One-dimensional steady-state spatial solitons in photovoltaic photorefractive materials with an external applied field

A theory on spatial solitons in closed-circuit photorefractive-photovoltaic media is developed that gives rise to spatial solitons due to both the bulk photovoltaic effect and the spatially nonuniform screening of the external bias field. In case the photovoltaic effect can be neglected, these solitons are screening solitons. In case the external bias field is absent, these solitons are photovoltaic solitons in the closed-circuit case. We also show theoretically that the photovoltaic nonlinearity can be switched from self-defocusing to self-focusing by adding the external electric field. Under a strong bias condition, the photovoltaic nonlinearity can be switched from self-defocusing to self-focusing by changing the polarity of the external electric field or by rotating the polarization of the light.