Hello, everyone!
This time, I'd like to share the comparison between Fixed Grid and Flexible Grid.
Fixed Grid
The traditional 40- or 80-wavelength DWDM system uses the Fixed Grid (fixed spectrum) mode, which features a fixed center frequency and fixed wavelength spacing of 50 GHz or 100 GHz.
However, in the Fixed Grid mode, bandwidths cannot be adjusted flexibly.
With the system signal rate increase, the spectrum of optical signals is broadened. If signals of multiple rates are transmitted on a network, the maximum spectral bandwidth required by these signal rates is selected as the fixed frequency spacing, greatly wasting spectrums.
Flexible Grid
As the network traffic increases sharply, the transmission rate increases to 400 Gbit/s or even 1 Tbit/s, broadening the spectrum of optical signals.
To implement flexible spectrum allocation and improve spectrum usage, the Flexible Grid technology is utilized.
The Flexible Grid technology can provide 37.5 GHz to 400 GHz wavelength spacing.
It divides spectrums into slices with smaller widths, such as 6.25 GHz slices or 12.5 GHz slices. A high-speed signal can occupy multiple spectrum slices, implementing flexible bandwidth adjustment and improving network-wide spectrum usage.
Advantages of Flexible Grid
Spectrum slices can be selected for signals randomly so that the signals can occupy different bandwidths, and the center frequency of wavelengths can be flexibly adjusted.
Transmission of multi-rate signals on a network reduces the spacing between bands, improves bandwidth usage, and satisfies requirements for large-capacity bandwidths.
Example
When dual-carrier 400 Gbit/s signals are transmitted using the 16QAM code pattern, each 200G wavelength requires a 37.5 GHz bandwidth.
If the 50 GHz Fixed Grid mode is used, a spectral width of 100 GHz (50 GHz x 2) will be occupied.
If the Flexible Grid technology with 12.5 GHz slices is used, a spectral width of only 75 GHz (12.5 GHz x 6) will be occupied, reducing a 25 GHz bandwidth and improving spectrum usage.
VS 
That's all, thank you!
