  A pulsed regime of short-cavity, heavily erbium-doped fiber lasers is of high
interest for its possible applications in telecommunications and sensorics.
Here, we demonstrate these lasers in two configurations, distributed feedback
laser and compare it with a classic Fabry-Perot type laser. We have managed to
create lasers that function stably with cavities as small as 50 mm. Pulse
properties such as amplitude, frequency and duration, are in a good agreement
with our theoretical analysis, which takes into account spontaneous emission.
We report the observation of the thermal switching effect, which consists of
the pulsing regime changing to CW upon cooling the laser cavities down to the
liq-uid nitrogen temperature. We theoretically show that this effect may be
explained by weakening of the up-conversion process responsible for the pulsed
regime. The slowing of the up-conversion processes is due to the energy
mismatch in this process, which is overcome by interaction with phonons. At low
temperatures, the number of phonons decreas-es and pulsing switches off.
