Evidence of 1+1D Photorefractive Stripe Solitons Deep in the Kerr Limit

The Kerr nonlinearity allows for exact analytic soliton solutions in 1+1⁢D. While nothing excludes that these solitons form in naturally occurring real-world 3D settings as solitary walls or stripes, their observation had previously been considered unfeasible because of the strong transverse instability intrinsic to the extended nonlinear perturbation. We report the observation of solitons that are fully compatible with the 1+1⁢D Kerr paradigm limit hosted in a 2+1⁢D system. The waves are stripe spatial solitons in bulk copper doped potassium-lithium-tantalate-niobate (KLTN) supported by unsaturated photorefractive screening nonlinearity. The parameters of the stripe solitons fit well, in the whole existence domain, with the 1+1⁢D existence curve that we derive for the first time in closed form starting from the saturable model of propagation. Transverse instability, that accompanies the solitons embedded in the 3D system, is found to have a gain length much longer than the crystal. Findings establish our system as a versatile platform for investigating exact soliton solutions in bulk settings and in exploring the role of dimensionality at the transition from integrable to nonintegrable regimes of propagation.