On the performance stability of MCF-based SDM system affected by inter-core crosstalk fluctuation

The inter-core crosstalk (IC-XT) of multi-core fiber (MCF) limits the capacity of space division multiplexing system (SDM) fundamentally. We develop a closed-form expression of the magnitude of IC-XT for various types of signals, which can well explain the mechanism of different fluctuation behaviors of the real-time short-term average crosstalk (STAXT) and bit error ratio (BER) for the optical signals with and without strong optical carrier. The experimental verifications with the real-time measurement of the BER and outage probability in a 7 × 10-Gb/s SDM system agree well with the proposed theory and confirm that the unmodulated optical carrier plays a substantial role in fluctuation of BER. The range of fluctuation can be reduced by 3 orders of magnitude for the optical signal without optical carrier. We also investigate the effect of IC-XT in a long-haul transmission system based on a recirculating 7-core fiber loop and develop a frequency-domain IC-XT measurement technique. Longer transmission distance is shown to have a narrower BER fluctuation range, since IC-XT is no longer the only dominant factor on transmission performance.