Perfectly absorbed and emitted currents by complex potentials in nonlinear media

Abstract

Recently it was demonstrated that the concept of a spectral singularity (SS) can be generalized to waves propagating in nonlinear media, like matter waves or electromagnetic waves in Kerr media. The corresponding solutions represent nonlinear currents sustained by a localized linear complex potential in a nonlinear Schr\"odinger equation. A key feature allowing the nonlinear generalization of a SS is a possibility to reduce a nonlinear current to the linear limit, where a SS has the unambiguous definition. In the meantime, known examples of nonlinear modes bifurcating from linear spectral singularities are few and belong to the specific class of constant-amplitude waves. Here we propose to extend the class of nonlinear SSs by incorporating solutions whose amplitudes are inhomogeneous. We show that the continuation from the linear limit requires a deformation of the complex potential, and this deformation is not unique. Examples include the deformation preserving the gain-and-loss distribution and the deformation preserving geometry of the potential. For the case example of a rectangular potential, we demonstrate that the nonlinear currents can be divided into two types: solutions of the first type bifurcate from the linear spectral singularities, and solutions of the second type cannot be reduced to the linear limit.