Impact of fiber parameters on EDFA and/or Raman amplified high-spectral-efficiency coherent WDM transmissions.

The impact of fiber properties is investigated for coherent systems employing polarization-division multiplexed high-level quadrature amplitude modulation, wavelength-division multiplexing, and erbium-doped fiber amplifier and/or distributed Raman amplification. This is done by comparing the performances of fiber links of various attenuation coefficients and effective areas via experimentally verified analytical methods. Results show that the excess noise, which originates at amplifiers compensating for the losses of filters and switches located between fiber spans, can weaken or even diminish the performance enhancement brought about by lowering the fiber attenuation coefficient, especially if distributed Raman amplification is employed. This leads to the difference in the link performance assessment between our analytical results and some previously published figures of merit (FOM). On the other hand, increasing the fiber effective area results in the same amount of performance improvement regardless of the amplification scheme or the excess noise, which agrees with the FOMs. Since the larger effective area causes poorer pumping efficiency for systems employing distributed Raman amplification, a tradeoff between high performance and low power consumption needs to be determined for such systems.