Hardware Efficient and Transceiver IQ Skew-Tolerant DSP Scheme Under Baud-Rate Sampling for Short-Reach Coherent Optical Interconnects

Coherent detection with baud-rate sampling is considered an effective solution for power-sensitive short-reach optical interconnects. To effectively address transceiver IQ skew under baud-rate sampling, this paper proposes a hardware-efficient and transceiver IQ skew-robust baud-rate DSP scheme in self-coherent transmission systems, where it can further reduce cost and eliminate the impact of frequency offset. The proposed scheme independently performs timing recovery on the in-phase (I) and quadrature (Q) components, naturally compensating for transceiver IQ skew. Additionally, a tap-configurable simplified baud-rate equalizer significantly reduces DSP complexity after precise timing synchronization. Through detailed theoretical and simulation analyses, we reveal that the coupling effects resulting from transmitter IQ skew and path mismatch between the signal and local oscillator (LO) light are critical determinants of DSP performance. When using narrow-linewidth ECL lasers, the proposed scheme shows strong tolerance to this coupling effect. Notably, with wide-linewidth DFB lasers, strict control of transmitter IQ skew or path mismatch is necessary to prevent performance degradation. Experimental results from 56 GBaud polarization-multiplexed 16QAM transmission demonstrate that the proposed scheme shows strong stability in BER performance over a wide range of transceiver IQ skew compared to existing baud-rate DSP schemes, reducing the real-valued multipliers for the equalizer by approximately 71%. Compared to traditional DSP schemes (@2 SPS), the proposed scheme has a minimal receiver optical power (ROP) sensitivity penalty while reducing complexity by about 85%.