In fiberoptics, a reconfigurable optical add-drop multiplexer (ROADM) is a form of optical add-drop multiplexer

Optical add-drop multiplexer

An optical add-drop multiplexer is a device used in wavelength-division multiplexing systems for multiplexing and routing different channels of light into or out of a single mode fiber . This is a type of optical node, which is generally used for the construction of optical telecommunications...

 that adds the ability to remotely switch traffic from a WDM

Wavelength-division multiplexing

In fiber-optic communications, wavelength-division multiplexing is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths of laser light...

 system at the wavelength

Wavelength

In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...

 layer. This is achieved through the use of a Wavelength selective switching

Wavelength selective switching

Wavelength Selective Switching components are industrial packages integrating devices for wavelength multiplexing/demultiplexing of WDM signals and mechanisms to switch signals on a per-wavelength basis....

 module. This allows individual or multiple wavelengths carrying data channels to be added and/or dropped from a transport fiber

Optical fiber

An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...

 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 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-based services.

The switching or reconfiguration functions of a ROADM can be achieved using a variety of switching technologies including MEMS

Microelectromechanical systems

Microelectromechanical systems is the technology of very small mechanical devices driven by electricity; it merges at the nano-scale into nanoelectromechanical systems and nanotechnology...

, Liquid crystal

Liquid crystal

Liquid crystals are a state of matter that have properties between those of a conventional liquid and those of a solid crystal. For instance, an LC may flow like a liquid, but its molecules may be oriented in a crystal-like way. There are many different types of LC phases, which can be...

, thermo optic and beam-steering switches in planar waveguide

Waveguide

A waveguide is a structure which guides waves, such as electromagnetic waves or sound waves. There are different types of waveguides for each type of wave...

 circuits, and tunable optical filter technology.