Generating 84 fs, 4 nJ directly from an Yb-doped fiber oscillator by optimization of the net dispersion

We reported a simple and compact Yb-doped fiber femtosecond oscillator, which is based on a dispersion management and nonlinear polarization evolution (NPE) technique. Here, 84 fs, 4 nJ at 1030 nm pulses were generated directly from the mode-locked fiber oscillator by optimization of the net dispersion of the cavity. Only a pair of gratings was used to compensate the positive dispersion caused by the fibers and other optics in the cavity. This is, to our knowledge, the shortest pulse duration directly from a fiber oscillator without any extra compressor outside the cavity. (paper)