29. November 2021


ITU-Grid: Channel spacing for DWDM multiplexing

Over and over again, in connection with optical transmission systems, people ask how ITU-Grid or the ITU channel can be used to increase the capacity of the signals to be transmitted and how this technology works. This involves first of all understanding what Wavelength Division Multiplexing (WDM) does.

How does WDM work?

WDM is a technology that makes it possible to provide higher data throughput with multiple services over an existing fiber optic infrastructure. The technology combines multiple wavelengths – corresponding frequencies – on a single optical fiber. This enables several data channels to be operated independently of each other on one optical fiber by using different wavelengths. This process is also known as optical multiplexing or wavelength division multiplexing.

What does ITU mean?

The International Telecommunication Union (ITU), headquartered in Geneva, is a specialized agency of the United Nations that not only deals with technical aspects of telecommunications in general, but also defines standards or issues recommendations that can be found in the area of wavelength division multiplexing, among other things.

As a result ITU has defined wavelengths and channel spacing for wavelength division multiplexing (WDM), coarse wavelength division multiplexing (CWDM) and dense wavelength division multiplexing (DWDM). Depending on the technology used, the wavelengths as well as the channel spacing between the wavelengths differ.

The standard DWDM range of the ITU Grid covers 1520.25 nm to 1577.03 nm and is mainly located in the C-band. For interference-free operation of optical multiplexing, channel spacing must be strictly observed. These can have a spacing of 100 GHz (0.8 nm), 75 GHz (0.6 nm) or 50 GHz (0.4 nm).

Overview of the frequency bands

Higher ranges and better signal quality are achieved through the specific selection of wavelengths. They are distinguished by the following optical bands:

  • Extended E-band 1360-1460 nm
  • Short wavelength S-band 1460-1530 nm
  • Conventional C-band 1530-1565 nm
  • Long wavelength L-band 1565-1625 nm
  • Ultra-long-wavelength U-band 1625-1675 nm