The propagation in a non-linear dispersive medium is analysed by using differential equation techniques. A dispersive semi-infinite space with a cubic order instantaneous non linearity, is considered. The proposed analysis is based on to transform time dependent Maxwell equations into a slowly varying envelope function differential equation. The derived partial differential equation has many similarities with the so-called Schrödinger equation but it includes an additional term arising from the first order dispersion. This non-linear equation is solved by application of the Inverse Scattering Method for the initial condition |q(x,t = O)| = Asechx. The N-soliton solution is developed analytically in the case of reflectionless potentials. The single and double soliton solution are derived explicitly. Numerical results presenting the pulse propagation inside the non-linear dispersive medium are also given.