View source for Reconfigurable optical add-drop multiplexer

{{Short description|Optical network component}}

In [[optical communication]], a '''reconfigurable optical add-drop multiplexer''' ('''ROADM''') is a form of [[optical add-drop multiplexer]] that adds the ability to remotely switch traffic from a [[wavelength-division multiplexing]] (WDM) system at the [[wavelength]] layer. This is achieved through the use of a [[wavelength selective switching]] module. This allows individual or multiple wavelengths carrying data channels to be added and/or dropped from a transport [[optical fiber|fiber]] without the need to convert the signals on all of the WDM channels to electronic signals and back again to optical signals.

The main advantages of the ROADM are:
* The planning of entire bandwidth assignment need not be carried out during initial deployment of a system. The configuration can be done as and when required without affecting traffic already passing the ROADM.
* ROADM allows for remote configuration and reconfiguration.
* In ROADM, as it is not clear beforehand where a signal can be potentially routed, there is a necessity of power balancing of these signals. ROADMs allow for automatic power balancing.

ROADM functionality originally appeared in long-haul [[Wavelength-division multiplexing#Dense WDM|dense wavelength division multiplexing]] (DWDM) equipment, but by 2005, it began to appear in metro optical systems because of the need to build out major metropolitan networks in order to deal with the traffic driven by the increasing demand for [[packet (information technology)|packet]]-based services.

The switching or reconfiguration functions of a ROADM can be achieved using a variety of switching technologies including [[microelectromechanical systems]] (MEMS), [[liquid crystal]], [[thermo optic switch|thermo optic]] and beam-steering switches in planar [[waveguide]] circuits, and tunable [[optical filter]] technology. MEMS and liquid crystal technologies are the most widely used.{{when|date=October 2024}} ROADMs were first introduced in 2002 with the introduction of DWDM.<ref>{{cite web | url=https://www.fibre-systems.com/feature/roadm-ahead | title=The ROADM ahead &#124; Fibre Systems }}</ref> ROADMs can be directionless, colorless, contentionless, and gridless. Directionless means that any wavelength can be dropped from any fiber, and any wavelength or signal can be sent to any port in the ROADM. Colorless implies every port in the ROADM can handle or accept any wavelength or color of light. Contentionless means several identical wavelengths or signals can be dropped from several ports at the same time. Gridless means that the ROADM can handle frequencies or signals that aren't precisely 50&nbsp;GHz apart from each other. This is relevant because 50&nbsp;GHz spacing has been traditionally used in fiber optic communications.<ref>{{cite book | url=https://books.google.com/books?id=SlclBAAAQBAJ&dq=directionless+roadm&pg=PA176 | isbn=978-3-319-05227-4 | title=Optical Network Design and Planning | date=6 May 2014 | publisher=Springer }}</ref><ref>{{cite book | url=https://books.google.com/books?id=EisDEAAAQBAJ&dq=directionless+roadm&pg=PA620 | isbn=978-3-030-16250-4 | title=Springer Handbook of Optical Networks | date=15 October 2020 | publisher=Springer }}</ref><ref>{{cite book | url=https://books.google.com/books?id=-VJ2DAAAQBAJ&dq=directionless+roadm&pg=SA5-PA17 | isbn=978-0-12-806818-2 | title=Handbook of Fiber Optic Data Communication: Chapter 5. Optical Wavelength-Division Multiplexing for Data Communication Networks | date=9 August 2013 | publisher=Elsevier Inc. Chapters }}</ref><ref>{{cite book | url=https://books.google.com/books?id=SlclBAAAQBAJ&dq=roadm+gridless&pg=PA423 | isbn=978-3-319-05227-4 | title=Optical Network Design and Planning | date=6 May 2014 | publisher=Springer }}</ref>

== See also ==
* [[Optical mesh network]]

== References ==
{{reflist}}
{{refbegin}}
* [http://img.lightreading.com/heavyreading/pdf/hr20050517_esum.pdf Light Reading's Heavy Reading - "ROADMs and the Future of Metro Optical Networks", May 2005]
* [http://www.seefire.org/content/modules/downloads/SEEFIRE-WP2-Deliverable2.1-p-20051115x.pdf South-East Europe Fibre Infrastructure for Research and Education - Dark Fibre Lighting Technologies]
{{refend}}

[[Category:Telecommunications equipment]]
[[Category:Networking hardware]]