  The effect of retaining the material dispersion terms in the nonlinear
coupled mode equations (NLCME) that describe light propagation in fiber Bragg
gratings is analyzed. It is found that dispersion is responsible for new
instabilities of the uniform states and gives rise to new complex spatio
temporal dynamics that is not captured by the standard NLCME formulation. A
detailed analysis of the effect of dispersion on the linear stability
characteristics of the uniform solutions is presented and some numerical
integrations of the NLCME with dispersion are also performed in order to
corroborate the theoretical results.
