Coupling-induced localization in linearly coupled waveguides with spatially modulated nonlinearity

Abstract

We study stationary, spatially localized modes in linearly coupled optical waveguides governed by coupled nonlinear Schrödinger equations with asymmetric defocusing Kerr nonlinearities. A waveguide with spatially inhomogeneous nonlinearity supports self-trapped states, whereas a homogeneous defocusing waveguide cannot localize on its own. We show that linear coupling induces localization in the nonlocalizing guide. Fundamental and excited stationary modes are computed, and their existence, power asymmetry, and stability are analyzed as functions of the coupling strength and nonlinearity. Dynamical simulations reveal stable ground and first excited states, whereas higher-order modes are unstable. These results demonstrate coupling-induced spatial localization in defocusing nonlinear waveguide systems.