Constant Modulus 4D Optimized Constellation Alternative for DP-8QAM

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Span loss budget vs launch power for 4D-2A8PSK, Quaternary 12b-8D, and DP-8QAM codes for 75 spans of 80km SSMF at a target BER = 10^-2.

We propose a constant modulus 4D format as an alternative to DP-8QAM. It has 0.4dB lower SNR at BER = 10^-2, and 1 dB higher span loss budget in nonlinear regime.