OSNR monitoring in presence of fiber nonlinearities for coherent Nyquist-WDM system

•A new OSNR monitoring method is proposed in presence of fiber nonlinearities.•The proposed method based on the correlation function is verified in Nyquist -WDM system.•The method achieves monitoring error less than 1.5 dB in the OSNR range of 10–24 dB.•The method is insensitive to the distances, channel input powers and number of WDM channels.

A new method of optical signal-to-noise ratio (OSNR) monitoring in presence of fiber nonlinearities, suitable for Nyquist Wavelength Division Multiplexing (Nyquist-WDM) coherent optical transmission system, is proposed, in which the correlation function (CF) between the symbols who come from neighboring channels is used. The effectiveness of the proposed method is numerically verified in a 28 Gbaud per channel Nyquist-QPSK-WDM coherent system. The results show that, under the configuration with fiber nonlinearities, this method can achieve OSNR monitoring with the error less than 1.5 dB in the OSNR range of 10–24 dB, and keep valid regardless of the transmission distances, channel input powers and number of WDM channels.