Solitons supported by a self-defocusing trap in a fractional-diffraction waveguide

We introduce a model which gives rise to self-trapping of fundamental and higher-order localized states in a one-dimensional nonlinear Schrödinger equation with fractional diffraction and the strength of the self-defocusing nonlinearity growing steeply enough from the center to periphery. The model can be implemented in a planar optical waveguide. Stability regions are identified for the fundamental and dipole (single-node) states in the plane of the Lévy index and the total power (norm), while states of higher orders are unstable. Evolution of unstable states is investigated too, leading to spontaneous conversion towards stable modes with fewer node.