A General Overview of Passive and Active CWDM Technology

Wavelength division multiplexing (WDM) has emerged as a popular term in recent years. WDM is further distinguished into CWDM and DWDM. Of these, CWDM stands for coarse wavelength division multiplexing and DWDM for dense wavelength division multiplexing. CWDM combines multiple laser beam signals of different wavelengths for fiber optic transmission on a single fiber. CWDM has fewer channels than DWDM and both these technologies are used to increase the bandwidth of fiber optic cables. The multiplexing is conducted using a suitable multiplexer such as CWDM multiplexer and DWDM multiplexer. Of these, the CWDM SFP Modules are common multiplexing technology employed in telecom access, enterprise, and city networks. This technology is further distinguished into passive CWDM and active CWDM. How do these passive and active components differ? Read the post to know the answers.
General Overview of Passive and Active CWDM Technology

A General Introduction to CWDM

Gaining a basic understanding of CWDM will help you understand active and passive sections better. The following pointers will be helpful in this case.
  • CWDM can transport up to 18 wavelengths between 1270 nm and 1610 nm over a single strand of fiber.
  • The wavelengths have a channel spacing of 20 nm and a channel width of 13nm.
  • This small channel spacing enables the utilization of cost-effective lasers.
  • CWDM technology is less expensive than DWDM technology, and it enables enterprise users to expand their networks without making big investments.

Passive CWDM and Active DWDM Described Briefly

Having known the CWDM technology, next comes the distinction between passive CWDM and active DWDM. This section introduces you to these terms and their effectiveness.
  • Passive CWDM: This technology uses no electric power, rather the wavelength separation is performed using prisms and bandpass filters. CWDM mux/demux is the type of passive CWDM device, and it can be used in servers, SDH, Ethernet devices, ATMs, TDMs, and so on. Today, most CWDM multiplexers found in the market are passive, and in recent years the demand for these devices has increased as manufacturers are trying to sell them to the home audience.
  • Active CWDM: As the name suggests, these devices use active components like muxponders and transponders. The devices of this type feature an active transport platform that can perform functions such as demarcation, signal monitoring, regeneration, and so on. This technology is used to connect ATM switches, routers, fiber optic network switches, and so on. The devices are more expensive than passive ones, which is why they are used by large enterprises and communication operators to transform or optimize their existing networks. Nowadays, active CWDM devices are widely used in metropolitan area networks (MANs).
Today, the performance of the fiber optic network is controlled by coarse wavelength division multiplexing (CWDM) techniques. It is important to understand this technology and its types better before investing in it. The previous post offered you brief insights on active and passive CWDM, while this post aims to help you with the right selection.

Passive CWDM vs. Active CWDM: Which One to Choose

As the basic differences between these technologies and devices powered by them may be clear now. There can be confusion regarding their selection. The pointers in this section will help you with the right selection.

Advantages of Passive CWDM

  • Easy Set-up: The technology uses fewer components, which makes the setup easy. The device usually is plug and play type, which makes the installation easy and requires no programming.
  • High MTBF Rates: It requires no cooling or power components, which makes it easy. The estimated mean time between failures (MTBF) of passive CWDM components is 500 years. MTBF predictions are usually made to address the failure rates of different components in a device.
  • Independent and Flexible: Unlike other WDM technologies, passive CWDM is independent of any transmission speed as well as protocols, which further simplifies its use. Owing to its transparent and independent nature, the CWDM multiplexer can accommodate a wide range of technologies across various channels on the same fiber.
  • Cost-effective Solution: Data can be transmitted over 18 channels in a single fiber strand up to 40 km, which helps make annual savings of $4K-$72K in city networks, and from $1 to $22K in enterprise networks.

Disadvantages of Passive CWDM

  • The passive CWDM multiplexers use optical transceivers, which make the devices expensive.
  • The multiplexers of this type possess limited link power budget and distance, and its simple to use design makes performance monitoring difficult.
  • CWDM optics in the multiplexer is difficult to monitor and manage, which is perceived as a major obstacle while implementing this device.

Advantages of Active CWDM

  • Enables Short Range to Long Range Conversion: They are standalone DC or AC powered components, which are separated from the system. They usually take the short-range optical output of the switch as input and convert them into long-range WDM signal. This conversion is enabled by a transponder and the converted signal is fed to multiplexers and transceivers.
  • Cost Efficient: Unlike passive CWDM, the active CWDM uses cheaper optics, which makes them affordable. Possessing muxponder capabilities, these devices form the backbone of enterprise networks. Muxponder capabilities mean mapping multiple wavelengths on a single fiber. This significantly helps reduce the operating costs.
  • Additional Revenues: This CWDM infrastructure allows service providers to deliver managed services to their customers and business partners and earn additional revenues.
  • Flexibility: Like passive CWDM, active CWDM also offers a certain level of flexibility. One can add or improve the capabilities and attempt traffic regeneration at multiple points within the infrastructure.

Disadvantages of Active CWDM

  • Although the separation between the systems from the actual switch enables long-range conversion, it also makes the fiber optic network switches network system more complex.
  • There are several components involved in an active configuration, which may make troubleshooting a bit complex.
  • This configuration requires a serious and in-depth understanding of optical networks.
Knowing the differences between passive CWDM and active CWDM is not enough to realize their benefits. It is important to choose high-quality CWDM multiplexers if you wish to scale your existing fiber optic network. Owing to their increasing use, today, it is easy to find these devices from different brands. VERSITRON, a leading manufacturer of fiber optic products in the US, also provides CWDM multiplexers in different specifications. The company also provides different types of fiber optic products such as media converters, network switches, fiber optic modems, and so on. These products have been part of robust fiber optic networks for several years now.  

Rich Tull

R.W. Tull is the President of Versitron Inc. He works closely with clients to review layout diagrams and drawings in order to ensure that the best fiber optic solution is achieved for a particular project.

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