| Summary: | Network traffic between data centers has grown rapidly in recent years. Therefore, an optical modulation format with high spectral efficiency is desired in inter-data center links at data rates of more than 400 Gb/s in each wavelength. In order to further improve the transmission performance in single-span inter-data center links, a nonlinearity-tolerant probabilistically-shaped 4D modulation format with a spectral efficiency of 9 bits/4D symbol is proposed. The proposed modulation format fills the gap between polarization-multiplexed 16- and 32-ary quadrature-amplitude modulation (PM-16QAM and PM-32QAM). In numerical simulations, we compare our proposed modulation format with probability-amplitude-shaped 64QAM (PAS-64QAM) and 512-set-partitioned 32QAM (512SP-32QAM) at a spectral efficiency of 9 bits/4D symbol in a single-span transmission link. The simulation results indicate that the proposed modulation format shows better linear and nonlinear performances than a 512SP-32QAM format. Compared with PAS-64QAM format, the proposed modulation format can provide similar transmission performance with improved fiber nonlinear tolerance.
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