What is FOADM and ROADM

What is FOADM and ROADM

What is OADM

First of all, OADM is a device used in WDM networks. In this device, the main function is to couple two or more wavelengths into the same optical fiber to increase the total bandwidth between two points. In a traditional WDM network, the optical layer demultiplexer usually has an OMU optical multiplexer, an ODU optical demultiplexer, and an OADM optical demultiplexer in the middle. Among them, OADM is divided into FOADM (Fix Optical Add-Drop Multiplex) and ROADM (Reconfigurable Optical Add-Drop Multiplexer).

What is FOADM

FOADM (Fixed Optical Add/Drop Multiplexer), as the name suggests, means that the number of wavelengths is fixed and the optical direction is fixed. Which wavelength channel is added or dropped? The answer is no choice. Fixed optical add/drop multiplexers can only add and drop channels with specified wavelengths, and cannot dynamically adjust settings to add and drop other channels.

In the FOADM structure here, it is possible that an OADM single board contains the function of splitting and multiplexing, for example, a 4/8 on-road add-drop multiplexing single board. It may also be two sets of OMU/ODU, back to back to form FOADM. In fact, this is just a name, understand it, and there is not much difference. For example, you can simply understand that two OTMs back to back form a FOADM (OADM).

What is ROADM

ROADM (Reconfigurable Optical Add-Drop Multiplexer) is a device used in a dense wavelength division multiplexing (DWDM) system. Its function is to dynamically add or drop service wavelengths through remote reconfiguration. That is to say, in the middle of the line, the wavelength of the upper and lower services can be arbitrarily assigned as needed to achieve flexible scheduling of services. In ROADM, we use WSS (Optical Wavelength Selective Switch) to add and insert any single-wave or multiplexed signal from the multiplexed signal to achieve dynamic optical wavelength scheduling in multiple dimensions. And the reverse process of the above process can be realized.

The internal structure of WSS is as follows:

After the network node adopts ROADM, the network management system can control a certain wavelength to pass through this optical node or drop from the local port. There is no need to go to the station to jump fibers like FOADM, so that quick service assignment, more automated processing, simplified network planning and construction, making it more powerful than traditional wavelength division (OTM/FOADM) network monitoring ability and network expansion capabilities.