Time- and frequency-domain theory of externally synchronised operation of a passively mode-locked laser diode
calculations, based on a third order approximation for the chirp, show that the third order chirp coefficient, which can be evaluated from A& and higher order moments of the spectrum, is negligible, at least in the present experiment. This confirms the transform limited quality of the pulse. Possible applications of optimized pulses from gain-switched DFB lasers are all optical demultiplexing and soliton generation in ultrahigh bitrate communications. "CNR-Consiglio Nazionale delle Ricerche, Piazzalc Aldo Mom 7 00185 Roma, Italy