Japan is advancing long-distance optical cable technology using multicore fibers, including experiments with 12-core and higher-core fibers to increase transmission capacity for submarine and terrestrial networks.

Overview of Multicore Fiber Development in Japan

Japan has been at the forefront of multicore optical fiber research, aiming to enhance the capacity of long-distance and transoceanic communication systems. Traditional optical fibers use a single core for signal transmission, but multicore fibers contain multiple cores within the same fiber cladding, allowing simultaneous transmission of multiple optical signals without increasing the fiber diameter . This approach significantly boosts data throughput while maintaining compatibility with existing infrastructure.

Long-Distance Experiments

• 12-Core Fiber Transmission: NEC and NTT successfully conducted a 7,280 km transoceanic-class transmission experiment using a coupled 12-core multicore fiber. Each core carried independent optical signals, and advanced signal processing techniques, including MIMO algorithms, were used to mitigate crosstalk between cores . This experiment demonstrates the feasibility of high-capacity long-haul optical networks for future submarine cables.
• 19-Core Fiber Transmission: The National Institute of Information and Communications Technology (NICT) and Sumitomo Electric achieved 1.02 petabits per second over 1,808 km using a 19-core fiber. This represents a world record for long-distance, high-capacity optical transmission and highlights the potential for scaling multicore fiber technology to meet growing global data demands .

Technical Considerations

• Crosstalk Management: As the number of cores increases, optical signals can leak between adjacent cores, causing interference. Japanese researchers have developed coupled multicore fibers and advanced demodulation techniques to minimize this effect .
• Optical Amplification: Long-distance transmission requires optical amplification systems compatible with multicore fibers to maintain signal integrity over thousands of kilometers .
• Capacity Scaling: Multicore fibers allow for higher data rates without increasing the fiber diameter, making them suitable for submarine cables where space and weight are critical .

Applications and Future Prospects

While specific 6-core fibers are not explicitly mentioned in the latest experiments, Japan's ongoing R&D in multicore fibers with 2, 4, 12, and 19 cores indicates that 6-core fibers could be implemented for regional or long-haul networks where intermediate capacity is required. These fibers are expected to support:

• High-capacity submarine cables connecting Asia-Pacific regions
• Data center interconnects for 5G and cloud services
• Next-generation optical networks with scalable bandwidth Japan's multicore fiber initiatives aim to increase transmission capacity by several times compared to conventional single-core fibers, with laboratory demonstrations showing potential capacities exceeding 1.7 petabits per second over 3,000 km-class submarine cables . In summary, Japan is actively developing long-distance multicore optical cables, with 12-core and 19-core fibers demonstrating world-class transmission performance. While 6-core fibers are not specifically highlighted, the technology and infrastructure being developed make them a feasible option for high-capacity optical networks in the near future.