Characteristics of XPM in coherent optical OFDM WDM transmission systems

We use a self-correlation technique to extract the inter-channel nonlinear effects i.e. cross phase modulation (XPM) induced phase noise and XPM-induced polarization scattering for analyzing the characteristics of XPM in coherent optical orthogonal frequency division multiplexing (CO-OFDM) wavelength-division-multiplexed (WDM) transmission systems under different dispersion compensation (DC) ratios and different walk-off values. Through the analysis, we can clearly see how the DC ratio acts on the XPM by applying this technique. After transmitting 1500 km standard single-mode fiber (SSMF), 12.3 dB phase noise is induced when the DC ratio is changed from 0% to 105%. While the walk-off is varied from 1.6 ps/km to 12.8 ps/km, almost 10.6 dB phase noise is eliminated. Additionally, the phase noise is verified as the dominant distortion in dual-polarization OFDM systems while the XPM-induced polarization crosstalk is proved to be the decisive distortion in dual-polarization QPSK coherent experiment.

► We set up the WDM system for analyzing the characteristics of XPM.
► We can clearly see how the DC ratio acts on the XPM by using this technique.
► 12.3 dB phase noise is induced when the DC ratio is changed from 0% to 105%.
► Increasing walk-off will decrease phase noise significantly.
► Phase noise is proved to be the dominant distortion in CO-OFDM systems.