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
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.
