Generating 1.2 GHz, 38 fs stretched-pulse directly from a robust mode locked solid-state fiber laser

We demonstrated what is believed to be the first 1.2 GHz nonlinear polarization rotation stretched-pulse mode-locked Yb:fiber laser with a compact design and innovative components. With a compact Faraday rotation angle has been used in NPR mode-locked lasers, and we find that incomplete isolation of backward-propagating light does not hinder self-starting. This laser directly outputs sub-40 fs pulses with a spectral bandwidth exceeding 70 nm, achieving over 1 W of average output power. The laser serves as a seed source, generating a supercontinuum over one octave-spanning range without external amplification or compression.