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Linear and Nonlinear Compensation for 8-QAM SC-400G Long-Haul Transmission Systems

Digital signal processing (DSP) with both linear equalization and nonlinear compensation for the single-carrier 400G system based on 84-GBaud polarization-division multiplexing 8QAM signals is studied in this paper. The 8QAM signals are generated and preprocessed with pre-equalization and lookup table predistortion at the transmitter (Tx)-side. The implementation principles of training-based adaptive equalization and predistortion are presented in this paper with experimental studies on the tap and memory length. At the receiver (Rx)-side, fiber-nonlinearity compensation based on digital backward propagation is also utilized to further improve the transmission performance. Thanks to the Tx-side and Rx-side DSPs, eight channels of 400G are successfully transmitted over 2125 km SSMF with EDFA-only amplification.