NTT is using a multi-core structure in which 12 cores are densely arranged in the amplification optical fiber, and is the world’s first company in the world to expand transmission capacity and save energy by simultaneously amplifying multiple cores in the C band (near the wavelength of 1550 nm), which is the main communication wavelength band. They achieved both This result demonstrated for the first time in the world that power consumption can be reduced by 67% compared to conventional technology, and demonstrated the possibility of adding value in power saving to transmission capacity expansion technology using multi-core fibers (MCF).
Based on the results of this demonstration, they aim to establish the technology in 2030 as a candidate for a space division multiplexing transmission line with more than 10 channels, which is the goal of the IOWN initiative.
As the capacity of transmission lines increases using space division multiplexing technology such as multi-core fibers, existing amplification technology increases the number of optical amplifiers, which increases the power consumption of the entire transmission system. On the other hand, when optical amplification technology using a multi-core structure is applied, the pumping light for amplification can be shared by multiple cores, so power savings can be achieved compared to the existing optical amplification technology using a single-core structure. 
The optical amplifier used in this research uses a cladding pumping technique, which injects pumping light into the entire cross-section of an optical fiber and amplifies all the signal light propagating through multiple cores within the cross-section all at once.