Gap solitons in a hollow optical fiber in the normal dispersion regime

We investigate the existence and stability of gap solitons in a model of hollow core fiber in the normal dispersion regime. The model is based on a recently proposed model that is modified here to account for the normal dispersion. The linear coupling between the linear dispersionless core mode and nonlinear dispersive surface mode (in the presence of the third order dispersion) gives rise to a bandgap. It is found that the family of gap solitons fills the entire bandgap. The total energy of gap solitons in the normal dispersion are found to be smaller than their counterparts in the anomalous dispersion. Stability of solitons (both quiescent and moving) is studied by means of numerical simulations and linear stability analysis. We have found that gap solitons in this model are subject to an oscillatory instability and therefore are formally unstable. However, in a significant part of the bandgap the instability is very weak. As a result, solitons belonging to that part of the bandgap are virtually stable objects. It is also found that gap solitons in the normal dispersion (both quiescent and moving) are considerably more stable than the solitons in the anomalous dispersion. Collision dynamics of moving solitons and interaction of quiescent solitons are also investigated.