Robust OSNR system margin and OSNR system penalty monitoring techniques using an optical coherent receiver

We discuss the performance of OSNR system margin and OSNR system penalty monitoring techniques based on the use of an optical coherent receiver. For a 120 Gb/s DP-QPSK transmission system, we demonstrate that we can use the overall link impairment level parameter as a measure of the OSNR system penalty regardless the type of the link impairment as long as the assumption of impairment induced noise gaussianity is valid.