Optical event horizons from the collision of a soliton and its own dispersive wave

We observe experimentally the spectral signature of the collision between a soliton and the dispersive wave initially emitted from the soliton itself. This collision, interpreted in terms of an optical event horizon, is controlled by the use of an axially varying fiber which allows us to shape both the soliton and dispersive wave trajectories so that they both collide at a precise location within the fiber. The interaction of the dispersive wave with the soliton generates a reflected wave with a conversion efficiency which can be controlled by the input pump power. These experimental results are confirmed by numerical solution of the generalized nonlinear Schrodinger equation and by the analytical calculation of the conversion efficiency.