Demonstration of World Record Transmission Capacity in a Single Optical Fiber over a 38-core 3-mode Optical Fiber | National Institute of Information and Communications Technology

Points

Transmission of 10.66 Pb/s with a spectral efficiency of 1158.7 bit/s/Hz over a 38-core 3-mode fiber
A low-DMD, high core-count few-mode fiber, adoption of 256- and 64-QAM modulation
Drastic increase of data-rate per fiber for intra- and inter data-center communication

The National Institute of Information and Communications Technology (NICT, President: TOKUDA Hideyuki, Ph.D.), Sumitomo Electric Industries, Ltd. (Sumitomo Electric, President: INOUE Osamu) and Optoquest Co., Ltd. (Optoquest, President: HIGASHI Noboru) succeeded in experimental transmission at 10.66 peta-bit per second, achieving a spectral efficiency of 1158.7 bits per second/Hz. This result exceeded the previous record of 10.16 peta-bit per second.

In this experiment, we develop an optical fiber that supports the transmission of three transverse modes in 38 cores with reduced relative propagation delays between modes, and demonstrated its suitability for high spectral efficiency modulation, namely 256- and 64-quadrature amplitude modulation (QAM). The achieved data rate per fiber increased by a factor of more than 100 over existing commercial transmission systems, demonstrating a potential to significantly reduce the number of fibers required for data transmission over short distances, such as intra- and inter data-center traffic. This result will be presented at the Optical Fiber Communication Conference （OFC 2020） to be held on March 8-12, 2020, in San Diego）.

Background

In 2008, NICT established a study group on Extremely Advanced Optical Transmission Technologies to enhance collaboration between industry, universities and the government, engaging in pioneering research and development. The research by the collaborative group is at a high level in fierce global competition, exemplified by a past data-rate demonstration record of 10.16 peta-bit per second in a 19-core 6-mode fiber. To achieve larger capacities, a fiber with a larger number of cores or modes is required. However, there are several technical challenges in increasing them, such as the mechanical reliability of fibers or the complexity of signal processing.

Achievements

For this transmission experiment, Sumitomo Electric developed a 38-core 3-mode fiber, Optoquest developed a 38-core multiplexer, and NICT performed a transmission experiment of 10.66 peta-bit per second over 13 km distance.

Figure 1: Results of this project in comparison to previous research efforts of NICT

When transmitting different data-streams over different transverse modes in each core, the signals typically experience strong mixing and require digital signal processing (DSP) to separate the signals at the receiver. To reduce the complexity of the DSP, it is important to reduce the propagation delay differences between the modes (DMD: Differential Mode Delay). For this experiment, we fabricated a 38-core 3-mode fiber with reduced propagation delays between modes in each core for simplifying DSP and achieved a delay difference of 0.6-3.0 nanoseconds. Furthermore, loss variation between different modes (MDL: Mode-Dependent Loss), can impair signal quality and reduce achievable data-rate. In the experiment, both the optical fiber and the core- and mode-multiplexers were optimized for a reduced MDL of 5-8.5 dB for most of the fiber cores. Depending on the MDL and DMD in each core, highly spectrally efficient modulation formats of 256- and 64-QAM were selected for transmission leading to data-rates between 279 tera-bit per second and 298 tera-bit per second in each of the 38 cores.

Due to the transmission of a total of 114 spatial channels (38 cores x 3 modes), we increased the transmission capacity by a factor of more than 100 compared to the current standard transmission systems and hence these results demonstrate a potential to significantly reduce the number of fibers required in short-range, ultra-high-capacity systems, such as those for intra- and inter data-center connections.

Future Prospects

NICT will continue to promote the effort for early social implementation of the technologies, and the cutting-edge/innovative research and development toward the realization of the ultimate performance of the multi-core/multi-mode optical fiber transmission systems.

References

International conference: The Optical Fiber Communication Conference (OFC 2020)

Title: 10.66 Peta-Bit/s Transmission over a 38-Core-Three-Mode Fiber

Authors: Georg Rademacher, Benjamin J. Puttnam, Ruben S. Luis, Jun Sakaguchi, Werner Klaus, Tobias A. Eriksson, Yoshinari Awaji, Tetsuya Hayashi, Takuji Nagashima, Tetsuya Nakanishi, Toshiki Taru, Taketoshi Takahata, Tetsuya Kobayashi, and Naoya Wada

Previous NICT and Sumitomo Electric Press Releases

Appendix

1. Experimental System Demonstration

Figure 4: Optical Multiplexing Techniques

Figure 4 shows the applied optical multiplexing techniques. 368 independent wavelengths are used to carry with 64- or 256-quadrature amplitude modulated data. As optical amplifiers have a limited bandwidth, the 368 wavelength channels are separated into two regions, considered as C and L bands. Each of the three fiber modes carries 368 wavelength channels, and each of the 38 fiber cores transports the three transverse modes.

Figure 5: Schematic of the experimental setup

Figure 5 shows the experimental setup used for this demonstration. A single optical comb source produces the 368 laser lines used for wavelength multiplexing. A modulator setup modulates those laser lines with 64- or 256-QAM signals. Decorrelated copies are produced for each of the 38 x 3 = 114 different spatial channels. Spatial multiplexing is performed in two stages: first to generate few-mode signals in mode multiplexers and second to launch into the respective core in core-multiplexers. The inverse sequence is performed after the fiber. The signal performance is measured in a coherent receiver setup.

2. Experimental Results

Figure 6: Data-rate for each wavelength channel in all 38 cores.
The number corresponds to the total data-rate that was transmitted in each core.

Figure 6 shows the results of the experiment. A data rate was measured for each wavelength channel in each core. The data rates were between 180 and 298.20 Tb/s for all fiber cores. The total aggregated data rate corresponds to 10.66 Pb/s.

Glossary

Pb/s

1 peta-bit/s (Pb/s) corresponds to 1,000 tera-bit/s or 1,000,000 giga-bit/s. 1 Pb/s corresponds to 10,000,000 8K broadcasting channels.

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spectral efficiency

An indicator for the amount of information that is carried in a certain spectrum, indicating efficient transmission.

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previous world record of 10.16 Pb/s (Spectral efficiency: 1099.9 bit/s/Hz)

Record by KDDI and Sumitomo Electric in September 2017

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256 QAM (quadrature amplitude modulation), 64 QAM

QAM is a method to encode data in the phase and amplitude of light.

256-QAM uses 256 different constellation points, allowing transmission of 8 bit per symbol (time-slot), in comparison to traditional modulation formats such as OOK (on-off keying) that can only transmit 1 bit/symbol.

64-QAM uses 64 different constellation points, allowing transmission of 6 bit per symbol (time-slot), in comparison to traditional modulation formats such as OOK.

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reduced propagation delays between transverse modes

Figure 3: Graded-index few-mode fiber
Reference of source: Sumitomo Electric

By designing the refractive index profile of each core following a gradient shape, signals propagating in different modes will propagate with equal delay, hence arriving at the same time instance at the receiver.

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