In Fiber optic communication networks Add-Drop multiplexer drops and/or adds one or more optical channels to a signal. This device is an important element of an optical fiber network.
A multiplexer combines several lower-bandwidth streams of data into a single beam of light. An add-drop multiplexer also does the same function of adding one or more lower-bandwidth signals to an existing high-bandwidth data stream. At the same time, an add-drop multiplexer can extract or takeout other low-bandwidth signals, removing them from the stream and redirecting them to some other network path. This is used as a local “on-ramp” and “off-ramp” to the high-speed fiber optic network.
Add/drop multiplexers are manufactured using gratings burned into the core of an optical fiber using masks and UV light, a splitter/coupler having two types of wavelength-specific fibers twisted into them or on a planar waveguide grating manufactured on photonic bandgap type materials.
Add-Drop-Multiplexers are used in long-haul fiber optic networks and also in short-distance networks such as Metro, Metro-core etc. Use of Add-drop multiplexers in long distance communication is expensive due to the difficulty of scaling the technology to the high data rates and the use of DWDM technology in long distance communications.
The predominant optical filtering technology employed in add-drop multiplexers is the Fabry–Perot etalon.
MSPP (Multi-Service Provisioning Platform), a relatively new comer in the technology, which is also called Multi-Service SONET/SDH has the functions and capabilities of a legacy Add-Drop Multiplexer. Additionally, MSPP can include Cross-Connect function to enable management of multiple fiber rings in a single chasis. MSPP can be connected directly to the Ethernet LANs to a service provider’s optical backbone and is now slowly replacing the market of ADMs.
New designs are emerging in ADM market. As more telecom operators starts investment in Metro fiber optic networks, a new form of ADM has been developed, which is Reconfigurable Optical Add-Drop Multiplexer or ROADM.