Impacts of XPM induced by 16QAM channels on the performance of coherent QPSK receiver with DA-ML carrier phase estimation

We investigate cross-phase modulation (XPM) induced by 16QAM channels in hybrid QPSK/16QAM wavelength division multiplexed (WDM) systems. A power spectral density (PSD) formula is presented to predict the statistical properties of XPM-induced phase noise at the end of dispersion managed (DM) fiber links. We derive the analytical expression of phase error variance for the performance prediction of QPSK channel coherent receiver with decision-aided (DA) maximum-likelihood (ML) phase estimation (PE). Bit error rate (BER) performance in QPSK channel is evaluated and compared through both theoretical derivation and Monte Carlo simulation. The results show that the performance of the QPSK channel will be improved when OOK transmitters are upgraded by 16QAM transmitters. The reported findings will be useful for the upgrades of conventional WDM.