Abstract

Optical gap solitons are a promising approach towards the realization of all-optical buffers and memories in nonlinear waveguides with Bragg resonant gratings.[1] The trapping of zero velocity solitons within the grating is still an open issue, although they could become the basic elements in all- optical memories. Recently, structures with Bragg distributed-feedback gratings (DFBG), coupled to one or both frequencies in media for Second-Harmonic Generation (SHG), have been shown to support 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 shift.[2-5] Through numerical integration of coupled evolution equations, we demonstrate that stationary two-color gap solitons can be excited in a quadratically nonlinear DBFG via inelastic scattering of pulses launched at the FF, and "read" using a similar input. For a planar quadratic waveguide close to phase-matching for SHG and with a DFBG coupling z-counterpropagating modes at both the FF and the SH, a perturbative analysis [2-3] shows that stationary bright solitons exist when both FF and SH are close to the lower edge of their respective bandgaps, with envelopes described by the same equations governing quadratic solitons in homogeneous dispersive media. We investigated the evolution of a FF input beam, gaussian in space and in time, into a two-color gap-simulton inside the DFG. This is shown in Fig. 1: after generating SH components at and beyond the linear(uniform)-nonlinear (DFBG) interface, the pulse evolves into a two-color self-confined soliton moving at one third of the group velocity of the FF component. The SH (not shown) follows the FF inside the DFBG.

© 1998 IEEE