A new approach using FIT-formulation (Finite Integration Technique) (T. Weiland, Electron. Commun., 31, 116}120 (1977); Int. J. Numer. Model., 9, 295}319 (1996)) for simulating waveguide propagation of optical pulses is presented. FIT-methods are widespread in use for broadband linear simulations. In recent years, several attempts have been made to describe di!erent dispersive material-characteristics such as Drude, Debye or Lorentz dispersion. Today advanced FDTD-formulations (Finite Di!erence Time Domain) also consider non-linear e!ects (P. M. Goorjian and A. Ta#ove, IEEE Opt. ¸ett., 17(3), 180}182 (1992); D. M. Sullivan, IEEE ¹rans. Microwave ¹heory ¹echniques, 43(3), 676}682 (1995)). In the following presented method third-order non-linear e!ects were described, which can be observed in isotropic media in frequency ranges of optical pulses, by updating material polarization terms using classical descriptions of Lorentz dispersion, Raman scattering and the Kerr e!ect. The basic idea is transforming these description formulas into sets of linear di!erential equations and solving them with the help of the general exponential solution.