Self-trapping of dark incoherent light beams

Abstract

Thus far, dark solitons have been studied using spatially-coherent light beams only. However, nature is full of incoherent light as well as coherent light. In fact, many sources of electromagnetic radiation emit spatially incoherent light. Recently, our group has demonstrated that bright beams from a spatially incoherent light source can form incoherent solitons in non-instantaneous nonlinear media [1,2]. Can such incoherent beams support dark solitons? Here we report the first experimental observation of self-trapping of spatially-incoherent dark beams in the form of one-dimensional dark stripes and of two-dimensional dark vortices. Self-trapping of dark incoherent beams, or, in a broader sense, self-trapping of dark incoherent wave-packets, is a fundamentally new concept. Even though we have shown previously that bright incoherent beams can self-trap in a nonlinear medium [3-5], the extension to dark beams (or voids borne on the background of incoherent beams that are otherwise uniform in space) is far from being obvious. From the applications view-point, since in general self-trapped beams (bright and dark, coherent and incoherent) induce waveguides in the volume of a bulk nonlinear medium, our experiments offer a unique possibility of controlling incoherent light with incoherent light, or, even more surprising, controlling coherent light with incoherent light. This means that light which originates from Light Emitting Diodes (LEDs), which is spatially-incoherent, can be used to guide, steer and control laser beams.