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The most common way of transporting optical traffic between two sites is by using a dark fiber pair — one individual fiber strand used for transmitting data and another to receive data. 

Light beam
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Wave Division Multiplexing (WDM) is an optical transport technology that divides existing dark fiber into multiple channels of traffic to simultaneously transport several streams of data — like increasing the number of lanes on a highway to make the flow of traffic more efficient.

As a result, public sector organizations, utilities, healthcare providers, financial institutions, corporate enterprises and data center operators are considering optical transport to be the solution of choice for their mission-critical networks. 

WDM networks use multiple colors of light, or wavelengths, over the same common path (fiber). Optical transmitters tuned to specific wavelengths send light into a passive combiner called a mux (short for multiplexer). 

All the wavelengths travel down a common fiber pair and are separated using a passive splitter, or demultiplexer (also called a demux). 

The figure below illustrates the process of how multiple signals flow across a WDM network. In this example, the signal flow is shown for one direction for illustration purposes. However, WDM networks are traditionally bi-directional and allow for combined and split wavelengths in both directions over a single fiber pair.

WDM diagram
Figure 1:  Wavelength Division Multiplexing (WDM) uses multiple or wavelengths, over the same transmission fiber.  Optical transmitters tuned to specific wavelengths send light into a passive optical combiner called a multiplexer. All the wavelengths travel down the common fiber and are separated using a passive optical splitter called a demultiplexer. Now each receiver at the other end of the fiber will be able to receive just its own discrete wavelength signal. 

Below is an example of a solution without WDM, where multiple dedicated fibers pairs are used for each separate service and no other traffic can be sent over the fiber.

For this type of solution, the cost of turning up additional services requires utilizing an extra available fiber pair, or possibly having to lease an additional pair each time another service is needed.

Dedicated fiber pair
Figure 2:  Without WDM, multiple services and data rates cannot share the same fiber pair.Dedicated fiber pairs are required per each separate point to point.

WDM technologies allow organizations to place equipment at either end of a fiber pair and combine multiple wavelength channels on a single fiber pair instead of using multiple separate fibers pairs for every separate service. 

Using either coarse wave-division multiplexing (CWDM) or dense wave division multiplexing (DWDM), operators can combine many different services on a single fiber by assigning a different color, or wavelength, to each service. 

Multiplexers are used to combine all these wavelengths onto a single fiber and demultiplexers are used to separate the colors farther on in the network. 

WDM Diagram
Figure 3: WDM can carry multiple protocols without having to convert them to a common signal format. A single fiber pair can carry virtually anything needed.


With the massive growth of over-the-top applications, cloud computing, mobile devices and the need for consumers and employees to have constant access to their data and applications, CWDM and DWDM optical networking solutions are rapidly being adopted by businesses as their bandwidth and distance requirements continue to rise

Thus, many organizations across industries are now operating their own optical transport networks to consolidate high rates of bandwidth and different traffic types across long distances.

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