Dark solitons in optical fibers with higher order effects

We consider the higher order nonlinear Schrodinger (HNLS) equation, which governs the nonlinear wave propagation in optical fibers with higher order effects. Lax pair associated with the integrable HNLS equation for the pulse propagation in normal dispersion regime of the fiber media is constructed with the help of Ablowitz-Kaup-Newell-Segur method. Using Hirota bilinear method, dark soliton solution is explicitly derived. Similar study is also carried out for simultaneous propagation of N nonlinear pulses in the normal dispersion regime of the fiber system with higher order effects.