Analysis of modulated linear wave packets and gap solitons in coupled optical fibers

A coupled pair of waveguides with refractive indices of different signs is considered. It is shown that the gap in the linear wave spectrum closes if these waves are amplitude modulated. To look for solitons as envelopes of exponentially modulated wave packets, the dispersion law of these packets is used. Different decompositions of the dispersion law lead to solutions related to different parts of the spectrum. Numerical calculations demonstrate a good agreement with analytical predictions.