We consider the Hirota equation which governs the propagation of nonlinear waves in optical fibres with higher-order effects like third-order dispersion, self-steepening and delayed nonlinear response. By using the Hirota bilinear method a special two-soliton solution is derived. We also undertake a special limit corresponding to the multiple-pole case. Physically, this special pair of solitons separates very slowly.
- NONLINEAR SCHRODINGER-EQUATION