An all-optical event horizon in an optical analogue of a Laval nozzle
  Exploiting the fact that light propagation in defocusing nonlinear media can mimic the transonic flow of an equivalent fluid, we demonstrate experimentally the formation of an all-optical event horizon in a waveguide structure akin to a hydrodynamic Laval nozzle. The analogue event horizon, which forms at the nozzle throat is suggested as a novel platform for analogous gravity experiments. 
Moshe Elazar, Victor Fleurov and Shimshon Bar-Ad
physics.optics