2026.07.03
As part of the "Research and Development Project of Advanced Optical Transmission Technology Contributing to a Green Society (JPMI00316)" commissioned by the Ministry of Internal Affairs and Communications, a research group consisting of the University of Electro-Communications, Lightera Japan Co., Ltd., and Keio University, has developed a wavelength-multiplexing PON system using a hollow-core fiber developed by the Lightera Group, and has succeeded in transmitting high-power optical signals with an optical fiber input power exceeding 10W.
It is known that hollow-core fibers exhibit nonlinear effect of about 1/1000 compared to conventional silica core optical fibers, but this is the world's first time to achieve high-quality, high-power transmission using actual communication optical signals exceeding 10W.
In wireless systems represented by fifth-generation mobile communication systems (5G), with the increasing frequency of wireless signals, numerous wireless base stations for mobile communications and IoT (Internet of Things) have been required.
Therefore, applying PON systems, which are currently used for subscriber-based optical networks, is being considered. By combining wavelength division multiplexing, even larger capacity communications are expected.
Furthermore, by utilizing optical fiber lines, there is growing anticipation for realizing optical fiber power supply aiming at ensuring the availability of wireless base stations during disasters and reducing the need for conventional power supply.
In downlink transmission of PON systems, increasing the power of optical signals for communication enables communication to more wireless base stations. However, in silica core optical fibers, which are currently the most widely used, nonlinear effects occur in the core and greatly limit the optical signal power for communication.
If the optical power that can be transmitted by optical fiber can be dramatically improved, it will be possible to transmit not only signals for communication but also light energy, and to supply power to wireless base stations, thereby improving their availability during disasters.
In this study, we newly introduced hollow-core fiber between the OLT and splitter of the PON system, and by multiplexing four wavelengths of optical signals modulated by the 5G NR signal at a carrier frequency of 28 GHz, which is the 5G standard, we have successfully greatly suppressed various types of nonlinear effects, which are easily generated in conventional silica core optical fibers, and achieved high-quality, high-power transmission exceeding 10W.
This indicates that more than 4,096 branches would be possible for PON systems where the optical transmissions are shared by many subscribers.
In this experiment, four wavelengths were used for communication. We plan to build a PON system for mobile communication and IoT that enables communication with more wireless base stations by multiplexing more wavelengths over a wider wavelength range.
The content developed this time is scheduled to be published in the August 2026 issue of the Journal of Optical Communications and Networking, published by IEEE and Optica Publishing Group.
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