Passive harmonically mode-locked fiber laser with low pumping power based on a graphene saturable absorber

A passive harmonically mode-locked fiber laser based on a graphene saturable absorber has been experimentally demonstrated. Under different pump powers and different polarization states of the cavity, lower and higher order harmonic mode-locking has been obtained. The 46th scalable harmonic was achieved which corresponded to a repetition rate of 0.49 GHz and could be observed at a relative lower pump power of 162.4 mW. We deduce that the existence, position and stability of the relatively strong continuous wave components in the spectrum of solitons play an important role in the formation of higher order harmonic mode-locking.