Microsoft ends support for Internet Explorer on June 16, 2022.
We recommend using one of the browsers listed below.
- Microsoft Edge（Latest version）
- Mozilla Firefox（Latest version）
- Google Chrome（Latest version）
- Apple Safari（Latest version）
Please contact your browser provider for download and installation instructions.
December 9, 2024
NTT Corporation
World's first space division multiplexing long-distance optical transmission experiment of up to 455 terabits per second in the terrestrial field environment
Demonstration of long-distance transmission up to 1000 km by coupled-core multicore fiber cable
News Highlights:
- In a field environment where the signal propagation environment in optical fiber cables fluctuates due to external disturbances such as wind and rain, we succeeded for the first time in the world stable transmission experiment with the record field capacity of 455 terabits per second (more than 50 times that of the current system).
- By mounting and connecting 12-coupled-core multicore fibers with the same diameter as existing optical fibers suitable for mass production to commercial high-density multicore cables, and by developing large-scale MIMO signal processing technology, high-capacity long-distance transmission over 1000km (equivalent to the distance between Tokyo and Osaka) was realized even in the presence of external disturbances.
- This achievement was presented as a post-deadline paper at ECOC2024, the world's largest international conference on optical communications.
TOKYO - December 9, 2024 - NTT Corporation (Headquarters: Chiyoda Ward, Tokyo; Representative Member of the Board and President: Akira Shimada; hereinafter "NTT") has succeeded for the first time in the world in demonstrating stable signal transmission at a maximum rate of 455 terabits per second under field conditions in which the signal propagation environment inside optical fiber cables varies due to external disturbances.
In the demonstration experiment, we demonstrated a high-capacity transmission of 455 terabits per second over a transmission distance of 53.5km by applying large-scale MIMO1 signal processing technology in a terrestrial field environment in which a 12-core fiber with the same diameter as existing optical fibers suitable for mass production was mounted and connected to a commercial high-density multicore cable. Furthermore, we succeeded in amplified transmission at a high capacity of 389 terabits per second over a transmission distance of 1,017 km, which can cover the distance between Tokyo and Osaka, the main artery of Japan's optical backbone network (Figure 1). This result is expected to be a fundamental technology for realizing future terrestrial optical transmission systems with transmission capacity more than 50 times that of conventional systems.
This achievement was adopted and presented as a post-deadline paper [1] at the most challenging presentation session at the world's largest international conference on optical communication technology (50th European Conference on Optical Communication (ECOC)), held in Frankfurt in September 2024. This achievement partly includes the results obtained through research commissioned by the National Institute of Information and Communications Technology (NICT) in collaboration with Sumitomo Electric Industries, Ltd. (hereinafter, "Sumitomo Electric") and Chiba Institute of Technology.
Figure 1 The world's first high-capacity, long-distance optical transmission experiment using 12-coupled-core fiber cables in terrestrial field environment
Background
The amount of data traveling around the world continues to grow exponentially with the proliferation of high-capacity mobile networks and the increase in communications between data centers to support ever-developing AI technologies. This trend is expected to continue in the future, and terrestrial backbone optical networks will need to respond to continued capacity increase to support demand.
For more than 40 years since the commercial introduction of optical communications, current networks have used optical fibers that have a structure with a single waveguide, called a core, through which light passes in a single fiber. In contrast, research and development of space division multiplexing optical transmission using multicore fibers, which increases the number of spatial channels by increasing the number of cores per fiber and transmitting optical signals in parallel, is progressing and is expected to be a fundamental technology for future high-capacity backbone optical networks that can expand transmission capacity. To expand the number of spatial channels to 10 or more while maintaining the same diameter (0.125 mm) as existing optical fibers in terms of compatibility with existing systems and mass productivity, a coupled-core multicore fiber2, which intentionally allows crosstalk of optical signals between adjacent cores is promising. Coupled-core multicore fibers enable high-capacity optical transmission because coupling between the signals can be undone by combining digital signal processing at the receiver after receiving the signal. Compared with a conventional multimode fiber, which can also achieve a high spatial channel count, it has a higher degree of freedom in designing the propagation state of optical signals, and it can reduce propagation delay dispersion3. This makes it possible to reduce the computational complexity of digital signal processing to follow fluctuations in the actual environment due to external disturbances such as wind and rain and is expected to realize optical transmission with reduced power consumption and cost.
In research on coupled-core multicore fibers to date, the feasibility of transoceanic long-distance transmission4 has been verified using fiber spools placed in a laboratory environment. On the other hand, to deploy this fiber terrestrial transmission systems, it is important to verify stable high-capacity transmission in a field environment where the signal propagation environment inside the optical fiber cable changes dynamically.
In this project, we constructed a cable of 12-coupled-core fiber, in which signal coupling occurs between 12 cores, while significantly reducing propagation delay dispersion, and installed it in a tunnel or aerial section emulating a terrestrial field environment. We succeeded in the world's first 12-core fiber field inline-amplified transmission experiment by combining it with precise large-scale MIMO signal processing technology that can tolerate maintenance work in the installation environment and disturbances such as wind and rain, and demonstrated the feasibility of stable high-capacity transmission for the first time in the world (Figure 2).
Figure 2 Trend of Large Capacity Space Division Multiplexing Transmission Experiment in Field Environment Using Fiber with The Same Standard Outer Diameter As Existing Optical Fiber
Key points of the technology
- Multicore fiber field validation environment
In this research, we installed 4.86 km of 12-coupled-core fiber cables on NTT Yokosuka R&D Center and set up a field verification environment for large-scale transmission experiments (Figure 3, Left). Most of the cables are laid in underground tunnels, and 0.2 km of the cables are laid overhead between utility poles on the ground, simulating an actual field installation environment. For the installation, 12-coupled-core fibers were included as part of a 200-core cable with the same configuration as in the commercial system. In this implementation, the fiber [2] and cable [3] were designed in consideration of the coupling state between cores to achieve both the world's smallest-class propagation delay dispersion and low transmission loss, including bending characteristics after cabling, and to enable high-capacity wavelength division multiplexing6 transmission using a wide optical bandwidth including the entire wavelength band (C-band)5 suitable for long-distance optical transmission. - Low loss connection technology between coupled-core multicore fibers
Commercial terrestrial networks contain many splices or connectors between repeaters. This time, Sumitomo Electric's newly developed fiber fusion splicing technology for high-precision couple-core multicore fusion function and Chiba Institute of Technology's connector technology [4] for stable low-loss connection (Figure 3, Right) were applied to direct connection between multicore fibers in the field verification environment. The optical loss of both types is as low as that of conventional single-mode fiber-to-fiber connections. In addition, the loss variation7 between spatial channels is small, contributing to stable transmission. In this experiment, 11 fibers in a cable were connected in a loop to build a field environment recirculating loop transmission evaluation system8 with a span length of 53.5 km.
Figure 3 Multicore Cable Section Overview (left) and Multicore Connector (right)
- Ultra-large capacity MIMO transmission and reception technology
For digital signal processing at the receiver, we applied MIMO signal processing technology that compensates for the dynamically changing optical coupling state and the deviation from the ideal performance inside the optical transceiver with ultra-high accuracy, and demodulate the transmission signal from the distorted received signal after transmission over a maximum distance of 1,000 km. We adopted a polarization-multiplexed PCS-36QAM9 signal with a symbol rate of 140 gigabaud10 as a signal format that can use frequencies efficiently at high speeds. By combining integrated circuit technology and digital signal processing technology developed by NTT, we have realized a high-capacity channel configuration of up to 15.0 terabits per second per wavelength channel. In this transmission experiment, we achieved high capacity by combining 12-core multiplexing and 31 wavelength division multiplexing over the 4.65 THz band over the entire C-band.
Overview of high-capacity field transmission
In this experiment, we first evaluated propagation delay dispersion and optical loss variation, which are parameters that characterize signal quality in the field verification environment, over a period of one hour and confirmed that they showed stable values (Figure 4). This result supports the feasibility of stable spatial and wavelength division multiplexing transmission in field environments.
Figure 4 Evaluation Results of Time Dependence of Transmission Parameters of Field-Installed 12-Coupled-Core Fiber Transmission Line
Next, we evaluated the signal quality of each wavelength channel signal after transmission (Figure 5). As a result, we confirmed that each wavelength signal has a transmission capacity of more than 14 terabits per second over a transmission distance of 53.5 km, with a total transmission capacity of 455 terabits per second. This is the largest-capacity space division multiplexing transmission experiment ever conducted in a terrestrial field environment, and corresponds to more than 50 times the transmission capacity of the current terrestrial system11. Even over a transmission distance of 1017 km, we achieved a total transmission capacity of 389 terabits per second with each wavelength signal having a capacity of 12 terabits per second or more. This distance is sufficient to cover the distance between Tokyo and Osaka which is the main artery of Japan's core optical network, and is expected to contribute to the realization of large-capacity long-distance optically amplified transmission systems in terrestrial field environments using coupled-core multicore fibers with more than 10-cores in the future.
Figure 5 High-Capacity Field Transmission Results
Outlook
In the future, by further advancing research and development of this technology in collaboration with related technology fields, we aim to realize high-capacity terrestrial networks, which will contribute to the realization of infrastructure for the IOWN12 concept and the Beyond 5G/6G era in the 2030s.
Support for this research
Part of this achievement was obtained through commissioned research by the National Institute of Information and Communications Technology (NICT) (JPJ012368C01001).
[Reference]
1A. Kawai, K. Shibahara, M. Hoshi, M. Nakamura, T. Kobayashi, R. Imada, T. Mori, T. Sakamoto, Y. Yamada, K. Nakajima, M. Nagatani, H. Wakita, Y. Shiratori, H. Yamazaki, H. Takahashi, S. Endo, T. Hasegawa, R. Nagase, and Y. Miyamoto, "389.3-Tb/s 1017-km C-band Transmission over Field-Installed 12-Coupled-Core Fiber Cable with >12-Tb/s Spatial MIMO Channels," in Proceedings of 50th European Conference on Optical Communications, Frankfurt, Germany, 2024, Th3B.1.
2R. Imada, T. Sakamoto, T. Mori, Y. Yamada, and K. Nakajima, "Bending Loss and Cut-Off Wavelength Properties of Randomly Coupled Multi-Core Fiber," Journal of Lightwave Technology (Early Access).
3T. Mori, R. Imada, T. Sakamoto, Y. Yamada and K. Nakajima, "Randomly-coupled multi-core fibre cable with flattened spatial mode dispersion over S-L band," in Proceedings of 49th European Conference on Optical Communications, Glasgow, UK, 2023, pp. 163-166.
4Y. Fujimaki, S. Takura, D. Nozaki, and R. Nagase, "Connection characteristics of coupled multi-core fiber connectors," in Proceedings of 2023 IWCS Cable & Connectivity Industry Forum, Orlando, United states, pp. 7-2, 2023.
[Glossary]
1MIMO
Stands for multi-input multi-output. Originally a technical term used in the wireless field, it refers to a technology for parallel communication of multiple different data between transceivers at the same frequency. In the optical transmission field, MIMO technology can be expected to improve transmission capacity by utilizing polarization and spatial modes in optical fibers.
2Coupled-core multicore fiber
An optical fiber that is designed to have propagation characteristics suitable for long-distance transmission by providing multiple optical transmission paths (cores) within the optical fiber and appropriately designing interference between optical signals leaking from each core.
3Propagation delay dispersion
A measure of the variation in arrival time at the receiver between optical signals passing through each core. If this value is large, the load on the receiving side of signal processing increases, which leads to an increase in power consumption of the signal processing circuit.
4NEC and NTT successfully conduct first-of-its-kind long-distance transmission experiment over 7,000km using 12-core optical fiber ~Progress toward increasing capacity of transoceanic optical submarine cables~
https://group.ntt/en/newsrelease/2024/03/21/240321a.html
https://www.nec.com/en/press/202403/global_20240321_04.html
5C-band
C-band (defined in the wavelength range of 1530 -1565 nm) is a typical optical communication wavelength band used for long-distance optical communication as a low-loss wavelength of silica optical fiber, and has been internationally standardized by the International Telecommunication Union (ITU-T).
6Wavelength division multiplexing
This method increases the total transmission capacity by transmitting signals of various wavelengths (colors of light) in parallel within a single fiber.
7Loss variation
This index indicates the loss difference between the optical signals passing through each mode. If this value is large, the total transmission capacity will be reduced, and the stability of signal transmission will be impaired.
8Recirculating loop transmission evaluation system
By connecting optical amplifiers and transmission line fibers in a loop and controlling the input/output timing of optical signals with an optical switch, this experimental method enables testing of optically amplified transmission over long distances with a small number of equipment.
9PCS-36QAM
PCS (Probabilistic Constellation Shaping) is a technology that reduces the signal-to-noise ratio requirement for signal transmission by optimizing the signal distribution based on information theory. QAM (Quadrature Amplitude Modulation) is a modulation method that adds information to both the amplitude and phase of the signal light. 36QAM has 36 signal points. By applying PCS technology to the QAM system, the signal quality can be optimized according to the transmission line conditions.
10Gigabaud (symbol rate unit)
The number of times a light waveform is switched per second. The 140 gigabaud optical signal transmits information by switching the optical waveform 140 billion times per 1 second.
11Current terrestrial system
Wavelength multiplexing of 80 wavelength channels at a transmission rate of 100 Gbps per wavelength channel enables transmission of 8 Tbps capacity per fiber.
https://journal.ntt.co.jp/backnumber2/1410/files/jn201410054.pdf (Japanese link only)
12IOWN
https://group.ntt/en/newsrelease/2019/10/31/191031a.html
About NTT
NTT contributes to a sustainable society through the power of innovation. We are a leading global technology company providing services to consumers and businesses as a mobile operator, infrastructure, networks, applications, and consulting provider. Our offerings include digital business consulting, managed application services, workplace and cloud solutions, data center and edge computing, all supported by our deep global industry expertise. We are over $97B in revenue and 330,000 employees, with $3.6B in annual R&D investments. Our operations span across 80+ countries and regions, allowing us to serve clients in over 190 of them. We serve over 75% of Fortune Global 100 companies, thousands of other enterprise and government clients and millions of consumers.
Media contact
NTT Science and Core Technology Laboratory Group
Public Relations
nttrd-pr@ml.ntt.com
Information is current as of the date of issue of the individual press release.
Please be advised that information may be outdated after that point.
NTT STORY
WEB media that thinks about the future with NTT
