Ultrafast Dy ³⁺ :Fluoride fiber laser beyond 3 µm

We report a passively mode-locked Dy :fluoride fiber laser emitting around 3.1 ?m based on the nonlinear polarization evolution technique in a ring configuration, using in-band pumping at 2.8 ?m. Transform-limited and self-starting mode-locked pulses as short as 828 fs with a center wavelength around 3.1 ?m and repetition rates up to 60 MHz are obtained. In the single-pulse regime, a maximum average output power of 204 mW is measured, corresponding to a peak power of 4.2 kW and a pulse energy of 4.8 nJ. This first demonstration, to the best of our knowledge, of a femtosecond mode-locked fiber laser emitting directly beyond 3 ?m paves the way for frequency comb synthesis in the molecular fingerprint region.