• A world record transmission of 1 petabit per second in a multimode optical fiber increases the current record data rate in multimode optical fibers by more than 2.5 times.
  • Wideband optical transmission in fibers with more 15 modes is demonstrated for the first time, enabled by mode multiplexers and a transmission fiber optimized for high optical bandwidth.
  • This demonstration advanced high-density and large capacity transmission in optical fibers that can be produced with standard methods.
A group of researchers from the Network System Research Institute of the National Institute of Information and Communications Technology (NICT, Japan) led by Georg Rademacher, NOKIA Bell Labs (Bell Labs, USA) led by Nicolas K. Fontaine and Prysimian Group (Prysimian, France) led by Pierre Sillard succeeded in the world’s first transmission exceeding 1 petabit per second in a single-core multi-mode optical fiber. This increases the current record transmission in a multi-mode fiber by a factor of 2.5.
To date, transmission experiments in optical fibers supporting large number of modes was limited to small optical bandwidths. In this study, we demonstrated the possibility of combining highly spectral efficient wideband optical transmission with an optical fiber guiding 15 fiber modes that had a cladding diameter in agreement with the current industry standard of 0.125 mm. This was enabled by mode multiplexers and an optical fiber that supported wideband transmission of more than 80 nm over a distance of 23 km. The study highlights the large potential of single-core multi-mode fibers for high capacity transmission using fiber manufacturing processes similar to those used in the production of standard multi-mode fibers. 
The results of this study were accepted for the post-deadline session at the 46th European Conference on Optical Communication (ECOC 2020).


Over the past decade, intensive research was carried out worldwide to increase the data rates in optical transmission systems using space-division multiplexing in order to accommodate the exponentially increasing data transmission requirements. Compared to multi-core optical fibers, multi-mode fibers can support a higher spatial-signal-density and are easier to manufacture. However, using multi-mode fibers for high capacity space-division multiplexed transmission requires the use of computationally intensive digital signal processing. These requirements increase with the number of transmission modes and realizing transmission systems supporting large number of fiber modes is an active field of research. 


Figure 1
Figure 1: Previous high capacity demonstrations in multi-mode fibers
At NICT, a transmission experiment was designed and carried out that utilized the transmission fiber made by Prysmian and mode multiplexers developed by Bell Labs.  A wideband transceiver subsystem was developed at NICT to transmit and receive several hundred highly spectral efficient WDM channels of high signal quality. The novel mode multiplexers were based on a multi-plane light conversion process where the light of 15 input fibers was reflected multiple times on a phase plate to match the modes of the transmission fiber. The transmission fiber was 23 km long and had a graded-index design. It was based on existing multi-mode fiber designs that were optimized for wideband operation and had a cladding diameter of 0.125 mm and a coating diameter of 0.245 mm, both adhering to the current industry standard. The transmission system demonstrated the first transmission exceeding 1 petabit per second in a multi-mode fiber increasing the current record demonstration by a factor of 2.5.
Figure 2
Figure 2: Experimental setup
When increasing the number of modes in a multi-mode fiber transmission system, the computational complexity of the required MIMO digital signal processing increases. However, the used transmission fiber had a small modal delay, simplifying the MIMO complexity and maintained this low modal delay over a large optical bandwidth. As a result, we could demonstrate the transmission of 382 wavelength channels, each modulated with 64-QAM signals. The success of large-capacity transmission using a single-core multimode optical fiber, which has a high spatial signal density and easy manufacturing technology, is expected to advance high-capacity multimode transmission technology for future high capacity optical transmission systems.

Future Prospects

In the future, we would like to pursue the possibility of extending the distance of large-capacity multi-mode transmission and integrating it with multi-core technology to establish the foundation of future optical transmission technology with large capacity.
The paper on the results of this experiment was published at the 46th European Conference on Optical Communication (ECOC2020, December 6th - 10th 2020), which is one of the largest international conferences related to optical fiber communication. It was planned to be held in Brussels, Belgium but had to be conducted virtually due to the Novel Corona Virus epidemic. The paper received a very high evaluation from and was adopted for presentation in a special session for the latest research (Post Deadline Paper) that took place on the 10th of December.


International Conference: European Conference on Optical Communication (ECOC2020)
Post Deadline Paper
Title: 1.01 Peta-bit/s C+L-band transmission over a 15-mode fiber
Authors: Georg Rademacher, Benjamin J. Puttnam, Ruben S. Luís, Tobias A. Eriksson, Nicolas K. Fontaine,  Mikael Mazur, Haoshuo Chen, Roland Ryf, David T. Neilson, Pierre Sillard, Frank Achten, Yoshinari Awaji, and Hideaki Furukawa

Previous NICT Press Releases


1. Description of the novel transmission system

Figure 5
Figure 5: Schematic of the optical transmission setup
① 382 carrier lines are generated in a single optical comb source
② 15 x 382 carrier lines are modulated with 64 QAM signals
③ Each of the 15 signal combs are launched into a different fiber mode
④ Wavelength filters extract one WDM channel from all fiber modes
⑤ MIMO processing is performed taking into account the signals from all 15 fiber modes

2. Experimental Results

Data rate for all 382 WDM channels.
Figure 6: Data rate for all 382 WDM channels.
The experimental setup in Figure 5 was used to measure the performance for each WDM channel. As performance varied for different wavelength channels, flexible overheads were assumed to maximize the throughput for each wavelength channel.
Figure 6 shows the data rate for all 382 WDM channels after implementing forward error correction. When summing up the data rates for all wavelength channels, a total data rate of 1.01 petabit/s is achieved.


1 petabit is 1000 trillion bits, 1 terabit is 1 trillion bits, and 1 gigabit is 1 billion bits. One petabit per second is equivalent to 10 million channels of 8K broadcasting per second.
15 mode fiber
Figure 3:
Figure 3: Cross section of the 15 mode multi-mode fiber
The transmission fiber had a cross section as shown in Figure 3 with a core diameter of 0.028 mm and a standard cladding diameter of 0.125 mm. The fiber was designed to allow the propagation of 15 fiber modes while cutting off any fiber modes of higher order. The fiber was designed to minimize the propagation delay difference between all 15 fiber modes. 
previous transmission demonstrations with multi-mode fibers
To date transmission has been demonstrated with up to 45 fiber modes. The current record data rate was reported at 0.4 petabit per second in a 10 mode multi-mode fiber.
wideband WDM technology
Using a single optical comb source, signals were carried at different wavelength channels. This technology is called wavelength division multiplexing (WDM) and for this transmission experiment, two wavelength bands, called the C- and the L-band were used.
mode multiplexer based on multi-plane light conversion
 Figure 4:
Figure 4: Broadband mode multiplexer
Transmitter and receiver sub-systems are largely based on single-mode fiber technology. Therefore, a novel device is necessary that can convert the signal from 15 input signals to be compatible with the 15 modes, guided by the multi-mode fiber. In this experiment, a novel wideband mode multiplexer was employed that was based on reflecting the light from 15 input fiber multiple times on a phase plate to generate signals that are compatible with the 15-mode fiber.
MIMO (Multiple-input-multiple-output) digital signal processing
MIMO is a signal processing technology that was originally used in wireless communications to eliminate multi-path interference. In optical communications, MIMO is a signal processing technology to remove inteference between signals that propagate in the same fiber core. The complexity of MIMO processing increases with the number of fiber modes and if the propagation speed difference of all fiber modes increases. 
64 QAM (Quadrature amplitude modulation)
QAM is a multi-level modulation format with high spectral information density. 64 QAM uses 64 different signal symbols and can therefore encode 6 bit of information. The spectral density of 64 QAM is therefore 6 times higher than for simple modulation formats such as on-off keying. However, using modulation formats such as 64-QAM makes the system more vulnerable to signal distortions such as optical amplifier noise.

Technical Contact

AWAJI Yoshinari, FURUKAWA Hideaki
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