Graphene Mode-Locked Fiber Laser at 2.8 $\mu \text{m}$

Mid-infrared erbium (Er
³⁺
)-doped ZrF
₄
-BaF
₂
-LaF
₃
-AlF
₃
-NaF fiber laser mode-locked by multilayer graphene saturable absorber was demonstrated. Mode-locked pulses at 2.8 μm with an average output power of 18 mW at a repetition rate of 25.4 MHz, corresponding to a pulse energy of 0.7 nJ, were obtained. The pulsewidth was measured to be ~42 ps by a home-made autocorrelator. Our experiment has validated the mode-locking capability of graphene in the 3-μm wavelength region.