Coherent point-to-multi-point (PtMP) optical network based on digital subcarrier multiplexing (DSCM) has been a promising technology for metro and access networks to achieve cost savings, low latency, and high flexibility. In-phase and quadrature (IQ) impairments of the coherent transceiver (e.g. IQ skew and power imbalance) cause severe performance degradation. In the DSCM-based coherent PtMP optical networks, it is hard to realize far-end IQ-impairments estimation for the hub transmitter because the leaf on one subcarrier cannot acquire the signal on the symmetrical subcarrier. In this paper, we propose a far-end IQ-impairments estimation based on the specially designed time-and-frequency interleaving tones (TFITs), which can simultaneously estimate IQ skews and power imbalances of the hub transmitter and leaf receiver at an individual leaf. The feasibility of the TFITs-based IQ-impairments estimation has been experimentally verified by setting up $8$Gbaud/SC$\times$$4$SCs DSCM-based coherent PtMP optical network. The experimental results depict that the absolute errors in the estimated IQ skew and power imbalance are within $\pm 0.5$ps and $\pm 0.2$dB, respectively. In conclusion, TFITs-based IQ-impairments estimation has great potential for DSCM-based coherent PtMP optical networks.

翻译：基于数字子载波复用（DSCM）的相干点对多点（PtMP）光网络已成为城域网与接入网中实现低成本、低延迟和高灵活性的有前景技术。相干收发机中的同相正交（IQ）损伤（如IQ偏斜和功率不平衡）会导致严重的性能下降。在基于DSCM的相干PtMP光网络中，由于单子载波上的叶节点无法获取对称子载波上的信号，因此难以实现针对集线器发射机的远端IQ损伤估计。本文提出了一种基于时频交错导频（TFITs）的远端IQ损伤估计方法，该方法可在单个叶节点处同时估计集线器发射机和叶节点接收机的IQ偏斜与功率不平衡。通过搭建$8$Gbaud/SC$\times$$4$SCs的DSCM相干PtMP光网络实验，验证了基于TFITs的IQ损伤估计的可行性。实验结果表明，IQ偏斜和功率不平衡的估计绝对误差分别控制在$\pm 0.5$ps和$\pm 0.2$dB以内。综上，基于TFITs的IQ损伤估计在基于DSCM的相干PtMP光网络中具有巨大潜力。