Reflections from a fiber positioned at a very short distance from the
output facet of a DFB laser diode are shown to induce variations of bo
th mean turn-on time and time jitter under gain switching. Their measu
red values strongly depend on the phase of the reinjected field even f
or very small feedback levels. A simple model based on the coupled rat
e equations for photon and carrier populations is able to describe the
experimental results.