Soliton solutions for an higher ordernonlinear Schroedinger equation in optical fiber

The new improvements to increase the bit rate in optical fiber require thepropagation of pulse whose temporal width is always lesser. This causes thepresence of further terms, linear and nonlinear, in the evolution equationof the pulse. The analysis on the complete integrability of the evolutionequation, in a fiber optics with local properties and achieved in a previouspaper, is improved dealing with the normal dispersion case, which allowsthe dark soliton propagation. In the last section special efforts are made topropose some interesting soliton solutions both bright and dark.