Effects of Modulational Instability on Coherent Transmission Systems.

The modulational instability of the lightwave in fibers with anomalous dispersion produces growth of initial side bands generated by the modulation and deteriorates the transmission capability of a coherent transmission system. Since the growth rate is proportional to the carrier intensity, the repeated amplification of the carrier degrades the signal to noise ratio in proportion to the product of the number of amplifications and the initial carrier intensity. In a nominal parameter of a few mW power system, the e-folding distance of the noise to signal ratio is on the order of a few hundred km.