Transition between self-focusing and self-defocusing in a nonlocally nonlinear system

Abstract

We reveal the relevance between the nonlocality and the focusing and defocusing states in a nonlocally nonlinear system with a sine-oscillation response function, and predict a phenomenon that the self-focusing--self-defocusing property of the optical beam in the system depends on its degree of nonlocality. The transition from the focusing nonlinearity to the defocusing nonlinearity of the nonlinear refractive index will happen when the degree of nonlocality of the system goes across a critical value, and vice versa. We also discuss the bright soliton in the focusing state and the dark soliton in the defocusing state, respectively, for such a system.