Analytical and numerical studies of the performance of a nonlinear directional fiber coupler with periodically modulated dispersion

In this paper, we report numerical and analytical studies of the propagation of ultrashort optical soliton pulses in two-core nonlinear fiber couplers constructed with periodically modulated dispersion fiber (PMDF). Our simulations is taking into account different amplitude and frequency modulations. Using the technique developed by Anderson, we convert the coupled nonlinear Schrödinger equations (NLSEs) into a variational problem with a corresponding Lagrangian equations of motion for a finite number of degrees of freedom and obtain the switching characteristics of the device. The transmission characteristics, the critical energy, extinction ratio (Xratio), and the crosstalk level (Xtalk) for first order solitons were studied for low to high pump powers. The analytical and numerical procedure was compared. Comparing both techniques we can say that the analytical procedure (Lagrangian formulation) provide very good description of soliton switching in the PMDF coupler for pump energies below the critical energy of the coupler.