Fujitsu and KDDI develop large-capacity optical fiber transmission tech

Fujitsu Limited and KDDI Research today announced that they have successfully developed a large-capacity multiband wavelength multiplexing transmission technology using installed optical fibers.

The two companies have developed a technology that enables transmission of wavelength bands other than the C band, which has not been used in medium- and long-distance commercial optical communications, using a batch wavelength conversion and multiband amplification technology. The optical fiber communications network introduced with this technology enables wavelength transmission at 5.2 times the wavelength multiplicity of current commercial optical transmission technology. This enables the use of installed optical fiber facilities to increase communication traffic in a cost-effective and labor-efficient manner. The technology makes it easier to expand the transmission capacity in urban areas and densely populated residential areas where installation can prove challenging, and offers the potential to significantly reduce the time required to start the service and reduce costs.

The development was undertaken as part of the ”Research and Development Project of the Enhanced Infrastructures for Post-5G Information and Communication Systems” commissioned by Japan’s New Energy and Industrial Technology Development Organization (NEDO).

Project background
Amidst growing demand for services that leverage IoT, artificial intelligence (AI), and big data analysis, NEDO aims to strengthen the development and manufacturing base of Japan’s post-5G information and communications systems by developing core technologies for post-5G information and communications systems. As part of this effort, from October 2020 to October 2023, Fujitsu and KDDI Research engaged in a project to enhance the performance of post-5G optical networks. Conventional commercial optical fiber communication networks use single-mode fibers in which light passes only through the center of the optical fiber, and use the C band (wavelength band: 1,530 nm to 1,565 nm) (3) as the signal transmission band of the optical network. However, as the amount of communication traffic increases, the C band alone is expected to have insufficient transmission capacity. To increase the transmission capacity per fiber, the two companies aimed to increase the wavelength band used from the C band to the L band (1,565 nm to 1,625 nm), the S band (1,460 nm to 1,530 nm), the U band (1,625 nm to 1,675 nm), and the O band (1,260 nm to 1,360 nm), with the aim of making it multi-band.

Project results
As part of the project, Fujitsu built a simulation model that accounts for the degradation factors of transmission performance in multiband transmission, enabling the transmission design of multiband wavelength multiplexing systems. The simulation model reflects the measurement results of the commercial optical fiber characteristics and the transmission parameters extracted by the experimental system verification of the integrated wavelength converter/multiband amplifier. Using this model, Fujitsu realized high-precision simulations that reduce errors from the actual measurement to within 1dB, making it possible to take into account the interaction between bands and the degradation of transmission performance.
KDDI Research’s research has made it possible to utilize twice the frequency bandwidth of the conventional C band in the O band, which has never been utilized in high-density wavelength division multiplexing (DWDM transmission. Combining both technologies, the two companies conducted actual transmission experiments using existing optical fibers and demonstrated multiband wavelength multiplexed transmission (transmission distance 45 km) in the O, S, C, L, and U bands, proving that wavelength transmission is possible at 5.2 times the wavelength multiplicity of conventional C-band-only transmission. The two companies also confirmed multi-band wavelength multiplexing transmission (transmission distance 560 km) in the S, C, L and U bands in the simulation.

In the conventional design of a transmission system in the C band, parameters that could be treated as constants would not have practical problems, but in the case of multiband transmission over the S band + C band + L band + U band, the difference in transmission performance between the wavelength bands cannot be ignored, and a design that takes into account the wavelength dependence is required. For example, nonlinear degradation factors become more pronounced as the optical power input to the transmission line increases and as the transmission distance increases, thereby limiting transmission performance. In particular, stimulated Raman scattering, cross-phase modulation, and four-wave mixing caused by the interaction of light with multiple wavelengths are prominent at high wavelength multiplicities, which greatly affect the transmission performance of multiband wavelength multiplexing systems.

In this project, Fujitsu and KDDI Research established a design method for multi-band wavelength multiplexing systems by constructing a simulation model that takes into account the interaction between different bands and degradation factors in transmission performance. In addition, since wavelength division multiplexing (WDM) optical signals in the S and U bands are generated by all-optical signal processing technology from optical signals in the C and L bands, respectively, there is no need to use transmitters and receivers dedicated to the S and U bands. The integration of these technologies has enabled DWDM transmission in the S band + C band + L band + U band using coherent transmission technology, which leverages the phase of light, thus enabling high-speed and high-capacity communication.

CT Bureau