Functions and Applications of Optical Add-drop Multiplexer (OADM)

What does optical add-drop multiplexer stand for
Functions of OADM
Applications of OADM

1,What does optical add-drop multiplexer stand for
OADM is Optical Add-Drop Multiplexer, which used in WDM systems for multiplexing and routing different channels of light into or out of a single mode fiber. Its main function is to selectively drop or add one or multiple wavelength channels without affecting the transmission of other wavelength channels. The OADM device is one of the key devices of the all-optical network.

“Add” refers to the capability of the device to add one or more new wavelength channels to an existing multi-wavelength WDM signal while “drop” refers to drop or remove one or more channels, passing those signals to another network path.

2,Functions of OADM
A traditional OADM consists of multiplexer, demultiplexer and between them a method of reconfiguring the paths between the Mux, Demux and a set of ports for adding and dropping signals.

The add and drop units achieve the core functions of OADM, removes or drops a wavelength from a multiplicity of wavelengths in a fiber and separating the signals from the particular channel. Demultiplexers drop the signal of the optical trunk. And then adds the same wavelength in the same direction of data flow, but with different data content. Multiplexers are used to couple two or more wavelengths into the same fiber.

3,Types of OADM (FOADM, TOADM)
There are two main types of OADM that are widely used in communication networks: Fixed OADM (FOADM) and Reconfigurable OADM (ROADM).

FOADM can only add and drop bands with specified wavelengths. FOADMs have pre-assigned channels at static nodes and allowed adding and dropping of individual or multiple wavelength channels from a DWDM.

The figure shows simple schematic diagram of FOADM. Firstly, demux separates all wavelengths, drops the specified wavelengths to the local nodes, and pass the rest of the wavelengths through the node. Another local specified wavelength is added, together with other wavelengths driven through Mux to next node. Here is the problem, you can’t temporarily change the add/drop wavelengths because it’s all fixed.

The common FOADM can be divided into three types, thin film filter type (TFF type), fiber Bragg grating (FBG type) and integrated planar arrayed waveguide grating (AWG type). From the frequency band, FOADM can be divided into DWDM OADM and CWDM OADM.

ROADM is a component used in DWDM systems. It can dynamically add and drop wavelengths through remote reconfiguration, which can realize the flexible configuration of the businesses according to the needs. WSS (Wavelength Selective Switch) is usually selected to add/drop arbitrary single-wave or multiplex-waves. Unlike fixed optical add-drop multiplexers ROADMs allow you online reconfiguration without affecting traffic.

In order to realize non-blocking switching and adding/dropping of wavelengths, the new generation of ROADM nodes are required to be colorless, directionless and contentionless (CDC ROADM). The revolutionary advantage of CDC-ROADM is that it can upload and download any band on any port, and at the same time solve the problem that the same band cannot be placed on the same path, which greatly reduces the difficulty of fault recovery efficiency. A ROADM node is usually constructed with wavelength selective switches (WSSs) and other modules. The CDC functions depends on the configuration of the ROADM node, while the flexgrid function depends on the key module WSS. Unlike fixed OADMs, ROADMs allow online reconfiguration without affecting traffic.

Based on cost consideration, the current metro network is mainly based on CWDM and FOADM (fixed optical add/drop multiplexer) technologies. The DWDM and ROADM technologies for long haul network are expected to sink to metro network.

4,Applications of OADM
MAN (Metropolitan Area Network)
OADM has a business in the middle of choice. Of course, the main battlefield of application is MAN (metropolitan area network). That can be working flexibility, easy to upgrade and amplify the network. An Ideal multi-services transport platform in MAN application.

OXC (Optical Cross Connection)
OADM allows different optical network of different wavelength multiplexing signal at different locations.


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