Carrying on from muxponding last Friday, we continue our weekly series on Dark Fibre. In the previous post, we saw how lower rate signals are combined into a larger rate signal. We are continuing that theme as we look at multiplexing optical signals in DWDM systems with a look at wavelength division multiplexing (WDM), the parent technology of DWDM.

Fibre optics transports data using optical technology though the amount of data that can travel along a fibre optic cable, dark or lit, is limited. WDM resolves this obstacle by transmitting multiple wavelengths or channels where channel is filled by an optical signal. Here we can visualise this concept.

Wavelength Division Multiplexing

Each transponder will transmit a different wavelength of light and the number of wavelengths per fibre pair are subject to spectral width and spacing between wavelengths. Two setup examples of 100GHz spacing and 50GHz between wavelengths typically have 40 and 88 channels respectively with the 100G solution from Sorrento Networks providing a total of 8.8 Tbps (Terabits per second).

Such wavelengths are organised using a frequency grid that is defined by ITU-T G.694.1. By any means, applications are not limited to this with flexible grids a potential measure as well. We’ll learn more about flexible and fixed grids later on in this series.

We can therefore see how WDM of which DWDM is a sub-technology can fundamentally increase bandwidth on dark fibre networks with a scalable and cost-effective solution. In next week’s post we’ll see how 100G and above sub-terabit rates on Dark Fibre, including 100G – 400G line rates are achieve.

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