Propagation of short pulses in birefringent single-mode fibers is considered. Initial pulses are assumed to be linearly polarized at an arbitrary angle with respect to the polarization axes. The Kerr nonlinearity leads to a substantial interaction between the partial pulses in each of the two polarizations. When the amplitudes of the partial pulses are equal, it is found that above a certain amplitude threshold, whose size increases with birefringence, the two partial pulses lock together and travel as one unit. This unit can be a single soliton or, at higher amplitudes, a breather. At the same time, the central frequencies of both polarizations shift just far enough so that, if a rapid oscillation is ignored, their group velocities become identical. When the initial amplitudes are unequal, it is found as before that above a certain threshold one or more solitons emerge from the initial pulse. However, the breathers that appeared when the amplitudes were equal are unstable; they break up into two distinct solitons moving at different velocities when the amplitudes become slightly unequal. It is further shown that realistic fiber attenuation has little effect on these results. The numerical method used to obtain these results is described in detail.
© 1988 Optical Society of America
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