Tunable, High-Order Harmonically Mode-Locked All-Normal-Dispersion Ytterbium Fiber Laser

We report the generation of passively tunable high peak signal-to-noise ratio harmonic mode-locked (HML) all-normal-dispersion Yb-doped fiber laser with a single birefringent filter in a ring cavity configuration. The highest fourth harmonic of the fundamental mode-locked frequency at a repetition rate of 88 MHz is obtained. The pulses are compressed to 627 fs by using an external grating-pair compressor. For the fourth HML output, the peak signal-to-noise ratio of the rf is 73 dB and the average power is as high as 110 mW with the pump power of 500 mW. Soliton bunches which contain multipulses are also observed in the weak mode-locked regime of the HML, and the separation between interpulses in a dissipative soliton bunch can be controlled by adjustment of the waveplates and spectral filter in the cavity.