Study of system performance in a 107-km dispersion-managed recirculating loop due to polarization effects

We investigate the polarization evolution for both signal and noise in two 107-km recirculating loops with polarization-dependent loss per round-trip of 0.35 dB and less than 0.1 dB, respectively. When the system is optimized, in the first case, both signal and noise are polarized, while in the second case, the signal tends to depolarize due to the noise. We experimentally measured and theoretically simulated the Q factor distribution, which is far from what is expected for straight-line systems, after 5000 km in the second case. We also suggest a simple method for obtaining the same Q distribution in recirculating loop experiments as expected in straight-line experiments.