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What is WDM (Wavelength Division Multiplexing) for fiber optic communications? Fiber Optic Tutorial

WDM is short for Wavelength Division Multiplexing. What it does is divide the light in an optical fiber into several discrete wavelengths (colors). Each wavelength (color) is an independent channel running at a data rate of 2.5 Gbit / s, 10 Gbit / s, 40 Gbit / s, or even 100 Gbit / s (still under development). So if the light in the fiber is divided into 16 wavelengths (colors or channels), and each wavelength runs at a data rate of 40 Gbit / s, we get a total of 40 Gbit / s x 16 = speed 640 Gbit / s. This is especially true of long-haul and ultra-long-haul fiber optic communication links.

Furthermore, fibers carrying 64 or more channels (wavelengths) are already available on the market. Which means that we can run a data rate of 2,560 Gbit / s on a single fiber. How about 48 fibers in a single fiber optic cable? That gives us an incredible 2,560 Gbit / s x 48 = 122,880 Gbit / s link. Of course, these types of high-speed, high-fiber-count links are generally only implemented for Internet backbones.

From the aforementioned samples, you can see the shocking truth about WDM. Dramatically increases the capacity of a fiber optic link while minimizing the cost of fiber optic cable and equipment.

What is DWDM?

DWDM stands for Dense Wavelength Division Multiplexing. Here “dense” means that the wavelength channels are very narrow and close to each other. For dense 100 GHz WDM, the adjacent channel interval is only 100 GHz (or 0.8 nm). For example, the adjacent channels could be 1530.33 nm, 1531.12 nm, and 1531.90 nm.

DWDMs are widely used for the 1550 nm band to take advantage of the capabilities of EDFA (Erbium Doped Fiber Amplifiers). EDFAs are commonly used for 1525nm ~ 1565nm (C-band) and 1570nm ~ 1610nm (L-band).

Why is DWM so important?

The exploitation of DWDM has caused an explosion in transmission capacity. The amount of information that can be sent over fiber cables that run around the world has increased so much that there is now excess capacity available.

In practice, more can be extracted from DWD systems by extending the upper or lower limits of the available transmission window or by spacing wavelengths more closely, typically at 50 GHz, or even 25 GHz. By doing this, providers they can double or triple the number of channels. Currently, each optical channel can be used routinely for the transmission of light pules at 10 Gbit / s, or even higher data rates with 100 GHz spacing. With the help of WDM, a pair of fibers can provide a data capacity of several hundred gigabits per second.

WDM technology does not require any upgrade or replacement of the fiber infrastructure that has been installed. Therefore, we can upgrade the links from one capacity level to the next simply by reconfiguring or upgrading the terminal equipment and repeaters.

WDM technologies provide the raw transmission capacity. This has to be structured in some way so that it can carry useful traffic and be routed to where it needs to go. This is where the next layer of network protocol comes into play. SDH and SONET (They are equivalent. SONET is used in the United States while SDH is used in the rest of the world). We will play SDH and SONET in some other tutorials.