We report on the observation of planar dark spatial solitons due to the bulk photovoltaic effect in lithium niobate, with intensities of the order of 10 W/cm2 and widths of approximately 20 μm. Photovoltaic solitons display a characteristic tensorial dependence on their direction of propagation, on their polarization, and on the orientation of the amplitude profile, with respect to the principal axes of the crystalline medium. The index perturbation associated with a dark soliton persists in the dark, and it can trap and guide a second beam.

• Received 2 December 1994

DOI:https://doi.org/10.1103/PhysRevA.52.3095