CWDM vs. DWDM: 4 Crucial Differences You Should Know

Introduction to Wavelength Division Multiplexing (WDM)

CWDM or Coarse wavelength division multiplex is a variant of multiplexing that is usually necessary for optical transmission on shorter distances. The other available variant, DWDM or Dense wavelength division multiplexing, is another type of technology that uses various light wavelengths to merge several streams of information onto one optical fiber and helps transmit information over much longer distances.

Prior to really understanding what is WDM, let’s start with the explanation of the wavelengths.

Understanding Wavelengths

To understand the wavelengths, let’s initially start with the technology that is used, it is called fiber optics. In this technology, the signaling medium is light or if being more specific – electromagnetic radiation.

The wavelength is necessary for the measuring of the distance between 2 photons in the light beam, whereas frequency is necessary for the specification of the time between 2 signals. The higher frequency occurs when there is a shorter wavelength and thus less time is needed between signals.

That means the frequency and wavelength characteristics can be used for the measurement of physical limitations for signal processing. So, equipment that is smaller than wavelength cannot be used.

For the transmission of data over long distances the lasers are used in fiber optics and that understanding is crucial for the creation of the fiber optics.

Overview of Wavelength Division Multiplexing (WDM)

In the WDM technology, the process functions due to the usage of a multiplexer (data selector) for the combining of different data streams and transmuting them in the wavelengths. After the transmission of these wavelengths, they are demultiplexed at the side of the receiver, where they are converted into data streams.

That means with the help of WDM, it is possible to transmit various signals on one fiber by using different light colors. Because of the usage of this technology, it is possible to increase the data quantity that can be received/sent. Also, this technology allows bidirectional transmission.

Different colors of light are determined based on the wavelength and frequency. Where the wavelength specifies the space between 2 peaks in the wave. The frequency measures the number of times a wave cycles.

Depending on the material being used, the speed characteristics might differ a little or a lot. For the proper speed measurements, the same characteristics of wavelength and frequency are used. Now, that we have understood how WDM works, let’s continue with other explanations.

Exploring CWDM Technology

CWDM technology starts with the same principle as WDM and transmits various signals over one fiber with the usage of different light colors.

Before 2002, this technology had no specific measurement and was referring to various channel configurations. Nevertheless, the Telecommunication Union standardized this technology somehow and now it relates to the wavelengths between 1,270 nm and 1,610 nm and the channel spacing is 20 nm.

The total optic span of this technology is 60 km for a 2.5 Gbit/s signal. In this standard, the frequency requirement was also not extremely fixed.   

Understanding DWDM Technology

Similarly to CWDM, DWDM technology functions by transmitting various signals in one fiber by using different colors of light.

The standard spectrum band for this technology starts from 1,530 nm to 1,625 nm, or C- and L-band, to input 40, 88, 96, or 160 channels on one fiber.

For the accommodation of more channels, this technology applies tighter wavelength spacing. That means the width for each channel is only 0.8 nm. In the CWDM technology, a wider range is used so each channel is located farther apart. DWDM can have a higher number of channels and more data in one fiber cable.

DWDM technology also uses EDFA and that helps to enhance the signals. With EDFA, it is possible to boost several signals at once. Lots of organizations prefer to use DWDM because it is possible to transmit more data and there is no need to replace other network hardware. And EDFA also plays a crucial role by amplifying different signals.

Generally, DWDM technology can help to minimize spending by using the same network equipment.

CWDM vs. DWDM: 4 Major Differences

Both these technologies are great for transmitting information over long distances and help to optimize performance, but there are some differences that we will deeply discuss in the next part of the article.

1. Transmission Capacity Comparison

CWDM is a type of technology that has simultaneous 2-way transmission of data. The major difference between these technologies is that CWDM uses laser signals which diverse in 20 nm increments.

CWDM supports 18 channels and the wavelength starting from 1,610 nm. One more difference between these 2 technologies is in “chromatic spacing”. More data can be transmitted with the help of DWDM; however, its price is way higher. That occurs because this technology requires the usage of a more precise laser design.

DWDM supports more channels when compared with CWDM. The technology can support denser packing of signals so that data can be transmitted at the rate of 100 Gbps.

2. Key Component Differences

When speaking about CWDM technology components, then the major components are the drop/insert module, Mux/Demux, and drop/pass module. The initial component is Mux/Demux which is necessary for the combining of various channels onto one fiber.

The drop/insert component gives 2 local interface ports. This component is necessary for the creation of a viable ring network even during the breaks. Drop/pass functions by removing specific channels from the fiber so that others could go through other network nodes. With the help of this component, it is possible to create a point-to-point connection.

Now let’s proceed to the component of DWDM which consists of Mux/Demux, transporter, optical add/drop, and optical amplifier. Let’s discuss the process of transmission in detail:

• The router receives the stream of data and then goes to the transponder.
• The received signal is mapped to wavelength and then goes to Mux to create an optical signal.
• Then the optical amplifiers help to enhance the signal so the data will be transmitted over longer distances.
• OADM is necessary for removing/adding bitstreams. Additional amplifiers can be used to increase signal distance.
• Then the signal gets to Demux and the signal is divided into individual wavelengths. They are transmitted via the transponder and then converted before the final destination.

3. Common Use Cases and Applications

The most standard case scenarios of CWDM usage relate to the cable television network. This technology is beneficial for minimizing interference and improving the quality of the signal.

CWDM is also used in transceivers such as SFP optics and GBIC. Such systems use standardized wavelengths for multiplexed transport. The usage of passive CWDM doesn’t require electrical power. The usage of CWDM is considered to be a more economical variant and is a fantastic option for transport devices and optical routing.

As for the standard usage of DWDM, it is specifically necessary for apps with high bandwidth, long-distance, and high-security standards.  The businesses that relate to cable and telecommunication will benefit from this technology the most.

Also, DWDM is used in colocation data centers and hyperscale cloud centers. That occurs because the technology can unite various services with independent tenants.

4. Advantages and Benefits of Each

CWDM is considered to be the easier choice when talking about management and deployment because it requires fewer optical components. Moreover, the spending can be minimized with the usage of this technology, because it uses wider wavelength spacing.

CWDM systems mainly use 8, 16, and 32 channels while DWDM uses 96 channels. That’s why the choice of technology is a rather individual thing where not all need to pay extra for unnecessary channels.

The cost of CWDM can be way lower, also because of the usage of DFB lasers and optical filters that are just cheaper. The upgrading of this system is also considered to be very economical.

The major benefit of DWDM is its ability to transmit huge volumes of information for a rather long distance. Moreover, this technology can be also deployed on the current fiber. The technology doesn’t have interference among channels and due to this, it is possible to transmit various types of information.  

Conclusion: Choosing Between CWDM and DWDM  

DWDM and CWDM are various technologies, but they should not be considered rivals. They are equally important and are necessary in optical networking. As a result, both technologies are used in the corporate, public sectors, data center apps, and healthcare.