1.61 μm high-order passive harmonic mode locking in a fiber laser based on graphene saturable absorber

We demonstrate a passive mode-locked Er:Yb doped double-clad ring fiber laser based on graphene saturable absorber. By adjusting the polarization controller and minimizing the cavity loss, the laser can operate at hundreds of harmonics of the fundamental repetition frequency of the resonator with the central wavelength of 1.61 μm. Up to 683rd harmonic (which corresponds to 5.882 GHz) of the fundamental repetition frequency was achieved.