Optimized WDM Transmission Impairment Mitigation by Multiple Phase Conjugations

Multiple phase conjugations within a transmission-optimized fiber link enable significant nonlinearity cancellation in the wavelength division multiplexed (WDM) systems. In particular, we demonstrate the fiber impairment mitigation of WDM 24×48 Gb/s dual-polarization quadrature phase shift keying (DP-QPSK) signals using 12 optical phase conjugations (OPC). The power excursion and dispersion-tailored transmission line in which the phase conjugations acted periodically, enabled an 8-dB higher nonlinearity threshold for the WDM 1.1-Tb/s DP-QPSK signals. With the nearly perfect nonlinearity cancellation, large input powers per span became available. Under these circumstances, we also present a first approach to the analysis of the impact of multiple phase conjugations in a distributed Raman amplified link. The analysis considers the performance of the experimentally measured OPC subsystem within an optimized transmission line limited only by an amplified spontaneous emission noise. This raw estimate gives insight into the linear noise performance limit of the employed phase conjugator when inserted multiple times in such a transmission system.