What is ROADM?

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  • Written By: Malcolm Tatum
  • Edited By: Bronwyn Harris
  • Last Modified Date: 11 October 2019
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The reconfigurable optical add-drop multiplexer or ROADM is a device that is utilized on many different fiber optic networks. Essentially, this type of multiplexer has the ability to control the direction and focus of both infrared and visible light emissions within a range of different wavelengths. The technology of ROADM makes it unnecessary to convert these emissions into electrical signals that must be converted back into their original form at the point of termination. ROADM is often utilized with any system that makes use of wavelength division multiplexing or WDM.

The basics of ROADM are relatively straightforward. Three operations take place within the operating process of this type of optical add-drop multiplexer. These functions are known as add, drop, and cut-through. The visible or infrared light outgoing signal that is generated constitutes the add function on the multiplexer. At the same time, the ability to terminate the reception of an incoming infrared or visible light emission is known as the drop. The cut-through takes place when the beam passes through the multiplexer without any type of modification taking place.

Currently, there are two similar technologies for ROADM that are in common use. Wavelength blocking technology is the older version of ROADM that involves initiating a wavelength chance in the signal in order to accommodate a given channel. This is accomplished by filtering the light emission and extracting the data for inclusion in a different emission on a different wavelength.


Planar light-wave circuit is the second common form of ROADM. With PLC, the conversion process found in wavelength blocking technology is still present, but is streamlined. This means less time to process the light signal, less ancillary equipment required to interact with the transport fiber, and thus a lower cost for the operation.

However, it should be noted that neither approach to ROADM functionality constitutes an actual process of optical branching, in that it is not possible to direct a given beam of light to a specific port without engaging in several key intermediate steps. However, there is research currently underway to refine an enhanced version of ROADM that will account for this and make optical branching possible through the use of the multiplexer.


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