Japan’s journey to becoming a leader in fiber optic network expansion is a story of vision, perseverance, and strategic investment. From its early adoption of Fiber-to-the-Home (FTTH) technology to breaking world records in broadband speed, Japan has consistently been at the forefront of digital connectivity.
At the turn of the 21st century, Japan recognized the need for a faster, more reliable internet infrastructure to support its rapidly growing digital economy. Traditional copper-based networks were no longer sufficient to meet the increasing demand for high-speed internet, prompting the government and private sector to collaborate on a nationwide fiber optic rollout.
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A New Digital Era: 5G and Fiber Integration
The launch of 5G networks in March 2020 marked another milestone in Japan’s telecommunications sector. Major operators like NTT DOCOMO, KDDI, and SoftBank began rolling out commercial 5G services, relying heavily on fiber optics to enable ultra-fast and low-latency connections. The deployment of millimeter-wave (mmWave) 5G required extensive fiber backbone networks, reinforcing the importance of continued investment in fiber optics.
Notably, NTT DOCOMO heavily relied on fiber optics to enable ultra-fast and low-latency connections. Since launching its commercial 5G services in March 2020, the company has continuously explored new ways to enhance wireless connectivity, particularly in indoor environments where high-frequency (HF) radio waves struggle to penetrate.
To address this issue, NTT DOCOMO conducted groundbreaking research into radio-penetrable windows, exploring two innovative approaches. Firstly, the company partnered with YKK AP America Inc., an American window manufacturer, to test a new type of window prototype infused with aerogel (a lightweight, highly-porous material historically used in NASA spacesuits). With a dielectric constant close to air, aerogel allows radio waves to pass through more easily, improving indoor signal reception.
NTT DOCOMO is actively experimenting with different materials, shapes, and window structures to optimize radio wave penetration for 5G and future 6G networks. By refining these designs, the company aims to create windows that allow seamless connectivity without compromising structural integrity or energy efficiency.
At its Yokosuka research and development (R&D) center, NTT DOCOMO trialed a cutting-edge transmissive metasurface layer, which can be applied to windows to bend radio waves and direct them toward indoor areas where people need connectivity. This technology uses subwavelength-spaced optical scatterers to adjust the path of passing waves, enhancing coverage without requiring additional base stations.
NTT DOCOMO believes that metasurface technology could play a key role in constructing massive multiple-input multiple-output (MIMO) systems, reducing the number of antennas needed for large-scale configurations. This could significantly lower the cost of 5G and 6G infrastructure, making high-speed wireless connectivity more efficient and accessible.
Moreover, as demand for ultra-fast, low-latency connectivity grows, KDDI has turned to cutting-edge fiber optic advancements to enhance its 5G network. In collaboration with Fujitsu Limited, KDDI Research has successfully developed a large-capacity multiband wavelength multiplexing transmission technology that significantly increases the efficiency of existing optical fiber networks.
Traditional commercial optical fiber networks primarily operate within the C-band (1,530 nm to 1,565 nm), but as data traffic surges, this range is becoming insufficient. KDDI’s breakthrough technology expands usable wavelength bands to include the L-band (1,565 nm to 1,625 nm), S-band (1,460 nm to 1,530 nm), U-band (1,625 nm to 1,675 nm), and O-band (1,260 nm to 1,360 nm). This expansion increases wavelength transmission capacity by 5.2 times compared to conventional C-band-only transmission.
By utilizing batch wavelength conversion and multiband amplification, KDDI is able to transmit data more efficiently over medium- and long-distance optical fiber networks. This facilitates cost-effective capacity expansion in urban and densely populated areas where installing new fiber is difficult.
One of KDDI's most significant achievements is the successful application of coherent dense wavelength division multiplexing (DWDM) transmission technology in the O-band. Traditionally, transmission in the O-band was challenging due to non-linear noise and signal distortion, which made high-speed optical transmission unreliable. However, by optimizing optical power distribution across wavelengths, KDDI has minimized interference and improved system efficiency.
The O-band offers advantages such as reduced wavelength dispersion and lower digital signal processing requirements, improving energy efficiency while ensuring high-speed and high-capacity communication. This breakthrough paves the way for more efficient and scalable fiber optic networks to support future 5G and post-5G communication systems.
SoftBank has been deploying advanced fiber-optic infrastructure to enable high-speed, low-latency connections. As the demand for ultra-reliable and high-capacity networks grows, SoftBank has leveraged fiber optics to enhance its 5G network, ensuring seamless connectivity for users across urban and suburban areas.
The deployment of dense fiber-optic networks has significantly reduced latency, a critical factor for applications such as real-time video streaming, cloud gaming, and industrial automation. Through fiber optics, SoftBank's 5G network can support gigabit-level speeds, improving the overall mobile experience for consumers and businesses alike.
SoftBank is also preparing for future advancements in mobile technology beyond 5G and 6G. As research progresses toward terahertz-based wireless communication, fiber-optic networks will remain essential in handling the enormous data loads associated with next-generation networks. SoftBank’s ongoing investment in fiber optics ensures that its 5G network remains not only robust but also future-proof, capable of supporting the evolving demands of an increasingly digital society.
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Broadband Milestones
In July 2024, Japan reached a historic milestone in telecommunications by setting a new global broadband speed record of 402 terabits per second (Tbps). This groundbreaking achievement was accomplished by researchers from the National Institute of Information and Communications Technology (NICT), who successfully transmitted data at this unprecedented speed using existing fiber-optic infrastructure.
This record-breaking speed was made possible through a first-of-its-kind optical transmission system that covers all transmission bands—O-, E-, S-, C-, L-, and U-bands—within the low-loss window of standard optical fibers. To accomplish this, the research team employed a combination of cutting-edge amplification technologies, including six different types of doped fiber optical amplifiers and both discrete and distributed Raman amplification. By integrating these techniques, the NICT was able to maximize the potential of fiber-optic transmission, pushing broadband speed capabilities far beyond existing global benchmarks.
The impact of this achievement is immense. At a speed of 402 Tbps, users could theoretically download 12,500 high-definition (HD) movies in just one second—a rate that surpasses the entire Netflix library multiple times over. This breakthrough has the potential to revolutionize how we access and use digital content, with profound implications for industries such as cloud computing, streaming and gaming, next-generation mobile networks, and scientific research. Faster data transmission could enhance real-time collaboration, enable lag-free virtual reality (VR) experiences, and accelerate large-scale artificial intelligence (AI) simulations.
While this record was achieved in controlled laboratory settings, researchers acknowledge that significant advancements and investments are required before such speeds can be realized in real-world scenarios. Expanding high-speed data transfer across long distances, including transoceanic fiber-optic networks, remains a challenge. Additionally, ensuring compatibility between ultra-high-speed systems and existing fiber infrastructure will be crucial in making this technology widely available.
To address these challenges, the NICT is committed to ongoing research and development in amplifier technology, fiber components, and novel transmission techniques. The institute also aims to expand the transmission bandwidth of ultra-high-capacity optical systems, ensuring their compatibility with commercially deployed fiber networks. These advancements will be critical in supporting the rapidly growing demand for global data services.
This achievement builds upon the NICT’s previous world record of 319 Tbps, set in 2021, showcasing Japan’s continuous leadership in pioneering next-generation telecommunications. With data consumption growing at an unprecedented rate, breakthroughs similar to this will be essential in shaping the future of global connectivity. As the NICT continues to push the boundaries of fiber-optic technology, the vision for ultra-fast, seamless global internet access is bound to be realized quicker than expected.
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