- 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.
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.
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.
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.
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.