Spatiotemporal mode-locking creates great opportunity for pulse energy scaling and nonlinear optics research in fiber. Until now, spatiotemporal mode-locking has only been realized in normal-dispersion dissipative soliton and similariton fiber lasers. In this paper, we demonstrated the first experimental realization of a spatiotemporally mode-locked soliton laser in mid-infrared fluoride fiber with anomalous dispersion. The mode-locked fluoride fiber oscillator directly generated a record pulse energy of 16.1 nJ and peak power of 74.6 kW at 2.8 μm wavelength. This work extends the spatiotemporal mode-locking to soliton fiber lasers and should have a wide interest for the laser community.

We report on a grating-free fiber chirped pulse amplifier (CPA) at 2.8 μm for the first time. The CPA system adopted Er:ZBLAN fiber with large anomalous dispersion as the stretcher and germanium (Ge) rods as the compressor with a compact structure. High-energy picosecond pulses of 2.07 μJ were generated at the repetition rate of 100 kHz. Using highly dispersive Ge rods, the amplified pulses were compressed to 408 fs with a pulse energy of 0.57 μJ, resulting in a peak power of approximately 1.4 MW. A spectral broadening phenomenon in the main amplifier was observed, which was caused by the special gain shape of the Er:ZBLAN fiber amplifier in operation and confirmed by our numerical simulation. This compact fiber CPA system at 2.8 μm will be practical and meaningful for application fields.