Optical pulses at a repetition rate of 39.8 GHz have been
observed in a dc-biased passively mode-locked quantum-dash Fabry-Perot ´
laser diode. The pulses generated by this diode are studied in the temporal
and spectral domains using a second harmonic generation frequency-resolved optical gating system. By using a tunable band-pass filter, it is
observed that the pulse width decreases as the number of lasing modes
selected by the filter increases. Furthermore, by controlling the phase
difference of the modes using a 450m-long single mode fibre, a passive
compression of the pulses is obtained. A minimum pulse width of 720 fs
has been measured with this type of mode-locked Fabry-Perot laser.