Mode interaction in few-mode optical fibres with Kerr effect.

We generalize the method of projection to orthogonal basis functions of transverse coordinates for a nonlinear (Kerr medium) fibre and apply this method in the case of a two-mode waveguide (each with two polarization modes). We use orthogonal Bessel functions that fit the choice of the cylindrical geometry of a fibre. The coupled nonlinear Schrödinger equations are derived for the envelopes of electromagnetic field wave trains in each mode. Analytic expressions and numerical results for coupling coefficients are given; the nonlinearity parameters' dependence on fibre radius is illustrated by plots and compared with results of other authors. [ABSTRACT FROM AUTHOR]