Optical solitons in a dispersion-flattened fiber with linear and quadratic intensity-dependent refractive-index changes

Optical-soliton propagation in a dispersion-flattened fiber is investigated, of which third-order dispersion is nil and fourth-order dispersion exists with linear and quadratic intensity-dependent refractive-index changes. For four possible sign combinations of the second-order dispersion and the Kerr-effect terms, we found that there are two types of bright-soliton solutions and two types of dark-soliton solutions. The magnitude of the fourth-order dispersion parameter is related to the quadratic intensity-dependent nonlinearity coefficient, and their signs are opposite. The peak power and the period of the soliton are determined by the magnitude of the fourth-order dispersion parameter. We numerically show that the bright-soliton solution in anomalous second-order dispersion and the positive Kerr coefficient regime is stable and becomes quasi stable when the Raman effect is considered.