Passive DWDM vs. Active DWDM

Updated on Jan 12, 2024 by

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Dense Wavelength Division Multiplexing technology is divided into two primary types: passive DWDM and active DWDM. Passive DWDM and Active DWDM, both based on DWDM technology, can aggregate and transmit multiple signals of different wavelengths over the same optical fiber. To better understand the features of these two DWDM systems, the following will learn what passive DWDM and active DWDM systems are, and introduce their advantages and disadvantages.

Passive DWDM vs. Active DWDM, What's the Difference?

Passive DWDM

In a passive DWDM system, passive dwdm equipment such as passive multiplexers and demultiplexers are employed to combine and separate signals of different wavelengths transmitted along the same optical fiber. Since passive DWDM system have no active components such as EDFA, the transmission distance is limited by the transmit power of the optical modules. Consequently, in general, passive DWDM systems are more suitable for data transmission within 40 kilometers. While the transmission distance of passive DWDM systems cannot be extended, they offer the advantage of high channel capacity. We can gain insight into common passive DWDM systems from the diagram below. Clearly, active components such as fiber amplifiers are not used; instead, a pair of 20 channels DWDM Mux Demux is employed. This design is conducive to large-capacity transmission and allows capacity expansion. In other words, the passive DWDM system is more suitable for metropolitan area networks and high-speed communication lines with higher channel capacity requirements.

Active DWDM

"Active" implies that the system uses active components to sustain and manage signals transmitted through the optical fiber. In addition to the DWDM Mux Demux, active DWDM systems typically include key components such as EDFA and DCM. These components have the ability to amplify or compensate for signal attenuation and distortion during transmission, enabling active DWDM systems to support longer transmission distances (≥40 km). Due to their active nature, managing and controlling optical signals in active DWDM networks is more straightforward. The diagram below presents a design of an active DWDM system for your reference.

The link length of an active DWDM system is not only dependent on the number of optical fiber amplifiers and the signal-to-noise ratio (OSNR) but is also influenced by optical signal dispersion. Therefore, in the design of an active DWDM system, consideration should be given to the dispersion of optical signals. If necessary, dispersion compensation modules (DCM) can be added to the active DWDM system. It is important to note that dispersion compensation modules (DCM) can increase the insertion loss of the optical fiber link, affecting the transmission distance of the active DWDM system.

Passive DWDM vs. Active DWDM, How to Choose?

The benefits and limitations of passive DWDM and active DWDM are obvious to tell based on the abovementioned inherent natures, which has influences on the selection between passive DWDM and active DWDM.

Pros and Cons of Passive DWDM

Advantages	Disadvantages
Ease of setup Plug and play. No need to adjust wavelengths, making it simple and convenient to use. Cost-effective Solution Fewer components & less engineering time. The high-channel capacity feature will save the expenses substantially.	Limited Scalability The DWDM network is restricted to colored optics and fewer wavelengths on the transport fiber. Thus, more passive components will be adopted when expanding as the network grows. However, the more passive dwmd equipment, the more difficult to manage. Inconvenient Control If you need to change a wavelength or connection, you must halt usage and disconnect physical cables.

Pros and Cons of Active DWDM

Advantages	Disadvantages
Increased in Capacity A single optical fiber can accommodate more wavelengths, allowing it to carry more bandwidth compared to passive signals of the same size, thus increasing fiber utilization. Ease of management Users can dynamically adjust wavelengths without shutting down the system, enabling better control of the optical fiber network. Easier for Scalability Normally, active DWDM can be easier to scale as the network grows.	Expensive in Costs The overall active DWDM setup fees are much more expensive compared to passive DWDM solutions. Complex in Configuration There are many more components involved in active builds. Thus, the configuration will be a serious undertaking and require a solid understanding of optical networks.

Advantages

Disadvantages

Increased in Capacity
A single optical fiber can accommodate more wavelengths, allowing it to carry more bandwidth compared to passive signals of the same size, thus increasing fiber utilization.
Ease of management
Users can dynamically adjust wavelengths without shutting down the system, enabling better control of the optical fiber network.
Easier for Scalability
Normally, active DWDM can be easier to scale as the network grows.

Expensive in Costs
The overall active DWDM setup fees are much more expensive compared to passive DWDM solutions.
Complex in Configuration
There are many more components involved in active builds. Thus, the configuration will be a serious undertaking and require a solid understanding of optical networks.

When choosing between passive DWDM and active DWDM, several factors typically come into play: transmission distance, network scalability, link planning, and costs. If there are no explicit requirements for transmission distance and network upgrades, a passive DWDM solution that is easy to configure and cost-effective may be considered. On the other hand, if long-distance transmission and ease of future network upgrades are essential, an active DWDM solution can be chosen. If difficulties arise during the selection and deployment process, seeking assistance from a professional solution team is advisable.

Brief Summary

In summary, Passive DWDM is often used for shorter distances(≤40km) without a need for signal amplification, or where you want a simple, low-cost solution. In contrast, Active DWDM is used when you need high-capacity, long-haul transmissions(＞40km) with better control and the ability to maintain signal integrity over greater distances. No matter passive DWDM or active DWDM, choose the one that suits your network best.