Optical Gap Solitons in Nonresonant Quadratic Media

We demonstrate an important role of the process of optical rectification in the theory of nonlinear wave propagation in quadratically nonlinear [or ${\ensuremath{\chi}}^{(2)}$] periodic optical media. We derive a novel physical model for gap solitons in ${\ensuremath{\chi}}^{(2)}$ nonlinear Bragg gratings.