In this letter, a novel two-stage digital feed forward carrier recovery algorithm for 64-ary quadrature amplitude modulation (QAM) is proposed and analyzed. Due to the absence of any feedback loop, the approach shows a high tolerance toward laser phase noise. Different steps involving partition, selection, and rotation of symbols are also discussed. For an OSNR penalty of 1 dB at bit error rate of 10-3, the proposed scheme can tolerate linewidth times symbol duration product equal to 3.3×10-5and hence can be used with the commercially available state-of-the-art tunable lasers for 64-QAM transmission at 400 Gb/s.
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Bilal et al. (2014) studied this question.
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