Ytterbium fiber laser producing 89-fs pulses directly at the fiber output

In this paper, a laser that delivers sub-100 fs chirp-free pulses directly at the fiber output is demonstrated. The cavity is optimized to supply both large optical spectrum and negative chirp at the input of the output fiber lead. The laser gain medium is 16-cm highly doped ytterbium-doped fiber. The ytterbium-doped fiber is pumped with via a dichroic fiber coupler by a 980 nm laser diode delivering up to 300 mW. Dispersion compensation is provided by a pair of 1250-lines/mm transmission gratings with separation of 4 mm. Self-starting mode-locked operation was initiated through the use of a semiconductor saturable absorber mirror. It is concluded that this is the shortest pulse obtained from an ytterbium fiber laser without external dispersion compression by bulk gratings.