Category Archives: OADM

5 Concepts Help Easily Get WDM System


The Wavelength Division Multiplexing (WDM) system is a passive, optical solution for increasing the flexibility and capacity of existing fiber lines in high-speed networks. By adding more channels onto available fibers, the WDM System enables greater versatility for data communications in ring, point-to-point, and multi-point topologies for both enterprise and metro applications. Do you know about WDM system? 5 concepts provided in this blog may help you easily get it.

Optical Transmission
Optical transmission is the conversion of a digital stream of information to light pulses. The light pulses are generated by a laser source (LED or vessel) and transmitted over an optical fiber. The receiver converts the light pulses back to digital information.

Optical Transmission

Wavelength Division Multiplexing
WDM is based on the fact that optical fibers can carry more than one wavelength at the same time. The lasers are transmitting the light pulses at different wavelengths that are combined via filters to one single output fiber. The device used to combine wavelengths is called multiplexer and the device used to separate wavelengths is called demultiplexer, which are the two most basic component in WDM system.

Wavelength Division Multiplexing

Optical Amplifiers
An optical amplifier is a device that amplifies an optical signal directly, without the need to first convert it to an electrical signal. Optical amplifiers boosts the attenuated wavelengths and are more cost efficient than electrical repeaters. Without amplifiers the reach is limited to 80-100km before electrical regeneration. Amplifier stations typically each 80-100km.

Depending on signal types and fiber characteristics, amplifiers are used in DWDM networks and increases the reach of the optical signals up to 3000 km. Amplifiers are an basic building block for a powerful DWDM network.

Optical Amplifiers

Transponders provides wavelength conversion from client to WDM signal. A transponder maps a single client to a single WDM wavelength. The digital framing of a line signal from a transponder provides service monitoring, management connectivity and increased reach. The broad range of available transponders enables cost efficient solutions for both CWDM & DWDM.


Optical Add Drop Multiplexer
The main function of an optical multiplexer is to couple two or more wavelengths into the same fiber. If a demultiplexer is placed and properly aligned back-to-back with a multiplexer, it is clear that in the area between them, two individual wavelengths exist. This presents an opportunity for an enhanced function, one in which individual wavelengths could be removed and also inserted. Such a function would be called an Optical Add Drop Multiplexer (OADM). OADM is used for increased flexibility in the optical paths. Services can be redirected upon failure or capacity constraints and capacity can be increased dynamically per node.


Multiplexer and demultiplexer are the most basic component in WDM system. If your transmission distance is more than 100 km, an optical amplifier is necessary. If your client wavelength isn’t available for WDM applications, you may need a transponder to convert it to WDM available wavelength. Want to achieve a more flexible, just choose to use a OADM. Besides these, sometimes, a dispersion compensation module is also needed to fix the form of optical signals that are deformed by chromatic dispersion and compensates for chromatic dispersion in fiber that causes the light pulses to spread and generate signal impairment. Do you get WDM system? Just start to build your own WDM system now!

Application of Optical Add-Drop Multiplexer

What’s the Optical Add-drop Multiplexer?

An optical add-drop multiplexer (OADM) is a device used in wavelength-division multiplexing 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. An OADM may be considered to be a specific type of optical cross-connect.

A traditional OADM consists of three stages: an optical demultiplexer, and optical fiber multiplexer, and between them a method of reconfiguring the paths between the optical demultiplexer, the optical multiplexer and a set of ports for adding and dropping signals. The optical demultiplexer 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 optical multiplexer or to drop ports. The optical multiplexer multiplexes the wavelength channels that are to continue on from demultiplexer ports with those from the add ports, onto a single output fiber.

Principles of OADM technology

General OADM node can use four port model (Figure 1) 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.

Figure 1 OADM basic model

OADM node technical classification

Optical drop multiplexer network technologies can be divided into two types, fixed optical drop multiplexer (Fixed OADM, FOADM) and reconfigurable optical drop multiplexer (Reconfigurable OADM, ROADM).

Fixed Optical Drop Multiplexer (FOADM)

FOADM to filter as the main component, and its function is fixed to join or retrieve certain light wavelengths. General common FOADM can be divided into three types, namely Thin Film Filter type (TFF type), Fiber Bragg Grating (FBG type) and integrated planar Arrayed Waveguide Gratings (AWG type).

Thin Film Filter (TFF FOADM)

* TFF FOADM using thin film between the filtering effect of the different refractive index.

Fiber Bragg Grating (FBG FOADM)

* FBG FOADM use of fiber Bragg grating filtering effect, with two circulator can become FOADM.

Arrayed Waveguide Gratings (AWG FOADM)

* AWG FOADM gererally used in semiconductor fabrication processes, the integration of different refractive index material is formed on a flat substrate in a planar waveguide, when different wavelength light source is incident through the couping after the import side, due to take a different path length, while the different phase delay caused by different wavelengths and thus produce certain wavelengths in the export side to form a constructive or destructive interference, making waves in the export side, the different wavelengths will follow the design on a different channel to reach, and thus achieve FOADM function.

Reconfigurable Optical Add/Drop Multiplexer (ROADM)

ROADM can always be adjusted with the distribution network to add and drop wavelength, which reconstruct the network resource allocation, the flexibility to meet the requires of modern urban network, so a flexible ROADM features, plus optical switch substantial advantage, making the current fastest growing ROADM based voa attenuator based ROADM (switch based OADM). ROADM mainly be the optical switch, multiplexer and demultiplexer composed, Switch-based OADM, mainly divided into Wavelength independent switch array and wavelength selection switch.

Type 1 Wavelength independent switch array

Type 2 Wavelength selective switch

All kinds of optical drop multiplexer performance comparison

OADM network applications

WDM ROADM optical fiber suitable for different network environments

OADM in the metropolitan network development tendency

1. Arbitrary choice must be retrieved, adding wavelength, the wavelength can take advantage of the limited resources, the node can be retrieved with the need to do to join the adjustment of the signal wavelength, and has a remote control functions. This can provide dynamic reconfiguration of optical communications network capable ROADM will be connected to the backbone network critical devices. And FOADM is used for wavelength demand network access will be smaller parts to reduce costs. Furthermore, ROADM use to all kinds of Tunable Laser, unable Filter, or wavelength selective optical switches and other components.

2. Must be able to convert incompatible wavelength suitable for the backbone network will be transmitted wavelengths. Therefore, OADM be combined with wavelength conversioin Transponder or other functional components.

3. Must be able to compensate for the node to make acquisistion, adding such action energy loss. Therefore, OADM optical amplifiers must be combined with functional components.

4. Wavelength signals related specifications, such as: the signal to noise ratio (S/N), the energy balance between the signal wavelength, etc., are required to meet network requirements. Therefore must be combined OADM Variable Optical Attenuator (VOA), dispersion compensation module (DCM) and other components.

How Much Do You Know About OADM

The OADM, or optical add drop multiplexers, is a gateway into and out of a single mode fiber. In practice, most signals pass through the device, but some would be “dropped” by splitting them from the line. Signals originating at that point can be “added” into the line and directed to another destination. An OADM may be considered to be a specific type of optical cross-connect, widely used in wavelength division multiplexing systems for multiplexing and routing fiber optic signals. They selectively add and drop individual or sets of wavelength channels from a dense wavelength division multiplexing (DWDM) multi-channel stream. OADMs are used to cost effectively access part of the bandwidth in the optical domain being passed through the in-line amplifiers with the minimum amount of electronics.

OADMs have passive and active modes depending on the wavelength. In passive OADM, the add and drop wavelengths are fixed beforehand while in dynamic mode, OADM can be set to any wavelength after installation. Passive OADM uses fiber optic filters, fiber gratings, and planar waveguides in networks with WDM systems. Dynamic OADM can select any wavelength by provisioning on demand without changing its physical configuration. It is also less expensive and more flexible than passive OADM. Dynamic OADM is separated into two generations.

A typical OADM consists of three stages: an optical demultiplexer, an optical multiplexer, and between them a method of reconfiguring the paths between the optical demultiplexer, the optical multiplexer and a set of ports for adding and dropping signals. The optical demultiplexer separates wavelengths in an input fiber onto ports. The reconfiguration can be achieved by a cross connect patch panel or by optical switches which direct the wavelengths to the optical multiplexer or to drop ports. The optical multiplexer multiplexes the wavelength channels that are to continue on from demultipexer ports with those from the add ports, onto a single output fiber.

Physically, there are several ways to realize an OADM. There are a variety of demultiplexer and multiplexer technologies including thin film filters, fiber Bragg gratings 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.

CWDM and DWDM OADM provide data access for intermediate network devices along a shared optical media network path. Regardless of the network topology, OADM access points allow design flexibility to communicate to locations along the fiber path. CWDM OADM provides the ability to add or drop a single wavelength or multi-wavelengths from a fully multiplexed optical signal. This permits intermediate locations between remote sites to access the common, point-to-point fiber message linking them. Wavelengths not dropped, pass-through the OADM and keep on in the direction of the remote site. Additional selected wavelengths can be added or dropped by successive OADMS as needed.

FiberStore provides a wide selection of specialized OADMs for WDM system. Custom WDM solutions are also available for applications beyond the current product designs including mixed combinations of CWDM and DWDM.