CWDM and DWDM: What’s the Difference and How Do You Choose?

WDM technology can be a reliable, cost-effective method of solving fiber exhaust problems and expanding bandwidth across campuses, municipalities, school districts, and other networks. In our first installment, we covered the basics behind WDM technology and how it works. In this installment, we will discuss how to begin deciding which WDM is right for you, as well as addressing some common misconceptions about this incredibly valuable technology.


Deciding between CWDM and DWDM is a complex issue, with many network- and application-specific variables that need to be considered. While we recommend a consultation with an expert to get a definitive answer, here are some preliminary considerations:

Differences between CWDM and DWDM

Common Misconception 1: WDM is extremely expensive to install.

For many network operators, the concept of “WDM” is inextricably linked with large, complex active line systems that cost up to hundreds of thousands of dollars. For most applications, this is a case of up-selling by their OEMs. In fact, you can reap many of the benefits much more cost-effectively with a passive filter system. As an example, passive CWDM and DWDM systems can be monitored via the tap (or monitor) port on the face plate of most filters.

Common Misconception 2: WDM can only cover long distances.

Network operators are often discouraged from adopting a passive WDM system because the rated distances of the transceivers are much longer than required. For example, the shortest rated distance for CWDM transceivers is 40km, and 80km for DWDM transceivers. Is it still possible to use these optics if the buildings on your campus are only, say, 8km, or even 100m apart?

The answer is yes! With the proper level of attenuation on the transmitting side of your transceivers, you can still deploy a passive WDM solution to add services and conserve fiber.

Further Reading

For more information about different WDM strategies and how to use them, you can check out our coverage on our ZS line of standard passives, this application note on some simple passive architectures, and an overview WDM strategies using a single strand of common fiber.

You can also schedule a consultation with our experts, who will walk you through your options step by step and find the perfect solution for your network.

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