Passive harmonic mode locked all-normal-dispersion Yb-doped fibre lasers

Passive harmonic mode-locking of dissipative solitons is demonstrated in all-normal dispersion Yb-doped fibre lasers. A difference equation model of the mode-locked fibre lasers is adopted to simulate the intra-cavity nonlinear dynamics. Hysteresis phenomena around the mode-locking threshold, and the effect of introducing linear phase bias are discussed. The passive harmonic mode-locking as one kind of multipulsing operations is revealed. Moreover, the simulation shows the bistability between multipulsing and single-pulse or period multiplication.