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Flexible grid spacing using Nyquist-shaped channels for undersea transmission

In this paper, we experimentally study DC-PM-BPSK, PM-QPSK, and PM-16QAM at 35 Gbaud for undersea transmission in a WDM environment with frequency spacing ranging from 50 GHz (DWDM) to 33 GHz (Super-Nyquist). The experimental study focuses on noise, linear cross-talk, and nonlinear tolerance in two undersea applications: (1) Legacy dispersion-managed submarine cables up to 5,000 km in length and (2) New uncompensated submarine cables up to 12,500 km in length. We experimentally demonstrate that a reduction in frequency spacing below the symbol rate can be achieved, and quantify the performance penalties. We also show a comparison of performance and reach between legacy dispersion-managed applications, and new uncompensated applications, as the frequency spacing is reduced below the symbol rate. It is shown that the constellation and line system dispersion map have a significant impact on the tolerance to linear and nonlinear interference generated by narrow frequency spacing.