Fujitsu and KDDI Research have successfully developed a large-capacity multiband wavelength multiplexing transmission technology using installed optical fibres.
The new technology from the two companies enables transmission of wavelength bands other than the C band, using a batch wavelength conversion and multiband amplification technology.
Expanding transmission capacity in challenging areas
The companies say that the optical fibre communications network introduced with this technology could enable wavelength transmission at 5.2 times the wavelength multiplicity of current commercial optical transmission technology. This enables the use of installed optical fibre facilities to increase communication traffic in a cost-effective and labour-efficient manner. The technology could also make it easier to expand the transmission capacity in urban and densely populated residential areas where installation can prove challenging, and offers the potential to 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 (1) Information and Communication Systems” (2) commissioned by Japan’s New Energy and Industrial Technology Development Organization (NEDO).
Image of the system applying high-capacity multiband wavelength multiplexing transmission technology (Credit: Fujitsu)
NEDO aims to strengthen the development and manufacturing base of Japan's post-5G information and communications systems by developing core technologies for these systems. As such, 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 fibre communication networks use single-mode fibres in which light passes only through the centre of the optical fibre, and use the C band 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 fibre, the two companies aimed to increase the wavelength band used from the C band to the L band, the S band, the U band, and the O band, with the aim of making it multi-band.
The potential results for optical communications
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 fibre characteristics and the transmission parameters extracted by the experimental system verification of the integrated wavelength converter/multiband amplifier.
Using this model, Fujitsu realised 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 use twice the frequency bandwidth of the conventional C band in the O band, which has never been used in high-density wavelength division multiplexing (DWDM) transmission. Combining both technologies, the two companies conducted actual transmission experiments using existing optical fibres 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.
Received optical spectrum of a single installed fibre when the O, S, C, L, and U bands are transmitted simultaneously (Credit: Fujitsu)
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, enabling high-speed and high-capacity communication.
Transition of signal optical power between multibands by stimulated Raman scattering; above: The case without control; below: The case with control so that the optical power distribution after fibre propagation is uniform (Credit: Fujitsu)
This approach minimised the effects of nonlinear noise, so could also overcome the challenges associated with coherent transmission technology distorting O-band transmission signals. It achieves coherent DWDM transmission over 9.6 THz in the O band, even if the process of signal compensation on the transmitter side and wavelength dispersion compensation on the receiver side was omitted. The O band can be less affected by wavelength dispersion and has the advantage of reducing the load on digital signal processing and improving energy efficiency.