50 fs pulses from an all-normal dispersion erbium fiber oscillator.

We present a mode-locked, all-normal-dispersion erbium-doped fiber oscillator generating output pulses with broadband spectra covering the range from 1475 to 1620 nm. The oscillator operates at a repetition rate of 109 MHz with output pulse energies of 1.6 nJ. Mode-locked operation is achieved by use of nonlinear polarization evolution in combination with a birefringent filter. The output pulses are dechirped with an external prism compressor to a duration of 50 fs.