Energy Localization Through Bragg Gratings in Quadratic Media for Second Harmonic Generation

Abstract

A nonlinear optical response coupled with feedback mechanisms is able to support optical multistability in various material systems and geometries. In periodically perturbed waveguides such as distributed feedback gratings (DFBG), a Bragg resonance coupling counterpropagating fields can associate with a Kerr or a parametric nonlinearity to give rise to transmissive nonlinear eigenstates within the otherwise propagation-forbidden photonic bandgap [1-5]. These correspond to energy localization states in the form of stationary or slowly travelling when properly excited, they can be viewed as optical bits trapped within the DFBG for shortor long-term storage depending on their propagation speed. Due to the rapidly growing interest in transparent optical networks and all-optical memories, the possibility of stationary localized states or still gap-solitons in DFBGs is an intriguing one. In this paper, after introducing two-color quadratic gap-solitons or gap-simultons in a channel waveguide for frequency doubling, we address the problem of excitation of slowly moving or stationary states in singly (srDFBG) or doubly resonant gratings (drDFBG), showing that the feasibility of read/write all-optical memories is within experimental reach. In a material system with a quadratically