A cost-effective and robust digital signal processing (DSP) scheme is proposed and demonstrated experimentally in a coherent 61 GBaud PDM 16QAM system. In our scheme, multi-stage DSP blocks are used to deal with channel effects, transceiver in-phase and quadrature (IQ) skew, and phase noise. A ${4} \times {4}$ real-valued multiple-input multiple-output (RV-MIMO) with $ N_{1} $ taps is for polarization recovery and receiver IQ skew calibration. After frequency offset compensation, two ${2} \times {2}$ RV-MIMO with $ N_{2} $ taps are used to compensate for chromatic dispersion (CD), inter-symbol interference, transmitter IQ skew, and phase noise. Finally, the residual phase noise is eliminated by the maximum likelihood (ML) estimator. The experimental results indicate that the proposed scheme provides better received optical power sensitivity and CD tolerance than the existing simplified DSP schemes. In addition, the proposed scheme can tolerate transmitter IQ skew up to 7 ps in a 10 km case, which outperforms both simplified and conventional DSP schemes. Meanwhile, the proposed scheme can keep the same transceiver IQ skew and CD tolerance and has reduced complexity by 25% after 10 km links, compared to ${4} \times {4}$ RV-MIMO followed by a transmitter skew compensator. To the best of our knowledge, the proposed scheme is the most cost-effective solution for a high baud rate datacenter interconnects where transmitter IQ skew and CD have to be dealt with.

中文翻译：

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适用于存在发射机 IQ 偏斜和色散的短距离相干系统的经济高效且稳健的 DSP 方案

提出并在相干 61 GBaud PDM 16QAM 系统中实验证明了一种经济高效且稳健的数字信号处理 (DSP) 方案。在我们的方案中，多级 DSP 模块用于处理通道效应、收发器同相和正交 (IQ) 偏斜以及相位噪声。甲$ {4} \倍{4} $实值多输入多输出（RV-MIMO）与$ N_ {1} $抽头为偏振回收和接收机IQ偏移校准。经频偏补偿后，两个${2}\times {2}$ RV-MIMO with $N_{2} $抽头用于补偿色散 (CD)、符号间干扰、发射机 IQ 偏差和相位噪声。最后，通过最大似然 (ML) 估计器消除残余相位噪声。实验结果表明，与现有的简化 DSP 方案相比，所提出的方案提供了更好的接收光功率灵敏度和 CD 容限。此外，所提出的方案在 10 公里的情况下可以容忍高达 7 ps 的发射机 IQ 偏斜，这优于简化和传统的 DSP 方案。同时，与${4} \times {4}$相比，所提出的方案可以保持相同的收发器 IQ 偏斜和 CD 容限，并且在 10 km 链路后将复杂度降低了 25%RV-MIMO 后接发射机偏移补偿器。据我们所知，对于必须处理发射机 IQ 偏斜和 CD 的高波特率数据中心互连，所提议的方案是最具成本效益的解决方案。