World’s First Standard Cladding Diameter 19-core Optical Fiber with Record Transmission Capacity

- Key technology for long-distance optical communication after Beyond 5G -

May 10, 2023
(Japanese version released on March 15, 2023)

National Institute of Information and Communications Technology
Sumitomo Electric Industries, Ltd.


  • An optical fiber with 19 cores within a standard cladding diameter was developed, enabling a transmission capacity of 1.7 petabits per second.
  • Randomly coupled multi-core fibers require less power consumption in the digital signal processing compared to multi-mode fibers.
  • This is a major step to realize future transoceanic-class long-distance, large-capacity optical communication systems.
A group of researchers from the National Institute of Information and Communications Technology (NICT, Japan) and Sumitomo Electric Industries, Ltd. (SEI, Japan) in collaboration with the Eindhoven University of Technology, University of L’Aquila, and Macquarie University has developed a 19-core optical fiber with a standard cladding diameter (0.125 mm), which has the largest number of cores among the standard cladding diameter multi-core fibers, and has demonstrated large-capacity transmission at a data-rate of 1.7 petabits per second over a distance of 63.5 km. A randomly coupled multi-core fiber design was used to achieve high core density, as well as a multiple input multiple output (MIMO) digital signal processing to eliminate inter-core signal interference. 
In this experiment, the world record was achieved for the transmission capacity of an optical fiber with a standard cladding diameter, and the world's longest transmission distance was achieved among transmission experiments with a capacity of 1 petabit per second or more. This result shows the possibility of significantly reducing the power consumption of MIMO digital signal processing in transoceanic systems, compared to multi-mode fiber transmission. This fiber technology will contribute to the realization of future long-distance and large-capacity optical communication networks. 
The results of this experiment were accepted as a post-deadline paper presentation at the 46th Optical Fiber Communication Conference (OFC 2023) and presented on Thursday, March 9, 2023.


Figure 1 Image of the developed 19-core optical fiber

Research on advanced optical fibers has attracted considerable attention to address ever-increasing traffic demands. NICT has achieved transmission capacities of 1.02 petabits per second for a standard cladding diameter uncoupled multi-core fiber, 1.53 petabits per second for a multi-mode fiber, and 0.17 petabits per second for a randomly coupled multi-core fiber (See Table 1).
However, in the case of an uncoupled multi-core fiber, the number of cores is limited to suppress signal interference between the cores, rendering an increase in capacity challenging. On the other hand, in the multi-mode fiber transmission, the propagation characteristics of each mode is significantly different, which poses a problem for long-distance transmission. Randomly coupled multi-core fiber overcomes these limitations by means of MIMO digital signal processing and is expected to be a transmission medium for future long-distance and large-capacity optical communication systems. Precise core placement is needed, however, and the maximum number of cores in a randomly coupled multi-core fiber with a standard cladding-diameter was 12.


In this research, SEI designed and fabricated a randomly coupled 19-core fiber with a standard cladding-diameter, and NICT constructed a transmission system to demonstrate the maximum capabilities of this fiber. In the experiment, 1.7 petabits per second of data were transmitted for 63.5 km. Optimization of the core structure and layout enabled this fiber to accommodate the world’s largest number of cores in a standard cladding diameter while achieving random coupling between cores (optical signal paths) and suppressing differences in propagation characteristics. Furthermore, Macquarie University has produced a three-dimensional laser-inscribed core multiplexer and demultiplexer, which can be used as an interface with conventional single-mode optical fibers.
To properly evaluate the transmission performance of randomly coupled multi-core fibers, it is necessary to receive signals from all cores and demodulate them simultaneously using MIMO processing. NICT constructed an optical transmission system that can simultaneously receive 19-core signals at a high symbol rate. Using commonly used wavelength bands (C and L bands) and polarization multiplexed 64QAM signals, NICT has demonstrated a total transmission capacity of 1.7 petabits per second over a transmission distance of 63.5 km. The difference in propagation time delay between optical signal paths is small, and the power consumption of signal processing can be greatly reduced.

Table 1 New optical fibers with a standard cladding diameter, and world records achieved by NICT.

In the “Beyond 5G” (6G) society, a cyber physical system supported by a large-capacity data communication infrastructure is required so that anyone can play an active role anywhere. On the other hand, to reduce the environmental impact, it is necessary to minimize the power consumption associated with data communications. Considering such social demands, the randomly coupled 19-core fiber in this study is one of the most promising candidates for the next-generation long-distance transmission medium.

Future Prospects

We will extend the transmission distance and expand the wavelength band to increase capacity, develop new devices compatible with the 19-core fiber, demonstrate advanced network functionalities such as switching, and investigate the feasibility of future deployment.
The results of this experiment were accepted as a post-deadline paper presentation at the 46th Optical Fiber Communication Conference (OFC 2023) and presented on Thursday, March 9, 2023.


International Conference: Optical Fiber Communication Conference (OFC 2023) Post-deadline Paper
Title: Randomly Coupled 19-Core Multi-Core Fiber with Standard Cladding Diameter
Authors: Georg Rademacher, Menno van den Hout, Ruben S. Luís, Benjamin J. Puttnam, Giammarco Di Sciullo, Tetsuya Hayashi, Ayumi Inoue, Takuji Nagashima, Simon Gross, Andrew Ross-Adams, Michael J. Withford, Jun Sakaguchi, Cristian Antonelli, Chigo Okonkwo, Hideaki Furukawa

Previous NICT Press Releases


1. Optical fiber transmission system

Figure 6 Schematic diagram of the optical fiber transmission system
Figure 6 shows a schematic diagram of the transmission system used for the evaluation of the 19-core fiber.
① Multi-wavelength light source: 381 carriers are generated in a single optical comb source.
② Signal modulation: Carriers are modulated with 64QAM signals and polarization multiplexed.
③ Transmission signal generation: Signals are branched for each core, and path delays are applied to emulate independent data streams.
④ Multi-core multiplexer: Each signal sequence is input to each core of the 19-core optical fiber through a waveguide-type multiplexer.
⑤ 19-core optical fiber: Signals propagate through a 63.5-km long 19-core fiber. 
⑥ Multi-core demultiplexer: Signal of each core on the receiving side is separated.
⑦ High-speed/parallel receiver circuit: The signals are wavelength-demultiplexed by filters and converted into electrical signals by coherent receivers.
⑧ Offline signal processing: MIMO processing eliminates signal interference during fiber propagation. 

2. Results of this experiment

In the experimental system shown in Figure 6, the transmission capacity (data-rate) of the system was estimated by directly applying error coding on the received bits. The blue dots in Figure 7 show the total data rate of all cores after applying error corrections with flexible overheads to maximize the throughput of each wavelength channel. Data rates of approximately 5 terabits per second in the C-band and 2.5 to 5 terabits per second in the L-band were obtained. The total transmission capacity of all wavelength channels was 1.7 petabits per second.

Figure 7 Summary of data-rate measurement results


Figure 2 Cross-section of a common standard single-mode optical fiber

Standard cladding diameter optical fiber

International standards specify that the outer diameter of the glass (cladding) of the optical fiber is 0.125 ± 0.0007 mm, and the outer diameter of the coating layer is 0.235 - 0.265 mm. The optical fiber widely used in current optical communication systems is a single-core single-mode fiber with a cladding diameter of 0.125 mm, and the transmission capacity is limited to approximately 250 terabits per second.

Figure 3 Conceptual images of optical fiber transmission schemes
[Click picture to enlarge]

Multi-core fiber

Standard single-core/single-mode optical fiber (see Figure 3(a)) has a capacity limit of approximately 250 terabits per second. To address this problem, multi-core fibers with increased number of cores (light paths) (see Figure 3(b)) and multi-mode fibers have been investigated. If the cores of a multi-core fiber are close to each other, the signal in one core leaks into the other cores, causing signal quality degradation due to interference (see Figure 3(c)). To suppress signal interference, core spacing of an uncoupled multi-core fiber is appropriately increased.

Randomly coupled multi-core fiber

Randomly coupled multi-core fiber (see Figure 3(d)) is a kind of multi-core fiber in which cores are densely arranged on the premise of eliminating signal interference between cores through MIMO digital signal processing. Compared to multi-mode fiber, randomly coupled multi-core fiber has uniform signal propagation characteristics in each core, making it suitable for long-distance transmission. However, to ensure the randomness of coupling between cores required for long-distance transmission, the core spacing must be strictly controlled.

Figure 4 Required number of multipliers per channel in MIMO digital signal processing versus transmission distance

MIMO digital signal processing

In the transmission using multi-mode fiber or randomly coupled multi-core fiber, MIMO processing for mode/core separation is almost inevitably required at the receiver side. MIMO is a signal processing technology for eliminating multipath interference in wireless communications. In optical communications, it is used to eliminate interference between various optical signals propagating in the same optical fiber.
The power consumption of MIMO processing depends mainly on the number of multipliers and is proportional to the length of the filter function to revert the effects of signal propagation in the fiber. In multi-mode fiber transmission, the length of the filter function depends on the propagation time difference of each mode, which generally increases in proportion to the fiber length. Therefore, the power consumption of digital signal processing required for long-distance transmission tends to be large. In randomly coupled multi-core fiber transmission, the propagation characteristics of each spatial channel (core) are uniform, and the length of the filter function is proportional to the square root of the transmission distance. Transoceanic-class (10,000 km) transmission systems using randomly coupled 19-core fibers will be able to reduce the number of multipliers per channel in MIMO processing by up to thousands compared to the case of 55-mode fibers (see Figure 4).

Multi-mode fiber transmission

A multi-mode fiber has a large core diameter, and multiple modes exist within the core (see Figure 3(e)). Inter-modal signal interference occurs during multi-mode fiber propagation, at the fiber connections, and also at the input/output. Therefore, it is important to eliminate the interference by using MIMO digital signal processing. Multi-mode fiber transmission of 55 modes at maximum was realized.

Figure 5 Mode-dependent propagation characteristics
[Click picture to enlarge]

Propagation characteristics for each mode

Multi-mode optical fiber generally has mode-dependent propagation loss and time delay. When the mode dependent loss is large, the quality of the signal deteriorates. When the propagation time delay difference is large, the power consumption required for MIMO digital signal processing becomes large.

Wavelength band

The wavelength bands used for telecommunication applications are the C band (wavelength 1,530 to 1,565 nm) and L band (1,565 to 1,625 nm); other bands include the O band (1,260 to 1,360 nm), E band (1,360 to 1,460 nm), S band (1,460 to 1,530 nm), and U band (1,625 to 1,675 nm). In this study, C-band and L-band were used.

Quadrature Amplitude Modulation (QAM) is a kind of multi-level modulation that uses both the phase and the amplitude of light to represent multiple bits. In 64QAM, each symbol can have 64 different phases and amplitudes in the complex plane and can represent 6-bit information (26 = 64).

Cyber physical system
In the “Beyond 5G” (6G) era, time and space will be controlled at a high level in both physical space and cyberspace, and the fusion of both spaces will make it possible to achieve things that could not have been achieved in physical space alone. Services that can be implemented across both physical space and cyberspace are expected to help solve various social issues. See for details.

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