EN
A new phenomenological model of self-organized second-harmonic generation is proposed describing the photoinduced χ^{(2)} grating formation as a cumulative third-order nonlinearity via a complex χ^{(2)} encoding function being dependent upon the light intensities of fundamental and second-harmonic writing radiations. The theoretical results attained are confronted with recent experimental measurements by Lambelet and Feinberg and the χ^{(2)} encoding function is constructed for this special case.