  In this article we consider one dimensional model of an ultra short pulse
propagation in isotropic dispersionless media taking into account a
nonlinearity of the third order. We introduce a method for Maxwell's equations
transformation based on a complete set of projecting operators. The operators
generally correspond wave dispersion branches. As a simplest result of the
method application we derive a system of equations describing dynamics of
ultrashort pulses of opposite directions of propagation. We show that in such
way the generalized Short Pulse Equations of Shafer and Wayne is obtained if
the only directed wave is initialized. The effects of the unidirectional pulses
interaction are traced.
