Pulse switching in nonlinear fiber directional couplers

A comprehensive analysis of the propagation of short pulses in fiber nonlinear directional couplers is presented. In particular, the limitations as well as the merits of the variational approach to describe power- and phase-controlled pulse switching are discussed. Relying on beam propagation calculations a trial function that accounts for variable width, amplitude, phase, and chirp of the pulses is proposed. The corresponding Euler-Lagrangian equations for the pulse parameters are derived and solved. Concerning power-controlled switching an excellent agreement of the switching curve with beam propagation results is found. Moreover, even the evolution of the various pulse parameters is shown to be described reasonably by the analytical model used. Eventually, optimum criteria for efficient phase-controlled switching may be easily derived by using the model presented.