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A further consideration that had to be addressed enabled DWDM transmission in the combined
was the fact that whilst in the conventional design S,C,L and U bands using coherent transmission
of a transmission system parameters that could technology to be achieved, leveraging the phase
be treated as constants would not have practical of light to enable high-speed and high capacity
consequences, multiband transmission over the communication.
combined S,C,L and U bands could not ignore the
Finally, coherent transmission technology tends
difference in transmission performance between the
to distort O-band transmission signals due to the
wavelength bands, necessitating a design that that
influence of other optical components with nonlinear
takes into account the the wavelength dependence.
noise often arising in the O-band, which can be
For example, nonlinear degradation factors
difficult to eliminate with digital signal processing.
become more pronounced as the optical power
Minimisation of nonlinear noise, however, can be
input to the transmission line increases and as the
achieved by appropriate setting of the transmitted
transmission distance increases, thereby limiting
optical power for each densely multiplexed
transmission performance. In particular, stimulated
wavelength signal, achieving coherent DWDM
Raman scattering, cross-phase modulation and
transmission over 9.6THz even when the process
four-wave mixing caused by the interaction of
of signal compensation on the transmitter side
light with multiple wavelengths are prominent at
and wavelength dispersion compensation on the
high wavelength multiplicities, greatly affecting the
receiver side are omitted.
transmission performance of multiband wavelength
multiplexing systems. Major advantages associated with the O-band are
notably that it is a wavelength band with near-zero
A simulation model was therefore constructed that
dispersion, is less affected by wavelength dispersion,
takes into account the interaction between different
and reduces the load on digital signal processing.
bands and degradation factors on transmission
performance. Also, since wavelength division [ Reference: Fowle, H., ‘Fujitsu and KDDI Research
multiplexing optical signals in the S and U bands Large Capacity Multiband Wavelength Multiplexing
are generated by all-optical signal processing Transmission’, Electronic Specifier, 4th. December
technology from optical signals in the C and L bands 2023 ]
respectively, the need for transmitters and receivers
dedicated to the S and U bands was removed.
The integration of these technologies has thus

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