Impact and mitigation of XT-induced time-synchronization errors in MDM transmission systems through a minimized residual inter-block-interference (MRI) algorithm

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Multiple-input-multiple-output (MIMO) mode-division-multiplexed (MDM) transmission in few-mode fiber (FMF) has been widely investigated to further enhance the capacity of optical systems and networks. In this paper, for the first time, we discuss the impact and mitigation method of random mode crosstalk induced by perturbations in FMF on timing synchronization in MIMO-MDM transmission. We show by simulation that traditional maximum correlation-based synchronization algorithms are vulnerable to random mode crosstalk and consequently cause performance degradation. To solve this problem, a novel synchronization algorithm based on minimum residual inter-block-interference (MRI) criterion is developed for frequency domain equalization (FDE) MDM systems. Theoretical analysis proves that the MRI algorithm can effectively compensate the crosstalk-induced synchronization error. Then Monte Carlo simulations are carried out under different crosstalk conditions. For 100-km 12 × 12 MDM transmission, Q2-factor improvement up to 8.7-dB has been observed and the system outage probability has been substantially reduced from 0.3 to 5e−4. The proposed MRI timing synchronization will be beneficial for the design of practical MIMO-MDM systems.