The expression for an induced space-charge electric field, including higher-order space-charge field terms, in biased photovoltaic-photorefractive crystals is obtained. There are two higher-order odd perturbation terms in the expression, and their signs depend on the polarity of the bias and the photovoltaic fields, respectively. The effects of the higher-order terms on self-deflection of screening photovoltaic bright solitons in the crystals are investigated by both numerical and perturbation methods under steady-state conditions. When the bias field is positive and the photovoltaic field is negative, the screening photovoltaic bright solitons always bend in the direction opposite the crystal's c axis, and the absolute value of the spatial shift that is due to the first-order diffusion term alone is always smaller than that which is due to the first-order diffusion term and the higher-order terms together. When the bias field is negative and the photovoltaic field is positive or the two fields are both positive, bending in both the same direction as and in the direction opposite the crystal's c axis is possible. Whether the direction is in the same or in the opposite direction will depend on the polarity and strength of the two fields and on the incident optical intensity; it is possible that no self-deflection will occur if the strength and polarity of the two fields and the incident intensity are appropriately selected. Relevant examples are provided. (C) 2002 Optical Society of America. [References: 18]
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