Quasi-particle approach for interacting optical multiple pulses

Employing a high-dimensional variation-of-action method (VAM) with an optimized Lagrangian, we derive an efficient model for the propagation and nonlinear interaction of many pulses in optical transmission. In analogy to particles, each pulse is characterized as a quasi-particle (quasi-particle approach, QPA) with a finite set of essential parameters. In the finite-dimensional system of ordinary differential equations for the evolution of these parameters, the contributions of single particle propagation and collisions are captured. The theory is applied to practical transmission systems using return-to-zero (RTZ) coding as well as differential phase-shift keying (DPSK). All results are confirmed by full numerical simulations of the cubic nonlinear Schrödinger equation.