Dispersion-compensation-free femtosecond Tm-doped all-fiber laser with a 248 MHz repetition rate.

In this Letter, we report a dispersion-compensation-free ultrafast thulium-doped all-fiber laser based on nonlinear polarization evolution (NPE) mode locking, delivering 330 fs soliton pulses at 1950 nm. A multifunctional hybrid fiberized device was applied in the oscillator to minimize the physical cavity length to ∼80  cm with a total dispersion of -0.045  ps², enabling a state-of-the-art fundamental mode-locking repetition rate of 248 MHz in an NPE-based oscillator at ∼2  μm.