  In this paper, we analyze the effect of optical feedback on the dynamics of a
passively mode-locked ring laser operating in the regime of temporal localized
structures. This laser system is modeled by a system of delay differential
equations, which include delay terms associated with the laser cavity and the
feedback loop. Using a combination of direct numerical simulations and
path-continuation techniques, we show that the feedback loop creates echos of
the main pulse whose position and size strongly depend on the feedback
parameters. We demonstrate that in the long-cavity regime, these echos can
successively replace the main pulses, which defines their lifetime. This pulse
instability mechanism originates from a global bifurcation of the saddle-node
infinite-period type. In addition, we show that, under the influence of noise,
the stable pulses exhibit forms of behavior characteristic of excitable
systems. Furthermore, for the harmonic solutions consisting of multiple
equispaced pulses per round-trip we show that if the location of the pulses
coincide with the echo of another, the range of stability of these solutions is
increased. Finally, it is shown that around these resonances, branches of
different solutions are connected by period doubling bifurcations.
