Dark and bright photovoltaic spatial solitons

Dark (bright) planar spatial solitons are predicted for photovoltaic photorefractive materials when the diffraction of an optical beam is exactly compensated by nonlinear self-defocusing (focusing) due to the photovoltaic field and electro-optic effect. These solitons may have steady-state irradiances of microwatts to milliwatts per square centimeter and widths as small as 10 \ensuremath{\mu}m in lithium niobate. Optical control is provided by incoherent illumination, and the nonlinear index of a dark soliton may be used to trap a bright soliton by rotating the plane of polarization of the soliton field.