A stable nonlinear wave packet, self-localized in all three dimensions, is an
intriguing and much sought after object in nonlinear science in general and in
nonlinear photonics in particular. We report on the experimental observation of
mode-locked spatial laser solitons in a vertical-cavity surface-emitting laser
with frequency-selective feedback from an external cavity. These spontaneously
emerging and long-term stable spatio-temporal structures have a pulse length
shorter than the cavity round trip time and may pave the way to completely
independent cavity light bullets