Polarization instabilities of dark and bright coupled solitary waves in birefringent optical fibers

We investigate the stability of the propagation of bright and dark coupled solitary waves that may travel in the orthogonal polarization modes of a birefringent nonlinear optical fiber. In the anomalous dispersion regime, the coupled-solitary-wave decay is self-induced by modulational polarization instability of the dark component background pulse. In the normal dispersion regime, stable propagation only occurs for distances of the order of one linear beat length. We identify different instability mechanisms such as gray soliton formation, polarization wave breaking, polarization dispersion, and self-stimulated Raman scattering that leads to asymmetric coupled-solitary-wave breakup.