Passive CWDM vs Active CWDM

Coarse Wavelength Division Multiplexing (CWDM) is an optical multiplexing technology used for increasing the bandwidth of fiber. It works by combining optical signals of different wavelengths on one strand of fiber. Usually, CWDM is able to transport up to 18 wavelengths with a channel spacing of 20 nm in the spectrum grid from 1270 nm to 1610 nm. It is typically deployed in point-to-point topology in enterprise networks and telecom access networks. CWDM can be divided into passive CWDM and active CWDM. This article will detail these two CWDM solutions.

passive CWDM vs active CWDM

Figure 1:CWDM system

What Is Passive CWDM?

The passive CWDM is an implementation of CWDM that uses no electrical power. It separates the wavelengths using passive optical components such as bandpass filters and prisms. CWDM Mux/Demux is the most commonly used device in the passive CWDM system. It can be applied in many fields, including Gigabit Ethernet, SDH, ATM, servers, SAN, and TDM. Actually, most CWDM devices are passive and more and more manufacturers are promoting passive CWDM to deploy fiber to the home now.

What Is Active CWDM?

The active CWDM network is built from transponders and muxponders. It utilizes a dedicated transport platform that offers many functions such as signal monitoring, regeneration, and demarcation. Active CWDM solution is able to connect fast Ethernet switches, ATM switches, gigabit routers and others. It is usually applied for the communications operators and large customers to optimize or reform the network. And now it is also an ideal choice for the growing metropolitan area network.

Passive CWDM vs Active CWDM

Both passive CWDM and active CWDM have their own pros and cons.

Pros and Cons of Passive CWDM

Passive CWDM is popular mainly for the following reasons:

Easy installation – Passive CWDM installation is very simple. It is plug and play.

Independence – Passive CWDM is full independence from transmission speed and transmission protocols such as 1GbE or 1G FC.

Even though passive CWDM has the two main benefits, it still has the drawback.

Uneasy management – Due to the development of network, passive backbone networks grow as well that CWDM optics may disperse in several different layer-2 switches, routers and ADMs at different physical locations or departments of organization. This results in difficult maintenance and management.

Expensive – The requirement of passive CWDM solution that uses venspecific optics such as optical module is often very expensive.

Lots of limitations – Passive CWDM is only effective in point-to-point topology. It also has limited link power budget and distance. Moreover, passive CWDM has limited optical performance monitoring and fault isolation, which will increase MTTR.

Pros and Cons of Active CWDM

There are several advantages of active CWDM:

Cost savings – Active CWDM uses standard inexpensive cost optics and low vendor specific colored optics. What’s more, it uses muxponder capabilities (mapping multiple services over a single wavelength), which enables better spectral efficiency of the backbone network infrastructure. This significantly reduces the cost. In addition, active CWDM infrastructure enables organizations to provide managed services with SLA to its partners and customers and to generate revenue from its network infrastructure. This helps active CWDM organizations reduce operational costs.

Easier management – Due to fewer wavelengths are used between the backbone sites, active CWDM is easy for network management.

More flexibility – Unlike the passive CWDM, active CWDM is not limited by the network topology and distances between the sites. Besides, active CWDM allows for flexible add or drop capabilities as well as traffic regeneration at different points across the backbone infrastructure.

Despite these advantages, the active CWDM has a challenge:

Complex configuration – There are many more components in active builds. For instance, active CWDM usually needs transponders, which can help reach longer distance.


After the comparison of passive CWDM vs active CWDM, we can see that each one has its advantages and disadvantages. Which to deploy depends on the actual needs. Hope what we discussed in the article could help make an informed decision. If you want to know more details, welcome to visit FS.COM.

Related Article: CWDM – Cost-Effective Alternative to Expand Network Capacity

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