All-optical buffers via localization of two-color quadratic gap solitons

Optical gap solitons are a promising approach towards the realization of all-optical buffers and memories in nonlinear waveguides with Bragg resonant gratings [1]. In fact they permit to localize the e.m. energy at zero-velocity in the laboratory frame, in a frequency range where the linear propagation is otherwise forbidden. A recent experiment on slowly-traveling localized states has been reported by Eggleton et al. in an index-modulated fiber through the Kerr effect [2]. However, the trapping of zero velocity solitons within the grating is still an open issue, despite the fact that perfectly steady gap solitons could become the basic elements in all-optical memories. More recently, in the context of parametric quadratic effects, structures with distributed-feedback gratings (DFBG), Bragg-coupled to one or both frequencies in media for Second-Harmonic Generation (SH G), have been shown to support two-color gap solitons, i.e. localized energy states of trapped field components at the fundamental (FF) and its second harmonic (SH), based on the interplay of grating dispersion, parametric gain and cascading phase shifts [3-7]. In this Communication we numerically demonstrate that stationary gap simultons can be excited in a quadratically nonlinear DBFG via inelastic scattering of pulses launched at the FF, and can be detected using a similar ”reading” beam.