Steady-state multiple dark photovoltaic spatial solitons

We theoretically study the formation of the steady state multiple dark photovoltaic spatial solitons in the photovoltaic photorefractive crystal under open-circuit conditions. The results indicate that the initial dark notch width at the entrance face of the crystal is a key parameter for generating an even (or odd) number sequence of multiple dark photovoltaic solitons. The dark notch is generated from a phase or amplitude discontinuity in the center of the input beam. If the initial width of the dark notch is small, only a fundamental soliton or a Y-junction soliton is generated. As the initial width of the dark notch is increased, the dark notch tends to split into an odd (or even) number of multiple dark photovoltaic solitons, realizing a progressive transition from a lower-order soliton to the higher-order multiple solitons. When the multiple dark photovoltaic solitons are generated, the separations between adjacent dark solitons become smaller. Solitons pairs become progressively wider and less visible as their transverse distance from the central dark soliton increases and they move away from each other as they propagate in the photorefractive nonlinear crystal.