EDFA-Only WDM 4200-km Transmission of OFDM-16QAM and 32QAM

We experimentally demonstrated long-distance transmission of 68.3 Gb/s wavelength-division multiplexing polarization division multiplexing (PDM)-orthogonal frequency division multiplexing (OFDM)-16QAM and 85.5 Gb/s PDM-OFDM-32QAM signals. The PDM-OFDM-16QAM signals have been successfully transmitted over 4242 km with a net spectral efficiency of 5.46 b/s/Hz. Furthermore, utilizing multiband digital back-propagation for nonlinearity compensation, the PDM-OFDM-32QAM signals at 6.84 b/s/Hz net SE have been successfully transmitted over the same distance. After transmission, both 16QAM and 32QAM signals surpassed the 20% soft-decision forward error correction threshold. To the best of our knowledge, these results correspond to the longest transmission distance for the PDM-OFDM-16QAM and PDM-OFDM-32QAM signals with SE higher than 5 and 6.5 b/s/Hz, respectively, by employing only erbium doped fiber amplifier amplification.