(Top) Experimental configuration used by Minardi et al. to produce light bullets. 1550-nm laser pulses with 170-fs duration go into a hexagonal array of glass waveguides. The nonlinear optical interaction in the glass causes formation of solitons that are stable in time and space. Part of the original laser beam is split off and is used to map out the pulse shape. (Bottom) Upper panel shows how a pulse undergoes spreading in time during propagation in the waveguide array. Lower panel shows how nonlinear effects cause the light packet to remain stable and compact as it moves.