  We present an experimental and theoretical study of an unusual bursting
mechanism in a two-mode semiconductor laser with single-mode optical injection.
By tuning the strength and frequency of the injected light we find a transition
from purely single-mode intensity oscillations to bursting in the intensity of
the uninjected mode. We explain this phenomenon on the basis of a simple
two-dimensional dynamical system, and show that the bursting in our experiment
is organised by a cusp-pitchfork bifurcation of limit cycles.
