Impact of Low-OSNR Operation on the Performance of Advanced Coherent   Optical Transmission Systems
  We find evidence that low-OSNR operation causes substantial penalty on system maximum reach due to non-linearity generated by ASE noise and due to signal-power conversion into non-linear noise. Neglecting these effects may lead to a quite substantial performance prediction error. 
P. Poggiolini, A. Carena, Y. Jiang, G. Bosco, V. Curri, F. Forghieri
physics.optics