Reducing interchannel crosstalk in long-haul DWDM systems

Nonlinear interaction between signal channels may result in significant performance degradation in transoceanic dense wavelength-division-multiplexing (WDM) transmission systems operated at high bit rates. In this paper, we report that the nonlinear crosstalk for systems with high spectral efficiency can be suppressed if WDM channels are launched with orthogonal relative states of polarization. It is shown that for adjacent channels (that experience the strongest nonlinear interaction) the launched relative state of polarization is maintained over the large distance of low polarization-mode dispersion fiber typically used in undersea systems. Numerical studies, as well as experimental results, are presented for standard and dispersion slope-matched dispersion maps.