What is CWDM (Coarse Wavelength Division Multiplexing)? - Neos

What is CWDM (Coarse Wavelength Division Multiplexing)?

CWDM wavelength

Coarse Wavelength Division Multiplexing (CWDM) is an optical networking technology that increases the bandwidth of existing networks. Learn all about CWDM, how it differs from DWDM, and whether a CWDM solution is right for your business’s network.

What is Coarse Wavelength Division Multiplexing?

Coarse Wavelength Division Multiplexing (CWDM) is a kind of Wavelength Division Multiplexing – a technology used to expand the capacity of fibre optic networks. It enables multiple data streams to be transmitted over different light wavelengths through a single fibre.

How does CWDM work?

CWDM uses a multiplexer to divide the light wavelengths into different channels, each carrying a separate data stream.

The channels are combined and transmitted over a single fibre optic cable. At the receiving end, a demultiplexer separates the wavelengths into the original channels. This allows multiple independent data streams to be transmitted over a single fibre.

CWDM is called “coarse” because the gaps between each channel's wavelengths are much larger than in Dense Wavelength Division Multiplexing (DWDM).

What is the difference between CWDM and DWDM?

Both CWDM and DWDM are technologies used to increase the capacity of fibre networks, but they divide up the available optical wavelengths differently. Here’s how they differ.

Wavelength range and spacing

CWDM and DWDM use different wavelength ranges and spacing:

  • CWDM operates in the 1270-1610 nanometre (nm) range of the electromagnetic spectrum. It usually spaces wavelengths 20nm apart.
  • DWDM operates on the C band (1525nm to 1565nm) or L band (1570nm to 1610nm). Wavelength spacing varies, but it’s far narrower than that of CWDM: 0.4nm for a typical DWDM system with up to 88 channels.

Number of channels

As DWDM wavelengths are much closer together than those of CWDM, DWDM can pack in significantly more channels:

  • CWDM typically uses eight channels but can support up to 18 or more.
  • DWDM provides up to 88 channels or more, depending on the multiplexing technique used.

The International Telecommunication Union (ITU) has standardised the nominal wavelengths and channels for CWDM (G.694.2) and DWDM (G.694.1), as shown in the comparison below.

CWDM vs DWDM: Comparing wavelengths and channels

Diagram comparing the available channels and wavelengths of CWDM (typical 8-channel plan) and DWDM (typical 88-channel plan)



CWDM wavelength spacing is not suitable for signal amplification, so its range is limited compared to DWDM:

  • CWDM is typically used for distances up to 80km (50 miles). It’s commonly used in short-haul, metropolitan or regional networks
  • DWDM wavelengths can be amplified to support transmission distances of hundreds or thousands of kilometres. It’s ideal for regional or long-distance networks.


CWDM systems tend to be cheaper to set up and run than DWDM networks:

  • CWDM’s “coarse” wavelength spacing typically requires fewer, simpler components than DWDM.
  • DWDM uses more sophisticated laser equipment to control wavelengths more precisely and amplify signals for longer distances.

Although the price difference between CWDM and DWDM equipment has narrowed, CWDM systems can be cheaper to install per kilometre than DWDM deployments.

What is CWDM suitable for?

CWDM is a low-cost, relatively high-capacity optical networking solution that’s ideal for a range of networks over shorter distances. Here are some common use cases for CWDM solutions:

Metro access networks

CWDM is often used to interconnect multiple locations in a city or metropolitan area. It’s a cost-effective technology for metro access networks or metropolitan area networks.

ISP connectivity

Internet service providers (ISPs) may use CWDM over passive optical networks to provide fibre to the premises – the “last mile” supplying ultrafast broadband to homes and businesses. In addition, ISPs may deploy CWDM to transmit data between their data centres or points of presence (PoPs).

Enterprise networks

For businesses, CWDM provides a low-cost way to interconnect different offices or data centres in a local area. For example, it can provide scalable connectivity across a business park, city or region.

Data centres

Data centre businesses require high-capacity, low-latency links between storage systems. With CWDM, they can reduce the number of fibres needed while maintaining sufficient bandwidth.

Video distribution

Broadcasters and streaming services can use CWDM to transmit multiple channels of ultra-high-definition content over a single fibre. Similarly, CWDM may be suitable for interconnecting local video surveillance systems.

Overall, CWDM offers a simple way to increase your fibre network’s capacity using existing infrastructure. However, DWDM can give you far more channels, longer distance connections and greater bandwidth.

Optical wavelength solutions for your business

Ultimately, your choice of networking technology depends on your business needs and budget. If you’re looking to upgrade your network to meet the ever-increasing bandwidth demands of AI, 5G and IoT, we can help.

At Neos Networks, we’re helping businesses nationwide transform their networks with Optical Wavelengths up to 400Gbps and other high-capacity connectivity, so get in touch.


We’ll be happy to design a scalable network to future-proof your business.

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