Abstract
We demonstrated the transmission of a Nyquist-WDM signal based on PM-64QAM modulation in an EDFA-only submarine configuration composed of 54.4 km-long fiber spans: 20 channels at 124.8-Gb/s were propagated over 1306 km of low-loss pure-silica-core fiber (PSCF). Thanks to an aggressive digital spectral shaping, we achieved a raw spectral efficiency (SE) of 10.4 b/s/Hz, corresponding to 8.67 b/s/Hz net SE when considering a 20% FEC overhead. Transmitter DACs are operated at a record-low 1.15 samples/symbol, enabled by the insertion of advanced anti-alias filters. The achieved SE-times-distance product was 11,327 (b ∙ km)/(s ∙ Hz), the highest reported so far for PM-64QAM. Combining the experimental results with the performance predictions obtained using an analytical model of nonlinear propagation in uncompensated coherent optical systems (the so-called "GN-model"), we show that PM-64QAM is a realistic option for ultra-high capacity systems in the 1,000 km range, carrying up 40 Tb/s in the C-band.
Highlights
Digital transmission systems at 100 Gb/s operated in WDM configuration based on Polarization-Multiplexed (PM) QPSK with 50 GHz channel spacing are commercially available from several vendors
We demonstrated the transmission of a Nyquist-WDM signal based on PM-64QAM modulation in an EDFA-only submarine configuration composed of 54.4 km-long fiber spans: 20 channels at 124.8Gb/s were propagated over 1306 km of low-loss pure-silica-core fiber (PSCF)
While PM-QPSK outperforms all other formats in terms of SE-times-distance product (SEDP) and it is the clear choice for transoceanic distance over 10,000 km, PM-64QAM together with PM-16QAM can still play an important role in future flexible optical networks
Summary
Digital transmission systems at 100 Gb/s operated in WDM configuration based on Polarization-Multiplexed (PM) QPSK with 50 GHz channel spacing are commercially available from several vendors. Recent improvements in the net spectral efficiency are shown, where the main record breaking experiments of the last five years, based on coherent detection and single–carrier (non-OFDM) QAM modulation, have been considered [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20] Trends in this figure show that any step towards high constellation order, from PM-QPSK up to PM64QAM, generates a significant increase in net SE. In this scenario, where the system throughput may be adapted depending on the reach, PM-64QAM will be able to cover 1,000 km carrying up to 40 Tb/s over the C-band
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