Optical Add-Drop Multiplexer Tutorial

What is Optical Add-Drop Multiplexer (OADM)?

OADM is a device with optical signal to realize optical domain channel multiplexing. The main implementation technologies are WDM(Wavelength Division Multiplexing), O-CDMA(Optical Code Division Multiple Access) and OTDM(Optical Time Division Multiplexing). OADM is the key of AON(All-Optical Network).

Optical Add-Drop Multiplexer is used in 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 is generally used for 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, 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.

The Structure and Principle of Optical Add-Drop Multiplexer

OADM consists of MUX(multiplexer), DEMUX(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 MUX multiplexes the wavelength channels that are to continue on from DEMUX ports with those from the add ports, onto a single output fiber, while the DEMUX separates wavelengths in an input fiber onto ports. The reconfiguration can be achieved by a fiber patch panel or by optical switches which direct the wavelengths to the MUX or to drop ports.

All the light paths 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.

General OADM node can use four port model to represent, includes three basic functions: Drop required wavelength signal, Add rumored signal to other wavelengths pass through unaffected. OADM specific network process is as follows: WDM signal coming from the line contains mangy wavelength signals into OADM's "MainInput" side, according to business required, from many wavelength signals to selectively retrieved from the end (Drop) output desired wavelength signal, relative to the end from the Add the wavelength of the input signal to be transmitted. While the other has nothing to do with the local wavelength channels directly through the OADM, and rumored signals multiplexed together, the line output from the OADM (Main Output) Output.

Physically, there are several ways to realize an OADM. There are a variety of demultiplexer and multiplexer technologies including TFF(thin film filter), FBG(fiber bragg grating) with optical circulators, free space grating devices and integrated planar arrayed waveguide gratings. 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 circuits.

Array waveguide FBG can create different types of OADM structures. Also it can use all fiber optic technology to construct all-optical OADM. What should be pay attention is that no matter what kind of OADM, the basic requirement is the same, such as small loss,higher isolation degree between channel, polarization insensitive to changing temperature, tolerant signal source drift and jitter within a certain range. Also in the process to be able to guarantee basic consistent between the various channels of the transmission of power. Last, strive to keep simple and convenient that can achieve high performance ratio.

Tips: Although both have add/drop functionality, OADMs are distinct from add-drop multiplexers. The former function in the photonic domain under wavelength-division multiplexing, while the latter are implicitly considered to function in the traditional SONET/SDH networks.

The Main Functions and Applications of the OADM

Functions

OADM can be separated from the multiple wavelength channels or insert one or more wavelengths. There are fixed type and configuration type. Fixed type only have one or more fixed wavelength, the node's routing is determined. However, fixed type is not flexibility, but in reliable performance and time saving. It can be reconfigurated the node channel wavelength of OADM, allocates the wavelength of network resources properly.


Applications


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

2. OXC(Optical Cross Connection)
OADM allows different optical network of different wavelength multiplexing signal at different locations. Propsed equipment allow different network connect dynamic. On-demand wavelength resources, a wider range of network interconnection. OADM and OXC only need to download the information in the nodes to send a person to handle the equipment, including ATM switchboard, SDH switchboard, IP router etc., which greatly improve the efficiency of the node to process information.

The Types and Solutions of Optical Add-Drop Multiplexers

According to the multiplexing wavelengths, OADMs can be divided into two types which are CWDM OADM and DWDM OADM.


CWDM OADM

CWDM OADM is designed for the CWDM passive optical systems. It can multiplex/demultiplex or add/drop wavelengths from multiple fibers onto one optical fiber. Here takes the Cisco CWDM OADMs for an example.

The OADM connectors are interfaced to the color-matching CWDM GBIC modules on the equipment side. All the transceiver modules have the same size. The Cisco CWDM 2-slot chassis allows you to rack mount up to two CWDM OADMs in a single rack unit. There are four different types of CWDM OADMs.

1. Dual Single-Channel OADM
Dual single-channel OADM allows you to add/drop two channels of the same wavelength into the two directions of an optical ring. The other wavelengths are passed through the OADM. Dual fiber is used for both the network and the CWDM GBIC connections. Eight versions of this OADM are available, one for each wavelength of light. The dual single-channel OADMs are color coded and match the color coding of the CWDM.

2. 4-Channel OADM
4-Channel OADM (CWDM-MUX-4=) allows you to add/drop four channels (with different wavelengths) into one direction of an optical ring. The other wavelengths are passed through the OADM. Dual fiber is used for both the network and the GBIC connections. The four wavelengths are set to 1470 nm, 1510 nm, 1550 nm, and 1590 nm.

3. 8-Channel MUX/DEMUX
8-Channel CWDM MUX/DEMUX (CWDM-MUX-8=) allows you to multiplex/demultiplex eight separate channels into one pair of fiber. Dual fiber is used for both the network and the GBIC connections. The eight available wavelengths are 1470 nm, 1490 nm, 1510 nm, 15300 nm, 1550 nm, 1570 nm, 1590 nm, and 1610 nm.

4. Single Fiber 4-Channel MUX/DEMUX
Single fiber 4-channel CWDM MUX/DEMUX (CWDM-MUX-4-SFx=) allows you to multiplex/demultiplex four separate channels into one strand of fiber. Dual fiber is used for the connections to the GBICs and single fiber is used for the network connections. The two models (CWDM-MUX-4-SF1= and CWDM-MUX-4-SF2=) must be used together to create a four-channel single-fiber point-to-point link. This module uses the same CWDM GBICs as all of the other CWDM.

Tips: CWDM GBIC is a hot-swappable input/output device that links your switching module to the CWDM passive optical system using a pair of single-mode fiber optic cables. You can connect your multiplexed/demultiplexed wavelengths and added/dropped channels to CWDM GBICs that are installed in your system.


DWDM OADM

DWDM OADM is designed to optical add/drop one multiple DWDM channels into one or two fibers. DWDM Optical Add & Drop is the ideal solution for the increasing bandwidth demand on enterprise and metro access networks. ESCON, ATM, Fiber Channel, Gigabit Ethernet are supported simultaneously, without disturbing each other.

FiberStore DWDM OADM modules are available in standalone 19" Rack Mount, LGX module and Field module packing. No matter your network has one or two fibers, redundant network, ring or linear network design etc, we can supply best OADM configurations to tailor fit your network architect. More information, please contact our sales.

Features of CWDM/DWDM OADM