Stable three-dimensional spinning optical solitons supported by   competing quadratic and cubic nonlinearities
  We show that the quadratic interaction of fundamental and second harmonics in a bulk dispersive medium, combined with self-defocusing cubic nonlinearity, give rise to completely localized spatiotemporal solitons (vortex tori) with vorticity s=1. There is no threshold necessary for the existence of these solitons. They are found to be stable against small perturbations if their energy exceeds a certain critical value, so that the stability domain occupies about 10% of the existence region of the solitons. We also demonstrate that the s=1 solitons are stable against very strong perturbations initially added to them. However, on the contrary to spatial vortex solitons in the same model, the spatiotemporal solitons with s=2 are never stable. 
D. Mihalache, D. Mazilu and L.C. Crasovan (Institute of Atomic   Physics, Bucharest, Romania), I. Towers and B. A. Malomed (...