Coarse and Dense Wavelength Division Multiplexing: Explained

August 15, 2018

Wavelength Division Multiplexing (WDM) uses fiber optic cables to transmit a large number of data streams. This is favoured over the conventional use of Frequency Division Multiplexing (FDM) and Time Division Multiplexing (TDM) systems. There are two main types of WDM technologies used today: Coarse Wavelength Division Multiplexing (CWDM) and Dense Wavelength Division Multiplexing (DWDM). This article explores the key differences between the two technologies and explains where and why they are used within telecommunications networks.

You may also be interested in our article: ‘Understanding Multiplexing in Telecommunications’

Introduction to Coarse and Dense Wavelength Division Multiplexing

CWDM and DWDM technologies are independent of protocol. This means that any mix of data, storage, voice or video can be used on different wavelength channels. CWDM allows up to 18 channels of data to be transmitted over a single dark fiber, whereas DWM supports up to 88. The key difference in terms of fiber is in how the transmission channels are spaced along the magnetic spectrum.

The capacity of data streams that can be sent via fiber cables has meant that WDM has become a very popular technique for modern telecommunication companies. Transmitting through WDM is possible because the method combines numerous data signals on laser beams at different infrared wavelengths along transmission lines.

Coarse Wavelength Division Multiplexing

CDWM allows up to 18 data channels to connect over a single dark fiber pair. Most commonly, there are two wavelength regions that are associated with CWDM: 1310nm and 1550nm, although the latter is more popular because it suffers less loss on the fiber (meaning the data can travel further). Each channel is set 20nm apart.

When the network distance is 80km or less, CWDM is a great solution that is both low-cost and relatively easy to deploy. If the distance required is greater than 70km then CWDM signals cannot be used. This is because it is not possible to amplify CWDM signals.

Dense Wavelength Division Multiplexing

DWDM allows up to 88 data channels (each set 0.8nm apart) and is capable of handling higher speed protocols, up to 100Gbps per channel. DWM operates within the 1550nm region of the fiber, this is because this area has the lowest loss. The 1550 region is in a stable, low-loss ‘valley’ surrounded by areas of high loss on either side. On either side of the 1550 region, the loss of the fiber quickly increases and becomes unusable for optical networking applications.

Not only does DWDM have greater channel capacity in comparison to CWDM but it is also possible to reach greater distances (up to 80km). Not only that, but with amplification the signal to support much longer distances of up to 1000km or more.

Comparison: Which technology should you use in your network?

Distance 70km unamplified 80km unamplified
1000km+ amplified Not applicable
Channels  88 (Using interleaver) 18 (Distances limited in the water peak)
Spacing 0.8nm 20nm
Protocols All including 100G and beyond: 1/10/40/100GE and 8/16/32GFC Up to 10GE and 8GFC
(40G using 4x10G CWDM)


There are a number of benefits to each solution which depend on the requirements of the network. If for example, a CWDM solution is already being utilised within the network and it holds further capacity for growth, then CWDM should definitely be considered. However, if the network is reaching capacity, then you may want to consider redeploying a DWDM system with higher capacity.

Traditionally, DWDM systems were designed and used by telecommunication operators for fixed systems and therefore required large operating centers. For that reason, CWDM was the preferred choice for corporate data center connections. Now there are solutions for DWDM at the data center level which allow more choice for telecommunication companies.

At Carritech, we actively source and supply, as well as repair parts for CWDM and DWDM systems all around the world. Our customers rely on our industry knowledge, particularly in the area of hard-to-find products.

If you operate a network that relies on CWDM or DWDM systems to serve your customers or staff, click here to find out more about our services and how we can partner with you to ensure your network is the best it possibly can be.

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