March 28, 2025
First successful demonstration of a large-scale space-division multiplexed optical network consisting of a spatial cross-connect device and a multicore fiber optical amplifier
Kagawa University
KDDI Research, Inc.
NEC Corporation
Santec AOC Corporation
Furukawa Electric Co., Ltd.
Press Release Summary
Kagawa University (Headquarters: Takamatsu City, Kagawa Prefecture; President: Natsuo Ueda; hereinafter “Kagawa University”), KDDI Research, Inc. (Headquarters: Fujimino City, Saitama Prefecture; President and CEO: Hajime Nakamura; hereinafter “KDDI Research”), NEC Corporation (Headquarters: Minato-ku, Tokyo; President and CEO: Takayuki Morita; hereinafter “NEC”), Santec AOC Corporation (Headquarters: Komaki City, Aichi Prefecture; President and CEO: Noboru Uehara; hereinafter “Santec”), and Furukawa Electric Co., Ltd. (Headquarters: Chiyoda-ku, Tokyo; President and CEO: Hideya Moridaira; hereinafter “Furukawa Electric”) have established the fundamental technologies necessary for achieving a large-scale space-division multiplexed optical network.[1] They have also succeeded in the world's first demonstration experiment of a 1,000-km-class large-scale space-division multiplexed optical network consisting of a spatial cross-connect[2] device and a multicore fiber[3] optical amplifier[4], which is part of the results of their research. This is expected to be a major step towards opening the door for economical, ultra-high-capacity optical networks, which are essential for providing next-generation (Beyond 5G [6G]) wireless communication services[5]. Part of these results will be presented as one of the Top Scored papers at the Optical Fiber Communication Conference 2025 to be held in San Francisco, USA from March 30 to April 3, 2025.
This project was carried out based on the commissioned “Research and development of space-division multiplexed optical network node technology to support Beyond 5G ultra-high capacity wireless communications (JPJ012368C00201, JPJ012368C07801)” (principal researcher: Kagawa University) as part of the “Beyond 5G Research and Development Promotion Project” and “Innovative Information and Communications Technology (Beyond 5G (6G)) Fund[6]” of the National Institute of Information and Communications Technology (NICT) (Headquarters: Koganei City, Tokyo; President: Hideyuki Tokuda).
1. Press Release Details
(1) Background of the R&D Project
Currently, fifth generation (5G) wireless communication services are being introduced, and research and development for the next generation (Beyond 5G or 6G) of wireless communication services is already being implemented both in Japan and overseas. Future Beyond 5G (6G) wireless communication services aim to further enhance the 5G features of “high speed and large capacity,” “low latency,” and “massive connectivity. To achieve this, it is essential to build an economical, ultra-large capacity optical network that can handle petabits per second [7] (Pb/s) of traffic. Furthermore, as a foundation for supporting the AI society of the future, information and communication networks are expected to play an important role in connecting geographically distributed data centers and wireless base stations. As a new technology that enables this is considered to have great promise: a space-division multiplexed optical network consisting of uncoupled multicore fiber [8] (MCF), MCF optical amplifiers, and MCF optical switches. Research and development of long-distance space-division multiplexed transmission between two locations using 4-core fiber (4-CF) or 19-core fiber (19-CF) has been pursued thus far, but reports on the topic of space-division multiplexed optical networks using MCF have been limited to optical switches alone or small-scale network experiments.
(2) R&D Project Results
Now, an industry-academia collaborative research team consisting of Kagawa University, KDDI Research, NEC, Santec, and Furukawa Electric (PHUJIN Project[9]) has established the fundamental technologies (optical switch technology, optical wiring technology, optical amplification technology, optical node technology, optical network design and management technology) necessary for achieving a large-scale space-division multiplexed optical network, and successfully built next-generation optical node equipment and spatial cross-connect equipment using these technologies. Furthermore, by integrating these developed technologies, they succeeded in the world's first demonstration experiment of a large-scale space-division multiplexed optical network of at the 1,000 km level. Unlike current wavelength-division multiplexed networks that switch at a fine granularity of individual wavelength, space-division multiplexed optical networks use a low-loss core-selective switch[10] to switch at a coarse granularity of individual cores within an MCF. This is expected to enable ① reduction in transmission cost per bit, ② extension of transmission distance, and ③ reduction in the number of optical fiber connections inside optical node equipment.
Two space-division multiplexed optical network demonstration experiments were conducted as follows.
Long-distance recirculating optical network testbed (Figure 1):
In space-division multiplexed optical networks, MCF transmission systems using optical amplifiers without FIFO devices [11] can improve optical signal quality by eliminating the FIFO devices that cause additional loss, compared to conventional MCF transmission systems using single-core optical amplifiers and FIFO devices. This enables more data to be transmitted efficiently over longer distances. Furthermore, the introduction of low-loss spatial cross-connect [2] devices as MCF-compatible optical nodes that enable flexible path switching can further extend transmission distances while reducing costs. In this study, we built a long-distance recirculating optical network testbed for demonstration experiments consisting of a spatial cross-connect device using a core-selective switch [10], a FIFO-less four-core fiber amplifier [12], and a four-core fiber transmission line, and demonstrated for the first time that a large-scale space-division multiplexed optical network spanning a long distance of 1,600 km is feasible.
Figure 1. Long-distance space-division multiplexed optical network testbed
Multi-domain space-division multiplexed optical network testbed (Figure 2):
With advances in MCF design and manufacturing technologies, it is expected that multiple space-division multiplexed optical network domains (areas) built with MCFs of different core counts will coexist in the future. In this study, we interconnected a 4-core fiber network and a 16-core fiber network via a core selective switch-based spatial gateway device [10], and demonstrated for the first time that high-quality establishment and switching of spatial channels [13] is possible even in a large-scale multi-domain space-division multiplexed optical networks. The 4-core fiber network domain consists of a 4-core fiber link and a FIFO-less 4-core fiber amplifier [12], while the 16-core fiber network domain consists of a 19-core fiber link and a cladding-pumped [14] 19-core fiber amplifier (using only 16 cores).
(a) Testbed network configuration
(b) Panoramic view of the testbed
Figure 2. Multi-domain space-division multiplexed optical network testbed
The core technologies developed are as follows.
① Optical Node and Optical Network Technology (Kagawa University):
A spatial cross-connect (SXC) configuration method based on core-selective switches (CSS) with excellent device size scalability and connection flexibility, and a polarity management method for various MCF optical devices within the SXC [15] (Figure 3)
Figure 3. Optical node and optical network technology (Kagawa University)
② Optical Amplification Technology (KDDI Research, NEC, Furukawa Electric):
- A FIFO-less 4-core fiber amplifier (KDDI Research, Inc.) that enables low-noise optical amplification by injecting pump light into an erbium-doped 4-core fiber without passing through a spatial multiplexer/demultiplexer (fan-in/fan-out: FIFO[11]) (Figure 4)
- Omnidirectional 7-core fiber amplifier (NEC) that allows the propagation direction of the amplified optical signal to be set for each core (Figure 5)
- A cladding-pumped [15] 19-core fiber amplifier (Furukawa Electric) capable of simultaneously pumping all 19 cores (Figure 6)
Figure 4. Optical amplification technology: FIFO-less 4-core fiber amplifier (KDDI Research, Inc.)
Figure 5. Optical amplification technology: Omnidirectional 7-core fiber amplifier (NEC)
Figure 6. Optical amplification technology: Cladding-pumped 19-core fiber amplifier (Furukawa Electric)
③ Optical Switch Technology (Santec):
19-CF core-selective switch [10] (CCS) and 19-CF core selector [16] (CS) MCF optical devices (Figure 7)
Figure 7. Optical switch technology (Santec): 19-CF core-selective switch and 19-CF core selector
④ Optical Wiring Technology (Furukawa Electric):
MCF optical devices such as 19-CF cords/connectors with minimized higher-order modes, inter-core crosstalk, and bending loss, as well as 19-CF spatial multiplexers (fan-in/fan-out: FIFO) (Figure 8)
(3) Effects of the results
Future Beyond 5G (6G) wireless communication services aim to further enhance the 5G features of “high speed and large capacity,” “low latency,” and “massive connectivity.” To achieve this, it is essential to build an economical, ultra-large capacity optical network that can handle petabits per second (Pb/s) of traffic. This demonstration experiment of a large-scale space-division multiplexed optical network consisting of a spatial cross-connect device and a multicore fiber optical amplifier s is expected to be a major step towards opening the door for economical, ultra-high-capacity optical networks, which are essential for providing next-generation (Beyond 5G [6G]) wireless communication services.
Figure 8. Optical wiring technology (Furukawa Electric): 19-CF spatial multiplexer (FIFO)
2. Explanation of Terms
1. Space-division multiplexed optical network:
In current optical networks, optical signals that are wavelength-multiplexed in optical fibers are routed on a wavelength-by-wavelength basis at optical nodes. In space-division multiplexed optical networks, optical signals propagated by space-division multiplexing using the multiple cores of multicore fibers are routed on a core-by-core basis at spatial cross-connect devices. By routing on a core-by-core basis, which is a larger granularity than wavelength-by-wavelength basis, space-division multiplexed optical networks are expected to enable ultra-large-capacity optical networks that are economical.
2. Spatial cross connect (SXC) equipment:
This is a type of optical node that has multicore fibers (MCF) installed at the input and output ports, and routes optical signals propagated by space-division multiplexing using the multiple cores of multicore fiber (Explanation of Terms [2]) on a core-by-core basis according to their destination. By building it using a core-selective switch (CSS) described in the Explanation of Terms [10], it is expected that a low-loss and low-cost SXC will be achieved.
3. Multi-core fiber (MCF):
The optical fibers currently in use have only one optical path, called a core, inside a hair-thick glass fiber. Multicore fibers have multiple cores inside a single optical fiber, and it is expected that the transmission capacity per optical fiber will increase significantly (by a factor of the number of cores).
4. Optical Amplifier:
A device that amplifies the power of an optical signal that has decreased as it passes through an optical transmission line. The optical amplifier used in this experiment was an erbium-doped fiber amplifier (EDFA), which amplifies an optical signal by inputting pump light of a specific wavelength shorter than the optical signal wavelength, along with the optical signal, into the core of an optical fiber doped with erbium ions.
5. Beyond 5G (6G) wireless communication services:
In addition to further enhancing the features of fifth-generation wireless communication services (5G) (high speed, large capacity, low latency, and massive connectivity), Beyond 5G wireless communication services are also expected to boast features such as an expansion of usage areas to include sky, sea, and space, in addition to ultra-low power performance and ultra-high reliability. “Beyond 5G” wireless communication services are also known as sixth-generation (6G) wireless communication services.
6. Innovative Information and Communications Technology (Beyond 5G (6G)) Fund:
https://b5g-rd.nict.go.jp NICT “Innovative Information and Communication Technology (Beyond 5G (6G)) Fund Homepage”
7. Petabits per second:
Petabit (“P”) is a prefix used before units and stands for 10 to the 15th power. One petabit per second (Pb/s) means transmitting 10 to the 15th power bits of digital data per second.
8. Uncoupled Multicore Fiber (Uncoupled MCF):
A multicore fiber in which the coupling of optical power between the multiple cores arranged within it is extremely small, and each core can in fact be considered an independent optical transmission path.
9. PHUJIN Project:
https://phujin-project.jp
10. Core-selective switch (CSS):
A 1✕N optical device with MCFs placed at input and output ports. Any core in the input MCF port can be output to any core with the same number in any output MCF port.
11. FIFO (Fan-in/Fan-out):
An optical device that spatially multiplexes and demultiplexes each core in a multicore fiber into the corresponding number of single-mode fibers.
12. FIFO-less 4-core fiber amplifier:
Four-core fiber amplifier features an optical coupler that utilizes side polishing of the four-core fiber to inject pump light into an erbium-doped four-core fiber. This avoids excess loss due to FIFO (fan-in/fan-out) (see Explanation of Terms [11]), making it possible to achieve low-noise optical amplification.
13. Spatial channels:
A physical communication path for optical signals established by connecting the cores in each MCF link on the route from the transmitting station to the receiving station with an SXC.
14. Cladding pumping:
This is an excitation method in which a double-clad structure is used for the erbium-doped multi-core fiber (MC-EDF), with a polymer cladding and coating on the outside of a glass cladding, and a tapered multimode fiber is wrapped around the MC-EDF, thereby coupling the excitation light generated by a multimode semiconductor laser to each core of the MC-EDF.
15. Polarity of a Multi-Core Fiber (MCF):
The arrangement of cores at each end of a multicore fiber (MCF) is reversed left to right.
16. Core Selector (CS):
An optical device with an input MCF port and an output single-mode fiber (SMF). The core of the input SMF can be output to any core in the output MCF. When used together with a core-selective switch (CSS) (see Explanation of Terms [10]), it can achieve a highly flexible spatial cross-connect device (see Explanation of Terms [1]) that can connect a client optical signal to any core of a multicore fiber link in any direction.
3. Lecture paper
(1)
Title: “Core-level Routing in Long-haul MCF Transmission System with FIFO-less Multicore EDFA and Spatial Cross-connect” (Top Scored)
Authors: 1Kosuke Komatsu, 1Shohei Beppu, 1Daiki Soma, 1Yuta Wakayama, 1Noboru Yoshikane, 2Masahiko Jinno, 1Takehiro Tsuritani
Affiliation: 1KDDI Research, Inc., 2Kagawa University, Presentation number: M3F.1
Date and time: Monday, March 31, 2025
International Conference: Optical Fiber Communication Conference (OFC) 2025
(2)
Title: “Demonstration of 4-Core/16-Core Fiber Heterogeneous Spatial Channel Network Comprising 19-Core Fiber Core Selective Switch-Based Spatial Gateway, 4-Core EDFAs, and 19-Core EDFAs”
Authors: 1Takumi Tani, 2Daiki Soma, 3Ryohei Otowa, 4Yusuke Matsuno, 1Kyosuke Nakada, 2Kosuke Komatsu, 3Yuji Hotta, 4Tsubasa Sasaki, 1Rika Tahara, 2Shohei Beppu, 4Koichi Maeda, 1Takuma Izumi, 2Yuta Wakayama, 2Noboru Yoshikane, 2Takehiro Tsuritani, 3Yasuki Sakurai, 4Ryuichi Sugizaki, and 1Masahiko Jinno
Affiliation: 1 Kagawa University, 2 KDDI Research, Inc., 3 Santec AOC corporation, 4Furukawa Electric Co., Ltd.
Presentation number: M3F.2
Date and time: Monday, March 31, 2025
International Conference: Optical Fiber Communication Conference (OFC) 2025
Inquiries regarding this matter:
Kagawa University
Masahiko Jinno, Professor, Division of Electrical and Information Engineering, Faculty of Engineering and Design
Tel: 087-864-2242
Email: jinno.masahiko@kagawa-u.ac.jp
Tsuneko Fujiwara, General Affairs Division, Hayashi-cho Regional Integrated Administrative Center
Tel: 087-832-2034
E-mail: fujihara.tsuneko@kagawa-u.ac.jp
KDDI Research, Inc.
Corporate Promotion Department
URL: https://www.kddi-research.jp/inquiry.html
NEC Corporation
Global Innovation Strategy Department
URL: https://jpn.nec.com/cgi-bin/cs/opinion_form4.cgi
Santec Holdings Corporation
Business Management Headquarters, Business Strategy Group
URL: Santec
Furukawa Electric Co., Ltd.
Public Relations Department, Murakoshi
Email: fec.pub@furukawaelectric.com
