DWDM (Dense Wavelength Division Multiplexing, BBC)

DWDM(Dense Wavelength Division Multiplexing) is a fiber optic transmissiontechnique that works by combining and transmitting multiple signals simultaneouslyon the same fiber in a dense wavelength grid.

WDM conceptual view.

DWDMcombines multiple optical signals to one single fibber in order to amplify thetransmission and to increase its bandwidth capacity.

DWDMtechnology offers many key benefits such as:

1.    Allowing the transmission ofe-mail, video, multimedia, data and more.

2.    It is possible to use signals indifferent rate and different format (ATM, SONET/SDH, IP, Ethernet and more).

3.    A large amount of information canbe transferred.

4.    It can handle high bit-rates.

5.    Lower cost.

The optical network consists of lasers and optical fibers carryingflashers of light from the lasers. Increasing the number of lasers willincrease the bit rate. All the lasers send their light to the optical fiber atthe same time, and in order to distinguish between the sources, each flasherhas its own color (which is of different wavelength), in this way the receivedinformation in the other end of the network can be separated to its original.

With thislatest technology, individual lasers can transmit at 10 Gb/s ,and in WDMAtechnology we can have several lasers transmitting at the same time (The numberof lasers is , usually , a multiplication of 2).

Thecombination of several wavelengths together on the same fiber is calledmultiplexing; the separation called de-multiplexing .In order to detect aspecific wavelength we need to use a specific light detector.

DWDM Mux and De-Mux:

DWDM mux and de-mux.

The wavelengths of light usually vary around 1550 nanometer (in thiswavelength the loss and the attenuation consider to be low). The wavelength isa multiply of 0.8nm therefore if you have three wavelengths, It ispossible to use the following wavelengths: 1549.2nm, 1550nm and 1550.8nm.

From aQuality of Service standpoint, DWDM enables response to protocol changes andcustomers' bandwidth demands at lower costs.

DWDMSystem Structures:

 A basic DWDM system structure is build from thefollowing components

1. transmitters
2. receivers
3. EDFA
4. Add and Drop.
5. DWDM multiplexers
6. DWDM de-multiplexers.

Explanation of structure entities: 

1. Transmitters � lasers that transmit data with a very accurate wavelength � each laser is configured to transmit in  acertain wavelength

2. Receivers� components that receive the signal and transmitthem into a de-multiplexer.

3. EDFA - Erbium-Doped Fiber Amplifier. Optical repeater device that amplifies the opticalsignal. Its is silica based optical fibers that is doped with erbium that boostthe power of the wavelength.

4. Add andDrop � components that receive a fiber optic with somewavelength multiplexed, and can drop or add a certain lambda from orto the signal.

5. DWDMmultiplexers � receive many optical signals, each one indifferent wavelength, and transmit the entire wavelength in one optic fiber.

6. DWDM de-multiplexers � Receive all the signals in one optic fiber , and transmit eachwavelength in a different fiber.

Thesystem structure is shown in the following diagram:

system structure DWDM

Thediagram shows that each wavelength transmitted by the laser is inserted intothe multiplexer. The multiplexer combines allthe signals from the different fibers into one signal in the optic fiber. Theoptic fiber can be inserted to an add & drop which can take a certain lambda to its channel, or add a certainlambda from the channel. It can move through EDFA for amplifying the signal. Atthe end of the channel it is inserted to a de-multiplexer that separates the differentwavelengths into different optic fibers.