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WDM, CWDM, DWDM… what in the world do they mean? These are abbreviations for terms that are related to fiber optics, which is a kind of high-speed network connectivity method.

Here’s the gist, but we’ll get way more into their differences and benefits below:

  • WDM (wavelength-division multiplexing) is a technology that supports huge data transmissions over a single fiber optic cable.
  • CWDM (course WDM) and DWDM (dense WDM) are subsets of WDM.
  • Coarse WDM uses wider channel spacing and fewer channels than DWDM.

What Is WDM?

Wavelength-division multiplexing is a kind of technology that allows the same fiber optic cable to transmit multiple signals by using different wavelengths/colors of light.

An easier way to illustrate this is to imagine light as crayons (bear with me here…).

Imagine you have a big box of crayons, and you want to draw a picture, but you can only use one crayon at a time. To draw with multiple colors at once, you have to keep switching crayons, which can be slow and tedious. A better solution is to use a crayon holder. This allows you to hold multiple crayons at the same time, and you can switch between them quickly and easily.

WDM is like a crayon holder for light. It allows the transmission of multiple signals over the same fiber optic cable by using different colors of light. This is much faster and more efficient than transmitting the signals one at a time.

What Is CWDM?

Coarse wavelength-division multiplexing (CWDM) is a cost-effective way to increase the bandwidth of a fiber optic network without having to install additional cables. These systems typically support up to 18 wavelengths, each of which can carry a data rate of up to 10 Gbps.

This means a single CWDM system can provide a total bandwidth of up to 180 Gbps.

CWDM is often used in access networks, which are the networks that connect businesses and homes to the internet. It’s also used in metropolitan area networks (MANs) and regional networks.

Since I like to use analogies to simplify concepts, let’s do another one, but this time we’ll illustrate CWDM with a highway. Say you want to increase the number of cars that can use the highway without having to build additional lanes. One way to accomplish this is by using different colors of light to represent different lanes. For example, red might be for cars going one direction, and blue for cars going the other direction.

Instead of using different colors of light, CWDM uses different wavelengths of light to represent different channels. This allows multiple signals to be sent over a single fiber optic cable without interfering with each other.

What Is DWDM?

Dense wavelength-division multiplexing (DWDM) is super similar to CWDM. Imagine again the multi-lane highway analogy. Each lane can carry a different vehicle, and all the vehicles can travel at the same time. DWDM is like a highway with multiple lanes of light. Each lane of light can carry a different data stream, and all the data streams can travel over the same fiber at the same time.

However, while CWDM supports up to 18 wavelengths, DWDM supports up to 80. This allows DWDM networks to carry a much higher capacity of data than traditional optical networks.

DWDM uses lasers to generate light signals of different wavelengths. These signals are then combined and sent over a single fiber using a multiplexer. At the other end of the fiber, a demultiplexer separates the different wavelengths, allowing the original signals to be retrieved.


CWDM and DWDM are optical networking technologies that allow multiple signals to be transmitted over a single fiber optic cable. However, there are some key differences between the two technologies, and it is important to understand which one is right for your specific needs.

ChannelsChannel SpacingBandwidthCostTransmission Distance
CWDMUp to 1820 nmLowerLowerUp to 160 km
DWDMUp to 800.4 nm or 0.8 nmHigherHigherUp to 1,000 km

As you can see from this table, one of the biggest differences between CWDM and DWDM is the wavelength spacing between the different channels. CWDM uses wider wavelength spacing, typically 20 nanometers (nm), while DWDM uses narrower wavelength spacing. This means DWDM systems can support nearly 5 times as many wavelength channels than CWDM.

Another key difference between CWDM and DWDM is the distance over which they can transmit data. CWDM is typically used for shorter distances, up to about 160 kilometers (km). DWDM, on the other hand, can be used for much longer distances. This is because DWDM systems can use optical amplifiers to boost the signal over long distances.

CWDM systems use lasers that don’t need to be cooled. Cooling lasers use a process called temperature tuning to improve performance and lifespan, but this process also consumes more power than the electronic tuning used in CWDM lasers. In other words, CWDM lasers are simpler and cheaper to use, but they’re not as powerful or reliable as DWDM lasers.

Implementation cost is another way these two technologies contrast. CWDM systems are generally less expensive than DWDM systems because the former’s components are less complex and require less precision in manufacturing.

How are CWDM and DWDM Used?

CWDM is often used in enterprise networks and telecom access networks. It’s also a good choice for applications where a large number of channels aren’t required. Connecting data centers or remote offices are just a few examples.

DWDM is often used in core networks and long-haul networks. Due to its larger channel support, it’s also a good choice for applications where a high number of channels are required, like when connecting multiple data centers or providing high-speed internet service.

Organizations that have access to a WDM network can better support data-heavy applications like video streaming, data replication centers, and large web apps.

Which One Is Right For You?

Both technologies have their own advantages and disadvantages. While CWDM is less expensive and doesn’t require as much power, it also has lower range and capacity versus DWDM.

The best way to decide which technology is right for you is to consider your specific needs. If you need a high-capacity solution for short distances, CWDM may be a good choice. Conversely, if you need a high-capacity solution for long distances, DWDM is the better option.

You might also consider things like management complexity and scalability. CWDM are usually easier to manage, but DWDM systems are the better choice if you need a solution that can be scaled up easily.

You may also learn about network traffic analysis.

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  • Jon Fisher
    Jon has been writing about tech for over a decade. His work includes everything from software reviews to troubleshooting guides, definitions of complex technology terms, and opinion articles. His content can be seen on Lifewire, AddictiveTips,…

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