Femtosecond soliton pulses in birefringent optical fibers

Abstract

We consider femtosecond soliton-pulse propagation in a birefringent optical fiber where rapidly oscillating terms, the difference in polarization dispersions, and the difference in group velocities of the two polarization components have to be taken into account. We demonstrate the existence of a novel class of linearly polarized soliton states (with the linear polarization ranging from 0 to 2π). We also find the elliptically polarized soliton states, which do not appear to be acceptable to the coupled nonlinear Schrödinger equations describing the pulse evolution in the birefringent fiber when the different dispersions between the two polarizations are ignored and the group-velocity difference is taken into account. More importantly, the corresponding stability analysis reveals that within certain operating regions the fast soliton can be stable and the slow soliton can be unstable, whereas in the others the fast soliton is unstable and the slow soliton is stable, in contrast to those reported earlier by neglecting different polarization dispersions. On the other hand, both the linearly polarized soliton states and the elliptically polarized soliton states are found to be unstable. This indicates that for high-capacity coherent soliton communication in the femtosecond regime, the pulse must be launched along either the slow or the fast axis of a practical polarization-maintaining fiber. Finally, the potential applications of weakly unstable linearly polarized soliton states for ultrafast soliton switching are discussed.