SINGLE-CHANNEL OPERATION IN VERY LONG NONLINEAR FIBERS WITH OPTICAL AMPLIFIERS AT ZERO DISPERSION

Very long lightwave fiber systems with analog optical amplifiers must operate very close to the zero-dispersion wavelength to avoid pulse distortion. However, in very long fibers, four-wave mixing, self-phase modulation, and cross-phase modulation, due to fiber non-linearity, become important and must be taken into account. We pointed out in an earlier paper [1] that in a system with two wavelength channels, neither channel may be located directly at the zero-dispersion wavelength to avoid catastrophic buildup of four-wave mixing components. In this paper we emphasize that the zero-dispersion wave-length should be avoided even in single-channel operation because of a catastrophic interaction between the signal power and spontaneous emission noise generated in the optical amplifiers.