D. E. Edmundson and R. H. Enns, "Bistable light bullets," Optics Letters. 17, 586 (1992).

The robust (soliton-like) nature of bistable light bullets is demonstrated numerically for some illustrative models through three-dimensional switching simulations and collision studies. Bistable light bullets are propagating, spheroidal, bright optical solitons characterized by different sizes and intensity profiles but with the same energy.