Generating ultrafast pulses by direct amplification in short, heavily doped phosphate-glass fiber

A simple alternative, which utilizes direct amplification of ultrashort pulses in a short and heavily-doped active fiber made of soft phosphate glass, is presented. The amplification was so rapid that no significant pulse distortion occurred in either the temporal or spectral domain. Both oscillator and amplifier stages utilize short pieces of side-pumped phosphate fiber as gain elements. The core of the single-mode active fiber is heavily co-doped with Er and Yb ions. The short-pulse operation of the oscillator is initiated by the semiconductor saturable absorber mirror (SESAM), which serves as one of the reflectors in the standing-wave laser cavity. Further power up-scaling is possible by using a large-mode area fiber in the amplifier stage.