64-Tb/s, 8 b/s/Hz, PDM-36QAM Transmission Over 320 km Using Both Pre- and Post-Transmission Digital Signal Processing

We report the successful transmission of 64 Tb/s capacity (640
$\,\times\,$
107 Gb/s with 12.5 GHz channel spacing) over 320 km reach utilizing 8-THz of spectrum in the
${\rm C}+{\rm L}$
-bands at a net spectral efficiency of 8 bit/s/Hz. Such a result is accomplished by the use of raised-cosine pulse-shaped PDM-36QAM modulation, intradyne detection, both pre- and post-transmission digital equalization, and ultra-large-area fiber. We discuss in detail the digital modulation technology and signal processing algorithms used in the experiment, including a new two-stage, blind frequency-search-based frequency-offset estimation algorithm and a more computationally efficient carrier-phase recovery algorithm.