Sequential formation of multiple dark photorefractive spatial solitons: experiments and theory

Steady-state dark photorefractive spatial screening solitons are observed in an odd- or even-number sequence when a laser beam that contains a dark stripe generated from a phase or amplitude discontinuity in the center of the beam is launched into a biased bulk strontium barium niobate crystal. If the initial width of the dark stripe is small, only a fundamental soliton or a Y-junction soliton is generated, corresponding to the lowest order in the odd- or even-number soliton sequence. As the initial width and the bias field are increased, we observe a progressive transition from a lower-order soliton to a sequence of higher-order multiple solitons. We show that these dark solitons induce stable waveguides that can guide an intense beam of a different wavelength into multiple channels. Comparisons between experiments and theory on multiple dark spatial solitons are presented and shown to be in good agreement.