Picosecond pulses from a neodymium-doped fiber laser mode-locked with a linear external cavity

The lasing characteristics of a neodymium-doped silica fiber laser mode-locked with a linear external cavity with vibrating mirror are measured. The investigation of the dependence of the duration of the laser pulses on the mismatch between the lengths of laser resonator and external cavity shows that mode-locking is impossible if both cavities are exactly matched. The shortest pulses have a duration less than 32 ps. A simple analytical and numerical study gives insight in the physical mechanism underlying this interesting mode-locking technique.