An optical add-drop multiplexer (OADM) is a device used in wavelength-division multiplexing systems for multiplexing and

routing Routing is the process of selecting a path for traffic in a network or between or across multiple networks. Broadly, routing is performed in many types of networks, including circuit-switched networks, such as the public switched telephone netw ...

different channels of

light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 tera ...

into or out of a

single mode fiber In fiber-optic communication, a single-mode optical fiber (SMF), also known as fundamental- or mono-mode, is an optical fiber designed to carry only a single mode (electromagnetism), mode of light - the transverse mode. Modes are the possible s ...

(SMF). This is a type of optical node, which is generally used for the formation and the construction of optical telecommunications networks. "Add" and "drop" here refer to the capability of the device to add one or more new wavelength channels to an existing multi-wavelength WDM signal, and/or to drop (remove) one or more channels, passing those signals to another network path. An OADM may be considered to be a specific type of

optical cross-connect {{unreferenced, date=February 2008 An optical cross-connect (OXC) is a device used by telecommunications carriers to switch high-speed optical signals in a fiber optic network, such as an optical mesh network. There are several ways to realize a ...

. A traditional OADM consists of three stages: an optical

demultiplexer In electronics, a multiplexer (or mux; spelled sometimes as multiplexor), also known as a data selector, is a device that selects between several analog or digital input signals and forwards the selected input to a single output line. The sel ...

, an optical

multiplexer In electronics, a multiplexer (or mux; spelled sometimes as multiplexor), also known as a data selector, is a device that selects between several analog or digital input signals and forwards the selected input to a single output line. The sel ...

, and between them a method of reconfiguring the paths between the demultiplexer, the multiplexer and a set of ports for adding and dropping signals. The demultiplexer separates

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

s in an input fiber onto ports. The reconfiguration can be achieved by a fiber patch panel or by

optical switch An optical transistor, also known as an optical switch or a light valve, is a device that switches or amplifies optical signals. Light occurring on an optical transistor's input changes the intensity of light emitted from the transistor's output ...

es which direct the wavelengths to the multiplexer or to drop ports. The multiplexer multiplexes the wavelength channels that are to continue on from demultiplexer ports with those from the add ports, onto a single output fiber. OADM module

All the lightpaths that directly pass an OADM are termed ''cut-through lightpaths'', while those that are added or dropped at the OADM node are termed ''added/dropped lightpaths''. An OADM with remotely reconfigurable optical switches (for example 1×2) in the middle stage is called a reconfigurable OADM (ROADM). Ones without this feature are known as ''fixed'' OADMs. While the term OADM applies to both types, it is often used interchangeably with ROADM. Physically, there are several ways to make an OADM. There are a variety of demultiplexer and multiplexer technologies including thin film filters, fiber Bragg gratings with

optical circulator An optical circulator is a three- or four-port optical device designed such that light entering any port exits from the next. This means that if light enters port 1 it is emitted from port 2, but if some of the emitted light is reflected back to t ...

s, free space grating devices and integrated planar

arrayed waveguide grating {{Unreferenced, date=April 2019 Arrayed waveguide gratings (AWG) are commonly used as Optical add-drop multiplexer, optical (de)multiplexers in wavelength division multiplexing, wavelength division multiplexed (WDM) systems. These devices are capa ...

s. The switching or reconfiguration functions range from the manual fiber patch panel to a variety of switching technologies including microelectromechanical systems (MEMS), liquid crystal and thermo-optic switches in planar

waveguide A waveguide is a structure that guides waves, such as electromagnetic waves or sound, with minimal loss of energy by restricting the transmission of energy to one direction. Without the physical constraint of a waveguide, wave intensities de ...

circuits. Although both have add/drop functionality, OADMs are distinct from

add-drop multiplexer An add-drop multiplexer (ADM) is an important element of an optical fiber network. A multiplexer combines, or multiplexes, several lower-bandwidth streams of data into a single beam of light. An ''add-drop'' multiplexer also has the capabili ...

s. The former function in the photonic domain under wavelength-division multiplexing, while the latter are implicitly considered to function in the traditional

SONET/SDH Synchronous optical networking (SONET) and synchronous digital hierarchy (SDH) are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting diod ...

networks.

References

* {{refend

Add-drop multiplexer An add-drop multiplexer (ADM) is an important element of an optical fiber network. A multiplexer combines, or multiplexes, several lower-bandwidth streams of data into a single beam of light. An ''add-drop'' multiplexer also has the capabili ...

Multiplexing

See also

References