Black solitons in dispersion managed fibre transmission systems

In an ideal continuous exponential varying dispersion fibre, black solitons, like their bright counterpart, can propagate over a long distance without being broadened when the weakened nonlinearity due to the fibre loss is compensated for by the decreasing dispersion. We find, however, that in a practical stepwise decreasing dispersion fibre with N steps, the number of steps N required for well behaved evolution of black solitons in the lossy fibre with negligible distortion/broadening is smaller than that for the bright solitons. This finding indicates that the stepwise varying dispersion in fibers can be more effective for extending the amplifier spacing or reducing required amplifier numbers in the high-bit-rate dark solution transmission system than in the corresponding bright soliton transmission system