Modulational instability of multiple-charged optical vortex solitons undersaturation of the nonlinearity

We present a linear analysis and numerical simulations of the instability o f optical vortex solitons (OVSs) of arbitrary topological charge. They show a rich variety of instability scenarios depending on the type of perturbat ion. The saturation of the nonlinearity is shown to be able to slow down th e decay of multiple charged dark beams at an intermediate evolution stage a nd to prevent their ultimate decay into charge-1 OVSs. This concept is expe rimentally verified by the observation of a partial decay of a triple-charg ed OV beam and by comparing this dynamic with the behavior of OV beams of t opological charges m = 1, 2, 3, and 3. [S1063-651X(99)09912-2].