optical add/drop multiplexer (OTH) (OADM)
Optical Add/Drop Multiplexers (OADM) are optical distribution and switching components in optical networks. The OADM is a variant of a demultiplexer that filters out a limited number of wavelengths from the multiplexed signal using a Bragg grating or thin film filter.
Functionally, an otic add/drop multiplexer can add (add) or remove (drop) individual wavelengths to or from an optical fiber. The filtered-out signals can then be fed into an access network or other network, converted to a higher bit rate, or transmitted directly to a subscriber node. In this way, the optical add/drop multiplexer fulfills the functionality of an optical router, which enables transparent wavelength switching in the optical network layer.
A distinction is made between static, dynamic and reconfigurable OADMs. Static OADMs have a fixed configuration, while dynamic OADMs are remotely configurable and can add and drop connections, and reconfigurable optical add/drop multiplexers(ROADMs) have a selective element that allows them to drop individual wavelengths from the data stream.
In the physical topology of a meshed ring structure, each OADM node has its own wavelength for communicating with every other node in the ring.
Optical add/drop multiplexers come in diverse varieties. They can operate with wavelength blockers( WB) like Blocker Based OADMs( BOADM), be configurable like a Configurable OADM (COADM), be equipped with filtering techniques like the Filter Based OADM( FOADM), be reconfigurable like the Reconfigurable OADM ( ROADM), and be tunable like the Tunable OADM ( TOADM). Each of the aforementioned OADMs performs its specific task in an optical network. For example, FOADMs are best suited for static networks, while BOADMs with Wavelength Blocker (WB) are suitable for Long Haul Networks, ROADMs for 3rd and 4th degree nodes and TOADMs for Edge Networks.