Waveguides and directional coupler induced by white-light photovoltaic dark spatial solitons

We have observed experimentally, for the first time to our knowledge, one-dimensional photovoltaic dark spatial solitons in LiNbO3:Fe crystal by using incoherent white light. We have also fabricated a directional coupler consisting of two waveguides induced by two mutually incoherent white-light photovoltaic dark spatial solitons propagating in parallel in close proximity. It was found that the light field of a probe laser beam launched into one of the two proximate waveguides can be efficiently coupled into the other waveguide because of the presence of evanescent waves. We also studied the dependence of the coupling efficiency on the distance between the two proximate soliton-induced waveguides. (C) 2004 Optical Society of America.