We obtain single-mode picosecond pulses with a tuning range of more th
an 40 nm by self-seeding of a standard gain-switched Fabry-Perot laser
diode. The switch-on behavior is investigated experimentally and nume
rically for the first time. Stable single-mode operation is reached af
ter less-than-or-equal-to 5 round-trips, which shows the potential for
extremely fast wavelength tuning.