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The technology of combining a number of optical wavelengths and then transmitting the same through a single fibre is called wavelength division multiplexing (WDM). Conceptually, the technology is similar to that of frequency division multiplexing (FDM) used in analogue transmission. Dense wavelength division multiplexing (DWDM) is anew born multiplexing technology in the fibre optic transmission, bringing about a revolution in the bit rate carrying capacity over a single fibre. The emergent of DWDM system is one of the important phenomena in development of optic fibre transmission. This article gives introduction of DWDM technology. The demand of bandwidth is increasing day by day, especially for data traffic. Service providers are required to provide the bandwidth dynamically and in shortest possible time. This can only be done by DWDM. In future advanced DWDM components will be available. Thus, it will be possible to manage the optical signal dynamically, which will allow more flexibility to the service providers..

Dense Wavelength Division Multiplexing

Abstract
There has always been a technological talent to fulfill the constant need to extent the capacity of communication channel and DWDM (Dense Wavelength Division Multiplexing) has dramatically brought about an explosive enlargement of the capacity of fiber network, solving the problem of increasing traffic demand most economically.DWDM is a technique that makes possible transmission of multiple discrete wavelengths carrying data rate as high as fiber plant allows over a single fiber unidirectionally or bidirectionally. It is an advanced type of WDM in which the optical channels are more closely spaced than WDM.

Dense Wavelength Division Multiplexing

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MULTIPLEXING (also known as muxing) is a method by which multiple analog message signals or digital data streams are combined into one signal over a shared medium.
A device that performs the multiplexing is called a multiplexer (MUX), and a device that performs the reverse process is called a demultiplexer (DEMUX).

DWDM Components

Transmitter : Laser with precise stable waveleng-th.
Link: Optical fiber that exhibits low loss and transmission performance in relevant wavelength spectra.
Receiverhoto detectors and Optical demultiple-xers using thin film filters or diffractive elements.
Optical add/drop multiplexers and optical cross connect components.

DWDM: Key Issues

Dense WDM is WDM utilising closely spaced channels
Channel spacing reduced to 1.6 nm and less
Cost effective way of increasing capacity without replacing fibre
Commercial systems available with capacities of 32 channels and upwards; > 80 Gb/s per fibre
Allows new optical network topologies, for example high speed metropolitian rings
Optical amplifiers are also a key component

Is DWDM Flexible?

DWDM is a protocol and bit rate independent hence, data signals such as ATM, SONET and IP can be transmitted through same stream regardless their speed difference.
The signals are never terminated within the optical layer allows the independence of bit rate and protocols,allowing DWDM technology to be integrated with existing equipment in network.
 Hence, there’s a flexibility to expand capacity within any portion of their networks.

Is DWDM Expandable?

“ DWDM technology gives us the ability to expand out fiber network rapidly to meet growing demands of our customer”, said Mike Flynn, group President for ALLTEL’s communications operations.
DWDM coupled with ATM simplifies the network, reduce network costs and provide new services.
They can add current and new TDM systems to their existing technology to create a system with virtually endless capacity expansion