Inter-channel skew measurement in multi-core fibers via nonlinear curve fitting of cross-correlation peaks

Inter-channel skew (ICS) measurement is essential for synchronization, optical performance monitoring (OPM), and scalability in space-division multiplexing (SDM) systems based on multi-core fibers (MCFs). We propose a high-accuracy and low-complexity ICS measurement method based on digital nonlinear curve fitting of cross-correlation (Xcorr) peaks. Without increasing the sampling rate and with only negligible additional computational overhead, the method achieves skew estimation accuracy equivalent to upsampling by a factor exceeding 100, while operating at a native sampling rate of 20 GSa/s. The proposed method achieves root-mean-square errors (RMSEs) of 207.97 fs and 177.68 fs on 12-km and 41-km 7-core fibers, respectively, as validated experimentally. Overall, our proposed method achieves high measurement accuracy with low computational complexity, paving a feasible path toward real-time online ICS monitoring in optical transmission links.