Impact of amplitude-modulated channels on amplitude-phase channels with coherent detection in distributed-gain fibre-optic communication lines

A technique for measuring interchannel distortions that occur in fibre-optic communication lines with QAM/CD and IM/DD channels is proposed, and a method for describing distortions in the form of additive noise is presented. On the basis of the proposed technique, measurements are performed in a wide range of conditions and an empirical model is formed to assess the deterioration of the quality of a coherent signal due to the influence of IM/DD channels.