Passive harmonic mode locking in erbium-doped fiber laser with graphene saturable absorber

We report passive harmonic mode-locking of a soliton erbium-doped fiber laser based on graphene saturable absorber. 32nd harmonic of the fundamental cavity frequency has been obtained with pulse duration 950 fs. The repetition rates are continuously scalable from 15.71 to 502.84 MHz. The cavity supermode is suppressed up to 50 dB, and the signal-to-noise ratio is better than 67 dB at the 32nd harmonic.