Accumulation of nonlinear noise in coherent communication lines without dispersion compensation

• Dependence of nonlinear noise power on the number of spans is superlinear.
• Nonlinear noise in a span is constant when accumulated dispersion is >2 ns/nm.
• Nonlinear noises generated in different spans are supposed to be correlated.

The nature of accumulation of nonlinear noise in multi-span communication lines with optical amplifiers without dispersion compensation was investigated experimentally and theoretically. It has been established that the dependence of nonlinear noise power on the number of spans is described by a power function with an exponent greater than 1. It has also been established that the nonlinear noise power generated in one span is practically independent on the amount of dispersion accumulated before this span for the values of accumulated dispersion more than 2 ns/nm. Since the noise power generated in one span does not depend on number of this span, in order to describe the superlinear dependence of total noise on number of spans we can assume that noises generated in different spans are correlated.