Long-Haul WDM/SDM Transmission Over Coupled 4-Core Fiber With Coupled 4-Core EDFA and Its Mode Dependent Loss Characteristics Estimation

We experimentally demonstrated a long-haul wavelength-division multiplexed (WDM) and space-division multiplexed (SDM) transmission of 32-Gbaud polarization-division multiplexed quadrature phase-shift keying signals over 52-km coupled-4-core fiber spans with amplification by coupled-4-core erbium-doped fiber amplifiers (EDFAs). Error-free performance after forward error correction was achieved up to 2700 km. From converged multi-input multi-output filter coefficients, we estimated the mode dependent loss (MDL) that occurred in this experiment. The MDL was frequency-dependent within a WDM channel and the root-mean square MDL was 1.0 dB per loop. To assess the effect of MDL on SDM transmission performance, we also estimated the outage probability through Monte-Carlo simulations with a Gaussian noise model. The estimated outage probability under MDL showed similar performance to that obtained in the transmission experiment. This suggests that the MDL of coupled-multi-core EDFAs was one of the major limiting factors of the transmission performance and that the rms MDL per span should be below 0.4 dB for further long-haul transmission distance over 6000 km.