High-Order Harmonic Ambiguity Exclusion for Optical Performance Monitoring Based on Subsampling Technique

As bit rates increase, monitoring signal quality in the optical channel online using bit-error-rate (BER) becomes increasingly challenging.Software synchronization can offer a low-cost solution for monitoring signal quality using eye diagrams and the Q factor.However, existing software synchronization algorithms based on the Chirp-Z Transform (CZT) are susceptible to issues such as harmonic ambiguity and jitter, leading to synchronization failures and the inability to reuse synchronization results.In this paper, we propose a high-order harmonic ambiguity exclusion algorithm through spectrum analysis.The high-order harmonic ambiguity exclusion algorithm was validated through back-to-back (BTB) transmission experiments using 9.6961 GBaud 4-level pulse amplitude modulation (PAM-4) signal in an Intensity Modulation Direct Detection (IM/DD) optical fiber communication system.Compared to the CZT based synchronization algorithm, with an OSNR varying from 22dB to 30dB, our proposed algorithm shows an improvement in synchronization success rate ranging from 4.4% to 29.7%, and a reduction in the standard deviation of the Q factor ranging from 0.044 to 0.307.The results indicate that it improves the synchronization success rate and provides more stable synchronization.