Propagation and stability of optical pulses in a diffractive dispersive non-linear medium

Propagation and stability of light pulses under the combined influence of the optical Kerr effect, dispersion and diffraction are investigated by adopting a variational procedure. In particular, it is found that 'light bullets', i.e. radially symmetric pulses propagating without distortion, are not necessarily unstable under perturbations which do not maintain radial symmetry.