An international joint research group led by the Photonic Network Laboratory of the National Institute of Information and Communications Technology (NICT) has successfully conducted an experiment involving data transmission over 50 km at a rate of 378.9 terabits per second (Tbps) using a frequency band of 37.6 terahertz (THz), which is the world's largest in optical fiber transmission, and broke the world record for highest transmission capacity achieved using existing optical fiber. A transmission rate of 378.9 Tbps is approximately 11 times the domestic broadband traffic as of last November that can be transmitted over a single fiber. This technology is expected to contribute to the expansion of the capacity of optical communication infrastructure required for meeting the increasing future demand of communication.
Using a new wavelength band in an existing optical network is an economical way to increase communication capacity without installing additional fiber optic cables. The combination of new optical fibers and multiband wavelength division multiplexing technology, which are currently being researched, will also allow for increased capacity of optical networks in the future.
Along with the wavelength bands used in commercial long-distance optical-fiber transmission systems (C and L bands), NICT has developed an optical-fiber transmission system that enables the use of the S and E bands, which are not commercially available, and demonstrated high-capacity transmission. To further increase transmission capacity, it is necessary to expand the wavelength band using the new O and U bands; however, an optical-fiber transmission system that supports all these wavelength bands has not been developed so far.
NICT has designed and developed an optical-fiber transmission system based on multiband wavelength multiplexing technology, which allows the use of the world's largest frequency bandwidth of 7.6 THz and 1505 wavelengths, combining O, E, S, C, L, and U wavelength bands. The transmission system consists of optical fibers, optical amplifiers, transreceivers, optical spectrum shapers, multiplexers, and demultiplexers. The transmission experiment used optical-fiber amplifiers and optical spectrum shapers for each wavelength band, which are manufactured by the international joint research group. The used amplifiers and spectrum shapers include bismuth-doped optical-fiber amplifiers for the O-band, U-band Raman amplifiers, and optical spectrum shapers for the O- and U-bands. By optimally designing the optical signal strength of all wavelength bands considering the wavelength characteristics of the optical fiber, the research group has succeeded in transmitting wavelength multiplexed signals over 50-km distances at a rate of 378.9 Tbps.
Polarization-multiplexed quadrature amplitude modulation (QAM), by which a large amount of information can be handled, was employed for signal modulation, with 16QAM used in the O band; 64QAM used in the E and U bands; and 256QAM in the S, C, and L bands. The transmission capacity and frequency bandwidth achieved in this experiment are 25% and 35% higher than those achieved last October, respectively, which were 301 Tbps and 27.8 THz, respectively, breaking the existing world records for optical-fiber transmission.
The affiliations of the members of this international joint research group (roles in parentheses) are as follows: NICT Photonic Network Laboratory (design and development of the transmission system); Aston University, UK (development of Raman amplifiers); Nokia Bell Labs, US (development of optical spectrum shapers); Amonics, Hong Kong (development of optical-fiber amplifiers and Raman amplifiers); University of Padova, Italy (trainees participated in the transmission experiments); and University of Stuttgart, Germany (participation in the transmission experiments).
The paper reporting the results of this R&D was very highly evaluated at the 47th International Optical Fiber Communication Conference (OFC2024) held in San Diego, USA; accepted as the best hot topic paper (Postdeadline Paper); and presented on March 28, 2024.
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