Fiber nonlinearity-insensitive OSNR monitoring for coherent PM-QPSK-Nyquist-WDM system

We propose a promising fiber nonlinearity-tolerant optical signal-to-noise ratio (OSNR) monitoring technique for high speed long haul polarization multiplexed-quadrature phase shift keying (PM-QPSK) Nyquist wavelength division multiplexing (WDM) coherent optical fiber transmission system, in which the correlation function between the symbols in all states of polarization as well as neighboring channels are exploited instead of the traditional GN model, thus it does not need the prior knowledge of the fiber transmission link nor the complicated integrals. The method is demonstrated to have the OSNR measurement error below 1.28 dB over a wide OSNR range from 10 dB to 28 dB in 100 Gb/s per channel PM-QPSK-Nyquist-WDM system when the launch power is up to 4 dBm and transmission distance is as long as 1600 km.