optical communication Optical communication, also known as optical telecommunication, is communication at a distance using light to carry information. It can be performed visually or by using electronic devices. The earliest basic forms of optical communication date ...

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

optical add-drop multiplexer An optical add-drop multiplexer (OADM) is a device used in wavelength-division multiplexing (WDM) systems for multiplexing and routing different channels of light into or out of a single-mode fiber (SMF). This is a type of optical node, which ...

that adds the ability to remotely switch traffic from a

wavelength-division multiplexing In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i.e., colors) of laser light. This techn ...

(WDM) system at the

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

layer. This is achieved through the use of a

wavelength selective switching Wavelength selective switching components are used in WDM optical communications networks to route (switch) signals between optical fibres on a per-wavelength basis. What is a WSS A WSS comprises a switching array that operates on light that ha ...

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

fiber Fiber (spelled fibre in British English; from ) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often inco ...

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 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 Packet may refer to: * A small container or pouch ** Packet (container), a small single use container ** Cigarette packet ** Sugar packet * Network packet, a formatted unit of data carried by a packet-mode computer network * Packet radio, a form ...

-based services. The switching or reconfiguration functions of a ROADM can be achieved using a variety of switching technologies including

microelectromechanical systems MEMS (micro-electromechanical systems) is the technology of microscopic devices incorporating both electronic and moving parts. MEMS are made up of components between 1 and 100 micrometres in size (i.e., 0.001 to 0.1 mm), and MEMS devices ...

(MEMS),

liquid crystal Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal can flow like a liquid, but its molecules may be oriented in a common direction as i ...

, thermo optic and beam-steering switches in planar

waveguide A waveguide is a structure that guides waves by restricting the transmission of energy to one direction. Common types of waveguides include acoustic waveguides which direct sound, optical waveguides which direct light, and radio-frequency w ...

circuits, and tunable

optical filter An optical filter is a device that selectively transmits light of different wavelengths, usually implemented as a glass plane or plastic device in the optical path, which are either dyed in the bulk or have interference coatings. The optic ...

technology. MEMS and liquid crystal technologies are the most widely used. ROADMs were first introduced in 2002 with the introduction of DWDM. 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 GHz apart from each other. This is relevant because 50 GHz spacing has been traditionally used in fiber optic communications.

References

Light Reading's Heavy Reading - "ROADMs and the Future of Metro Optical Networks", May 2005

South-East Europe Fibre Infrastructure for Research and Education - Dark Fibre Lighting Technologies
{{refend Telecommunications equipment Networking hardware

See also

References