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389.3-Tb/s 1017-km C-band Transmission over Field-Installed 12-Coupled-Core Fiber Cable with >12-Tb/s Spatial MIMO Channels

This paper demonstrates a record-breaking 389.3-Tb/s transmission over 1,017 km of field-installed 12-coupled-core fiber, achieving a 0.455-Pb/s coupled-core capacity and over 12 Tb/s per spatial MIMO channel.

Original authors: Akira Kawai, Kohki Shibahara, Megumi Hoshi, Masanori Nakamura, Takayuki Kobayashi, Ryota Imada, Takayoshi Mori, Taiji Sakamoto, Yusuke Yamada, Kazuhide Nakajima, Munehiko Nagatani, Hitoshi Wakita, Yut

Published 2026-04-02

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Akira Kawai, Kohki Shibahara, Megumi Hoshi, Masanori Nakamura, Takayuki Kobayashi, Ryota Imada, Takayoshi Mori, Taiji Sakamoto, Yusuke Yamada, Kazuhide Nakajima, Munehiko Nagatani, Hitoshi Wakita, Yuta Shiratori, Hiroshi Yamazaki, Hiroyuki Takahashi, Soichi Endo, Takemi Hasegawa, Ryo Nagase, Yutaka Miyamoto

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the internet as a massive highway system. For decades, we've been trying to add more lanes to this highway to carry more data (cars). Usually, we just make the existing lanes wider or faster. But there's a limit to how wide a single lane can get before it becomes unstable.

This paper describes a breakthrough where researchers didn't just widen the lanes; they built a 12-lane super-highway inside a single pipe and successfully drove a record-breaking amount of data through it over a real-world, bumpy road.

Here is the breakdown of what they did, using simple analogies:

1. The "12-Lane Tunnel" (The Fiber Cable)

Think of a standard fiber optic cable as a single-lane tunnel. To carry more data, scientists have been trying to pack multiple tunnels inside one standard-sized pipe. This is called Space-Division Multiplexing (SDM).

In this experiment, the team used a special "12-Coupled-Core" fiber.

The Analogy: Imagine a single straw that actually contains 12 smaller straws inside it, all glued together.
The Twist: These 12 straws aren't isolated; they are "coupled," meaning the light in one straw can gently talk to the light in its neighbors. This is like having 12 lanes on a highway where cars can smoothly switch lanes to avoid traffic jams. This "coupling" actually helps stabilize the signal over long distances.

2. The "Field Test" (The Real Road)

Most previous records were set in a laboratory—a perfectly smooth, climate-controlled track with no potholes.

The Challenge: This team took their 12-lane super-highway and laid it in the real world. They used a cable that was already buried underground and strung up on poles (aerial sections).
The Obstacles: Real cables have "splices" (where two cables are joined) and "connectors" (where cables plug into equipment). These are like construction zones or toll booths on a highway. Usually, these spots cause data to get lost or scrambled.
The Result: They successfully sent data through 19 of these "construction zones" over a distance of 1,017 kilometers (about 630 miles).

3. The "Super Fast Cars" (The Data)

They didn't just send a few cars; they sent a massive convoy.

The Speed: They used a signal speed of 140 Gbaud. Think of this as the engine revving incredibly fast.
The Cargo: They packed the data using a complex format (PS-QAM) that is like a highly efficient cargo container, squeezing more information into every single "car."
The Volume:
- Over a short distance (53.5 km), they moved 455 Terabits of data. That's like downloading every movie ever made in a few seconds.
- Over the long distance (1,017 km), they still managed 389 Terabits.

4. The "Traffic Cop" (The MIMO Processor)

Because the 12 lanes are "coupled" (neighbors talking to each other), the data gets mixed up as it travels. By the time it reaches the end, the signal from Lane 1 might be slightly mixed with Lane 2.

The Solution: They used a 96x24 MIMO processor.
The Analogy: Imagine a chaotic parking lot where 12 cars arrive, but their passengers have mixed up their luggage. A super-smart traffic cop (the MIMO algorithm) looks at the entire mess and instantly sorts out which luggage belongs to which car, reconstructing the original message perfectly. This "digital magic" allowed them to keep the lanes tightly packed without the data getting garbled.

5. Why This Matters

Before this, we knew 12-lane fibers worked in a lab, but we didn't know if they could survive a real-world installation with all its bumps, joins, and connectors.

The Verdict: They proved it works. The "traffic cop" (the computer processing) was stable enough to handle the real-world noise.
The Future: This paves the way for the next generation of the internet. Instead of laying thousands of new cables (which is expensive and disruptive), we can upgrade existing infrastructure to carry Petabit-class speeds (1,000 Terabits).

In a nutshell:
They took a complex, 12-lane data highway, drove it over a bumpy, real-world road for 600 miles, and proved that with the right "traffic control" software, we can move more data than ever before without building new roads. This is a giant leap toward the future of ultra-fast global internet.

1. Problem Statement

The rapid growth of data traffic necessitates optical transmission systems with ultra-high capacity. Space-division multiplexing (SDM), specifically using Coupled-Core Multicore Fibers (CC-MCF), offers a pathway to increase capacity by utilizing multiple spatial degrees of freedom within a standard cladding diameter. However, two critical challenges have hindered the deployment of CC-MCF in real-world terrestrial networks:

Field Validation: Previous high-capacity demonstrations were largely confined to laboratory settings. There was a lack of validation regarding the feasibility of high-capacity transmission in field-installed cables, which involve numerous connection points (splices and connectors) and varying environmental conditions.
High-Speed Signal Processing: While laboratory experiments have achieved high capacities, there was a need to demonstrate fully spatially coupled Multiple-Input/Multiple-Output (MIMO) transmission using broadband signals exceeding 100 Gbaud over long distances (>1000 km).

2. Methodology and Experimental Setup

The authors conducted a transmission experiment over a field-installed 12-coupled-core fiber (12CCF) cable.

Fiber Infrastructure:
- Cable Type: A 12-coupled-core fiber cable with a standard cladding diameter, installed in a real-world environment.
- Installation: The cable included a ~0.2 km aerial section and ~4.1 km of underground tunnel sections.
- Transmission Line: A 53.5 km span was constructed by interconnecting 11 fibers within the cable using MCF splicing and SC-standard MCF connectors. The total transmission distance tested was 19 spans (1017 km).
- Fiber Characteristics: The fiber exhibited low Spatial Mode Dispersion (SMD) of <6 ps/km $^{1/2}$ across the C-band and met G.652.D bending loss standards.
Transmitter and Signal Generation:
- Modulation: 140-Gbaud Probabilistically Shaped (PS) QAM signals (specifically PS-36QAM derived from PS-64QAM).
- Hardware: Utilized a 4-channel 32 GHz CMOS DAC-based Arbitrary Waveform Generator (AWG) and broadband InP-DHBT bandwidth doublers to achieve the high symbol rate.
- WDM: 31 wavelength channels were used across a 4.65 THz bandwidth (150 GHz grid).
- Power: Input power was 20.0 dBm per core (30.8 dBm total).
Recirculating Loop and Reception:
- Loop Configuration: The signal entered 12 parallel recirculating loops interfaced with the transmission line via fan-in/fan-out devices.
- Reception Architecture: An SDM-TDM (Space-Division Multiplexing / Time-Division Multiplexing) configuration was employed. A single high-speed coherent receiver (70 GHz) processed the 12-core multiplexed signals.
- Digital Signal Processing (DSP):
  - Offline processing included chromatic dispersion compensation.
  - MIMO Equalization: A frequency-domain complex 96×24 MIMO adaptive equalizer (FFT size 2048) was used to handle the spatial coupling.
  - Decoding: Adaptive coding with Forward Error Correction (FEC) was applied, constructing FEC frames across all spatial channels to mitigate Mode-Dependent Loss (MDL).

3. Key Contributions

First Field Demonstration: This is the first report of transmission experiments over a field-installed 12CCF cable containing multiple splicing and connector points.
Record Capacity in Field Environment: Achieved a net capacity of 389.3 Tb/s over 1017 km and 455.4 Tb/s over a single span (53.5 km) in a terrestrial field setting.
High Spectral Efficiency per Channel: Demonstrated spatial MIMO channels with net bitrates exceeding 12 Tb/s per wavelength (average 12.55 Tb/s over 19 spans).
Validation of Stability: Proved that key transmission parameters (memory length and MDL) remain stable over time and frequency in a field environment, even with complex connection points.

4. Experimental Results

Capacity Metrics:
- Single Span (53.5 km): Net bitrate of 455.4 Tb/s (Achievable: 465.8 Tb/s). Average per-wavelength bitrate: 14.69 Tb/s.
- Multi-Span (1017 km, 19 spans): Net bitrate of 389.3 Tb/s (Achievable: 409.0 Tb/s). Average per-wavelength bitrate: 12.55 Tb/s.
- Coupled-Core Capacity: Achieved a record 0.455 Pb/s coupled-core capacity in a field environment.
Transmission Characteristics:
- Memory Length ( $\tau_m$ ): The impulse response width was limited to 2.1 ns even at 1017 km, fitting the theoretical model for strongly coupled cores ( $\tau_m \propto \sqrt{L}$ ).
- Mode-Dependent Loss (MDL): The root-mean-square MDL ( $\sigma_{rms}$ ) was estimated at 0.35 dB per span.
- Stability: 1-hour measurements at 428 km showed high stability, with $\tau_m$ averaging 1.34 ns and $\sigma_{rms}$ averaging 1.98 dB, with very low standard deviations. This confirms the robustness of the system against temporal fluctuations.
Uniformity: The performance was uniform across the entire C-band (191.5–196.5 THz), with standard deviations for $\tau_m$ and $\sigma_{rms}$ being 0.07 ns and 0.12 dB, respectively.

5. Significance

This work represents a major milestone in the commercialization of SDM technology. By successfully demonstrating sub-petabit class total capacity and 10 Tb/s-class channel capacity over a field-installed cable with standard cladding, the authors have validated the feasibility of deploying CC-MCF in future terrestrial high-capacity networks. The results confirm that the challenges of fiber nonlinearity, spatial-mode dispersion, and connection-induced impairments can be effectively managed using advanced MIMO DSP and high-speed hardware, paving the way for the next generation of optical infrastructure.