Dark (b) 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 mum 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.
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"Only a year later Duree et al.  were able to observe them experimentally. Till date, theoretical as well as experimental investigations have been made on different types of PR spatial solitons of which screening solitons (SS)     , photovoltaic (PV) solitons   and screening photovoltaic (SP) solitons   , being the most widely and thoroughly investigated categories. These solitons have been found to exist in bright, dark and grey, scalar as well as vector configurations . "
[Show abstract][Hide abstract] ABSTRACT: This paper presents an investigation on the propagation characteristics of optical spatial solitons in a biased centro-symmetric photorefractive medium. Unlike earlier attempts on photorefractive solitons, in the present investigation, we have given equal significance to the effects of charge drift and their diffusion. We have obtained dynamical equations for solitons employing paraxial ray approximation and examined criteria for stationary propagation. Trajectories of stationary solitons have been examined.
"One of the physical mechanisms that supports the existence of spatial solitons in photorefractive media is the self-phase modulation self-focusing, which originates from intensity-dependent modulation of the refractive index. Based on this mechanism, several types of photorefractive spatial solitons have been investigated, i.e., quasi-steady-state solitons  , screening solitons   , photovoltaic solitons    , screening-photovoltaic solitons   , and self-trapping of incoherent beams   or white light beams  . Cohen et al.  proposed a new kind of optical spatial solitons and named them as holographic solitons, for they rely solely on holographic focusing. "
[Show abstract][Hide abstract] ABSTRACT: It is shown theoretically that the signal beam alone can evolve into steady-state bright and dark holographic solitons in a centrosymmetric photorefractive dissipative system that includes two balances, i.e., loss is exactly compensated by gain and diffraction is compensated by nonlinearity resulting from both self-phase modulation self-focusing and holographic focusing. These solitons have fixed amplitude and width. When the absorption of the system is neglected and the pump beam is switched to a background light, these solitons can become the “traditional” photorefractive solitons with arbitrary amplitude.
Full-text · Article · Jun 2010 · Optics and Lasers in Engineering
"During the last decade, the optical spatial solitons based on photorefractive effect have attracted much interest, for these photorefractive spatial solitons can be formed at low light intensity and are potentially useful for all-optical switching, beam steering, and optical interconnects. At present, three types of steady-state scalar solitons (screening solitons   , photovoltaic solitons     and screening-photovoltaic solitons   ) have been predicted theoretically and found experimentally. The diffusion process introduces an asymmetric tilt in the light-induced photorefractive waveguide, which results in the self-deflection process of solitons . "
[Show abstract][Hide abstract] ABSTRACT: We investigate the effects of higher-order space charge field on the self-deflection of bright screening spatial solitons due to two-photon photorefractive effects by a numerical method under steady-state conditions. The expression for an induced space charge electric field including higher-order space charge field terms is obtained. Numerical results indicate that bright screening solitons undergo self-deflection process during propagation, and the solitons always bend in the opposite direction of the c axis of the crystal. The self-deflection of bright screening solitons can experience considerable increase especially in the regime of high bias field strengths. Relevant examples are provided.