Researchers report the real-time, bidirectional transmission of 78 interleaved, 400-Gb/s channels with a 31.2-Tb/s fiber capacity. The C-band signals were transmitted over a single, 90-km-long single-mode fiber. For their setup, researchers from Nokia used real-time, commercially available transponders and components that are compliant with current network standards. After testing the unidirectional transmission configuration, the team wanted to further improve signal-to-noise power ratio. A bidirectional transmission set up with the same 90-km fiber, where the even and odd 400-Gb/s channels, with the same 50-GHz grid spacing, transmit in opposite directions. Courtesy of Nokia. “It was important for us to maintain simple amplification, only based on erbium-doped fiber amplifiers, and to use standard fibers,” said researcher Thierry Zami. “To increase the system margins observed with the unidirectional setup, we could have decided to make the same unidirectional experiment with slightly larger channel spacing, for instance. But we said no because we wanted to remain compliant as much as possible with the standard grid.” The team instead developed a bidirectional transmission setup with the same 90-km fiber, where the even and odd 400-Gb/s channels, with the same 50-GHz grid spacing, transmit in opposite directions. For this configuration, they measured Q2 margins at least twice as large as for the unidirectional version. Because the setup employs two 100-GHz-spaced multiplexers to create the 50-GHz-channel spacing, unlike the unidirectional system’s individual 50-GHz multiplexer, it benefits from wider filtering to exhibit better tolerance to frequency detuning. Researchers capitalized on a high spectral frequency to boost capacity in the fiber. “The spectral efficiency allows us to provide quite a large fiber capacity. So, in this case we claim 31.2 Tb/s, but in practice, without the limitations in terms of number of loading channels in our lab, we could have reached about 38 Tb/s over whole C-band,” said Zami. Such a high transmission capacity and rate could offer a significant capacity bump to current data center interconnections, where nearby data centers are coupled together to form a single, larger center. The team will demonstrate the technology at the Optical Networking and Communication Conference & Exhibition (OFC 2018), being held March 11-15 in San Diego. Hear 31.2-Tb/s real-time bidirectional transmission of 78- × 400-Gb/s interleaved channels over C-band of one 90-km SMF span (W1B.5), Wednesday, March 14 at 9:15 a.m., San Diego Convention Center, Room 1B.