Abstract
We investigate the optimal constellation size for probabilistic shaping (PS) under the constraint of different effective numbers of bits (ENOB) of the analog-to-digital converter (ADC) at the receiver. For a fixed entropy, increasing the constellation size brings a larger shaping gain, while it also leads to a higher peak-to-average-power ratio, which makes the signal more sensitive to the ENOB and fiber nonlinearity. Our experimental results show that PS-44 quadrature amplitude modulation (QAM) outperforms both PS-64 QAM and uniformly shaped 32 QAM (U-32 QAM) when the ENOB of ADC is lower than 4.5. The optimal launched power and the maximum achievable distance for U-32 QAM, PS-44 QAM, and PS-64 QAM are analyzed by simulation.
© 2019 Optical Society of America
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