A research team led by Benjamin J. Puttnam at the National Institute of Information and Communications Technology (NICT) reported that it transmitted data over a distance of more than 3000 km (1860 miles) at a rate of 319 Tbit/s and a transmission bandwidth of greater than 120 nm, across the S-, C-, and L-bands. The team used a 4-core optical fiber with a 0.125-mm outer diameter to transmit the data, setting a record for data transmission over an optical fiber with a standard cladding diameter. The signal bandwidth of the long-haul transmission comprised 552 wavelength division multiplexing (WDM) channels. The system uses WDM and a combination of optical amplification technologies to enable long-haul transmission of 552 WDM channels ranging from 1487.8 to 1608.33 nm. The team built a transmission loop that combined erbium- and thulium-doped fiber amplifiers with Raman amplification distributed along the fiber itself to enable the transmission of the wideband signal to recirculate. By combining various amplifier technologies, the researchers built a transmission system that capitalized on the strengths of WDM technology. The Raman amplification portion of the transmission system. Courtesy of the National Institute of Information and Communications Technology. The system measured achievable transmission throughput with each channel with PDM-16QAM modulation at distances of up to 3001 km, where the data rate of 319 Tbit/s was achieved. In addition to the C- and L-bands typically used for high-data-rate, long-haul transmission, the researchers included the S-band in their transmission. Until now, NICT had only built transmission systems that used WDM across the C- and L-bands, along with state-of-the-art modulation technology, to explore high-data-rate transmission in optical fibers. Although S-band transmission has led to several new records for transmission capacity in optical fibers, transmission distance in the S-band has been limited to only a few tens of kilometers until now. The NICT team hopes that its achievement will open the way for systems that can support optical communications at data rates needed for 5G and beyond. The reported transmission demonstrates the potential of spatial division multiplexing (SDM) fibers to support high-throughput SDM fiber systems in the near term, providing they are compatible with existing cabling technologies. The standard-cladding-diameter, 4-core fiber used for the demonstration is compatible with conventional cable infrastructure, and the researchers estimate that its mechanical reliability is comparable to single-mode fibers. A graphic depicting transmission demonstrations using 125-μm-diameter fibers. Courtesy of the National Institute of Information and Communications Technology. NICT said it plans to work to extend its transmission range to transoceanic distances, as well as continue to develop wideband, long-distance data transmission systems to increase the transmission capacity of low-core-count multicore and other new SDM fibers. The research was presented at the International Conference on Optical Fiber Communications (OFC), which took place June 6-11.