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.
We present a review of the development of a compact and high-power broadband terahertz （THz） source optically excited by a femtosecond photonic crystal fiber （PCF） amplifier.The large mode area of the PCF and the stretcher-free configuration make the pump source compact and very efficient.Broadband THz pulses of 150 μW extending from 0.1 to 3.5 THz are generated from a 3-mm-thick GaP crystal through optical rectification of 12-W pump pulses with duration of 66 fs and a repetition rate of 52 MHz.A strong saturation effect is observed,which is attributed to pump pulse absorption;a Z-scan measurement shows that three-photon absorption dominates the nonlinear absorption when the crystal is pumped by femtosecond pulses at 1 040 nm.A further scale-up of the THz source power is expected to find important applications in THz nonlinear optics and nonlinear THz spectroscopy.
