2024 Recipients of C&C Prize
Group A
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Dr. Shigeyuki Akiba Formerly President and Chief Executive Officer, |
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Dr. Masatoshi Suzuki Vice-President, Professor, Chitose Institute of Science and Technology |
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Dr. Itsuro Morita Professor,Faculty of Science and Engineering,Waseda University |
Citation
For contributions to the development and implementation of large-capacity, wavelength division multiplexing (WDM) optical submarine cable systems
Achievements
International communications began in the latter half of the 19th century with the laying of a submarine cable providing one telegraph line. This was followed by the appearance of coaxial cables that expanded circuit capacity and that could also be used for making telephone calls. In the 1970s and 1980s, however, satellite communications having even larger circuit capacity became mainstream. Nevertheless, on entering the 1980s, optical fiber and semiconductor lasers came into practical use, and by exploiting the low-loss and broadband properties of optical fiber, large-capacity transmission became possible while decreasing the number of submarine repeaters and decreasing the cost of communications, all of which drove the adoption of optical submarine cables. As for transpacific cables, operation of the 3rd transpacific cable (TPC-3) using optical fiber (capacity per fiber: 280 Mbps) began operation in 1989, TPC-4 (capacity per fiber: 560 Mbps) began operation in 1992, and TPC-5 (capacity per fiber: 5 Gbps), which significantly increased transmission capacity with the introduction of an optical-amplifier-repeater transmission system, began operation in 1995. However, due to a phenomenon whereby the velocity of light waves propagating through optical fiber differs according to wavelength (called wavelength dispersion) and due to the nonlinearity of optical fiber, WDM signal waveforms become distorted, which greatly hindered the implementation of large-capacity optical submarine cable systems spanning a distance of 10,000 km. Against this background, it was KDDI engineers including Dr. Shigeyuki Akiba, Dr. Masatoshi Suzuki, and Dr. Itsuro Morita that were instrumental in increasing the capacity of optical submarine cable systems and upgrading WDM-based optical submarine cable systems in particular, thereby supporting the rapidly expanding demand for Internet communications.
Doctor Akiba began research and development toward the development of a 1.5-μm-band system in which optical fiber loss is minimum, and in 1979, he succeeded in achieving continuous oscillation at room temperature of a 1.5-μm-band semiconductor laser. He then led the development of a distributed feedback laser operating in single mode and contributed to the implementation of TPC-4. He also led the research of high-reliability optical amplifier repeaters, which would become the core technology of TPC-5, and made significant contributions to their practical use. In addition to the above, Dr. Akiba promoted a system that combined large-core optical fiber that suppresses the nonlinearity of optical fiber and low-noise optical amplifiers using 980-nm pumping lasers, and he played a leading role in supervising the development of a WDM optical submarine cable system featuring a speed of 10 Gbps per wavelength.
Doctor Suzuki began research and development of high-speed optical modulators deemed necessary for achieving a high-speed optical submarine cable system. He developed a semiconductor-electro-absorption-type high-speed optical modulator, and in 1987, he succeeded in integrating a semiconductor optical modulator and a distributed feedback laser as a world’s first. In the above ways, he contributed to the realization of large-capacity WDM optical submarine cables using high-speed signals such as the Japan-US cable. Additionally, as a method that compensates for the distortion of signal waveforms due to the nonlinearity of optical fiber and wavelength dispersion, Dr. Suzuki and Dr. Morita invented and demonstrated a new transmission scheme capable of stable, long-haul propagation of 10,000 km or longer for high-speed optical signals. In this scheme using an optical-fiber transmission path that periodically alternates between optical fiber having positive and negative wavelength dispersion, a chirped Gaussian return-to-zero (RZ) optical pulse maintains the same shape over each fixed interval while the waveform periodically changes during the propagation. This scheme also solved the problem of limitations in transmission distance owing to timing jitter (fluctuation in arrival times of optical signals) unique to optical soliton transmission with optical amplifiers, and it was used to demonstrate as a world’s first the possibility of extending the transmission distance of 40-Gbps high-speed optical signals by more than 10 times to longer than 10,000 km. It was also used to realize the world’s first transoceanic transmission in WDM systems with from 16 to 100 of 10-Gbps channels. This technology has been widely adopted as a dispersion-management soliton transmission scheme that is capable of high-quality, stable signal transmission in a dispersion-compensating-fiber transmission system including WDM optical fiber having nonlinearity. As such, it has become a fundamental technology for long-haul optical fiber transmission systems.
The technologies developed by Dr. Akiba, Dr. Suzuki, and Dr. Morita became essential to WDM optical submarine cables and came to be applied to many optical submarine cables from 1999 to 2016 covering a total system length of 206,000 km. These included transpacific (PC-1: 1999, Japan-US: 2001), transatlantic (TAT-14: 2001), and Asia-region (C2C: 2001, EAC: 2002) optical submarine cables as well as 1-Tbps-class transpacific optical submarine cables (TGN-Pacific: 2003, UNITY: 2010). These technologies made a major contribution to the deployment of a global broadband infrastructure supporting communication traffic that increased rapidly due to the spread of the Internet and expanded use of smartphones.
Although capacity has expanded to 10 Tbps in optical submarine cables using digital-coherent technology (FASTER: 2016), a transmission capacity limit (nonlinear Shannon limit) is being approached since the fiber launch power is limited due to the effects of optical fiber nonlinearity. Against this background, Dr. Suzuki and Dr. Morita have been leading research into space division multiplexing (SDM) technology as a future technology that could break through this transmission capacity limit and have been demonstrating the feasibility of a 140-Tbps transoceanic system using new multi-core optical fiber.
Dr. Akiba, Dr. Suzuki, and Dr. Morita pioneered the research and development of technology for expanding the capacity of long-haul optical submarine cables particularly through optical-nonlinearity control. They played a major role in applying this technology to transpacific/transatlantic large-capacity optical submarine cables, which constitute major arteries handling approximately 99% of all international communications. These achievements have had huge ripple effects in academia and industry. They are remarkable on a global basis and have made great social contributions in the C&C (Computers and Communication) field. For these outstanding achievements, it is more than fitting that Dr. Akiba, Dr. Suzuki, and Dr. Morita receive the C&C Prize.