7 x 224-Gb/s WDM Transmission of Reduced-Guard-Interval CO-OFDM with 16-QAM Subcarrier Modulation on a 50-GHz Grid over 2000 km of ULAF and Five ROADM Passes

We demonstrate wavelength-division-multiplexed transmission of seven 224-Gb/s reducedguard-interval CO-OFDM channels with 16-QAM subcarrier modulation on a 50-GHz grid, resulting in a net spectral efficiency of 4 b/s/Hz. Transmission over twenty 100-km ultra-large-area fiber spans and five wavelength-selective-switch passes is achieved. Introduction Aiming to sustain the capacity growth in optical networks, high spectral-efficiency (SE) transmission with per-channel data rates beyond 100 Gb/s is being actively researched. Perchannel data rates of about 1 Tb/s have been demonstrated at an intrachannel SE ranging from 3.1 to 3.7 b/s/Hz by using multi-band coherent optical orthogonal frequency-division 1,2 multiplexing (CO-OFDM) and multi-carrier nowith guard-interval (NGI) CO-OFDM3 polarization-division-multiplexed (PDM) quadrature phase-shift keying (QPSK). Recently, a 448-Gb/s signal based on reducedguard-interval (RGI) CO-OFDM with 16-QAM subcarrier (SC) modulation was generated4 with an intrachannel SE of ~7 b/s/Hz. To assess achievable system SE, wavelength-divisionmultiplexed (WDM) transmission is needed. Using 16-QAM, WDM transmission at net system SEs of 6.4 and 4 b/s/Hz were demonstrated at 171 Gb/s/channel with 240-km reach5 and 224 Gb/s/channel with 1200-km reach6, respectively. Using 36-QAM, WDM transmission at 8-b/s/Hz SE was demonstrated at 107 Gb/s/channel with 320-km reach7. For optical backbone transport systems, it is desired to achieve high SE at high channel data rate while also achieving long-haul transmission.