the temporal overlap between the pulses in different cores are large enough.
FANG XiaoHui HU MingLie LI YanFeng CHAI Lu WANG QingYue
