What is DWDM? A Beginner Guide (2023)

Published on Nov 27, 2017, Updated on April 24, 2023

Table of Contents

• What is DWDM?
• What are the benefits?
• What are the drawbacks? 
• DWDM system components
• How to test
• DWDM solution from Optcore
• FAQ
• Final words

What is DWDM?

DWDM refers to Dense Wavelength Division Multiplexing. The technology supports multiplexed transmission of multiple optical wavelengths in a single fiber strand. Similar to CWDM, DWDM is also a form of WDM technology. However, by defining smaller wavelength spacing, it can provide the maximum number of channels, and therefore has a greater overall capacity. Hence, Dense Wavelength Division Multiplexing can rapidly increase the bandwidth capacity of existing fiber networks. 

In other words, DWDM creates multiple virtual optical fibers, increasing bandwidth on existing fiber optic backbones. More specifically, the technique multiplexes the tight spectral spacing of a single fiber carrier in a given fiber to take advantage of the achievable transmission performance (e.g., with minimal dispersion or attenuation). 

DWDM key benefits

#1 Super capacity

The current single-mode fiber can support 1Gbps, 10Gbps, to 100Gbps transmission speed. Using DWDM, the bandwidth can achieve tens or even hundreds of times without laying new fiber. There is massive scope for bandwidth expansion when considering bit rate upgrades.

#2 Investment protection

For the DWDM system, the user can expand and increase the bandwidth network by adding corresponding optical modules without layering the new fiber optic cable. Just add a new wavelength channel when carrying any new service or capacity. That provides the best investment protection for existing network facilities. 

#3 Wavelength routing

In DWDM networks, routing is achieved through wavelength selection switches to establish topological connections between nodes with different wavelengths.

#4 Reconfigurability

Through optical cross-connect (OXC) and optical add-drop multiplexing (OADM) technologies, DWDM optical transport networks can achieve dynamic reconfiguration of optical wavelength channels. At the same time, in the event of transmitter device failure, line interruption, and node failure, we can still re-route the failed channel by reconfiguring the wavelength channel so that the network can quickly achieve self-healing or recovery and ensure that the upper layer services are not affected. Therefore, Dense Wavelength Division Multiplexing optical transport networks can provide strong survivability directly on the optical path layer.

#5 Cost-effectiveness

DWDM systems offer a low total system cost of ownership. That is mainly because it significantly optimizes the efficiency of single-strand fiber usage and allows the supplier to avoid laying new fibers. This results in significant material cost savings for laying new fibers and considerable labor cost savings.

#6 Scalability

DWDM can use the abundance of dark fiber in many metropolitan areas and enterprise networks to swiftly meet the demand for capacity on point-to-point links and spans of existing SONET/SDH rings.

#7 Transparency

A key advantage of DWDM is that its protocol and transfer speed are irrelevant. DWDM-based networks can use the IP protocol, ATM, SONET / SDH, and Ethernet protocol to transmit data, processing data traffic between 100Mbps, 1.25Gbps, and 10Gbps. In this way, these networks can send different types of data traffic on a laser channel at different speeds. From a QoS (Quality of Service) point of view, Dense Wavelength Division Multiplexing-based networks quickly respond to customers’ bandwidth needs and protocol changes cost-effectively.

What are the DWDM drawbacks?

Although DWDM has many benefits, they do have some drawbacks. Now let us summarize its disadvantages below.

#1 Higher cost for fewer channels

Because of the very narrow frequency window maintained, DWDM laser emitters require precise temperature control of the laser emitter to prevent “drift” of the center frequency. That consequently results in a significantly higher cost for Dense Wavelength Division Multiplexing systems than CWDM systems. For some network transmission scenarios with less than 18 channels, CWDM is sufficient to cope. In this case, using DWDM often requires a larger budget.

#2 System complexity

compared with the regular fiber optic system, DWDM requires additional components like Mux/Demux, optical amplifier, and OADM for long-haul transmission. It finally increases the system’s complexity and makes it a challenge for easy management.

DWDM system components

#1 DWDM Transceiver

The DWDM transceiver is one of the most critical components of the Dense Wavelength Division Multiplexing system. Because of the tiny wavelength space, DWDM systems require exact optical wavelengths to operate without inter-channel distortion or crosstalk. Dense Wavelength Division Multiplexing transceivers have built-in fixed wavelength lasers or tunable lasers and thus emit different operating wavelengths. 

And according to the size of different wavelength spaces and channel counts can be divided into 200-GHz, 100-GHz, and 50-GHz, etc. Currently, 100-GHz and 50-GHz transceivers are the most common ones. 

100-GHz typically supports 80 channels, while 50-GHz support 160 channels. For more details, please read this article.

DWDM Transceiver is the core of the performance and cost of the whole DWDM system. Therefore, it is crucial to select the right vendor. Consider the rate and link budget supported by the transceiver and its wavelength stability and temperature characteristics. That is critical for long-distance backbone transmission.

Currently, the most common DWDM transceiver includes DWDM SFP, XFP+, SFP+, SFP28, QSFP28, etc. 

#2 DWDM Mux & Demux 

DWDM systems transmit multiple signals over a single fiber. Therefore, before the signal enters the fiber, the different wavelengths must be converged into a single beam by a multiplexer before transmission. 

At the receiving end, a demultiplexer is needed to separate the different wavelengths on a single fiber so that the photodetector can detect the corresponding optical signal.

Therefore, a complete DWDM one-way system must contain a multiplexer at the transmitter side and a demultiplexer at the receiver side. For a two-way communication system, a multiplexer and a demultiplexer are included at both ends to transmit and receive optical signals through two separate fibers.

#3 Optical Add/Drop Multiplexers

OADM is designed to insert or remove wavelengths with a specific wavelength. OADM does not merge or separate all wavelengths but removes some while passing on others. OADM performs in the optical domain what traditional SDH (electrically synchronous digital hierarchy) demultiplexers do in the time domain and is transparent enough to handle signals of any format and rate.

#4 Optical Amplifiers

Due to the optical signal attenuation, an unregenerated fiber segment can only travel a limited distance (80KM or 120KM) intact. That distances are inadequate for DWDM systems mainly used for backbone network transmission. That is where optical amplifiers (OA) come into play. 

By introducing optical amplifiers, OA can amplify the wavelength signals of all channels simultaneously, and no optical-electrical-optical (OEO) conversion is required. Hence DWDM systems can extend the transmission distance to hundreds of kilometers or even 1500 kilometers.

Aside from optical links, optical amplifiers can be employed to increase signal strength after multiplexing or before demultiplexing, both of which can bring loss into the system.

The most common optical amplifiers are EDFA and Raman amplifiers. Now let’s make a simple introduction to them.

• EDFA stands for Erbium Doped-Fiber Amplifier. It is a form of the optical amplifier with erbium ions added to the optical fiber core. It is generally employed in the C and L bands, from 1530 to 1565nm. However, EDFAs cannot amplify wavelengths shorter than 1525nm.
• Raman amplifier is another optical amplifier that can amplify signals at any wavelength. The basis of operation is based on stimulated Raman scattering (SRS). The optical fiber is undoped. The inserted photon stimulates the electron, which causes it to vibrate. The electron then de-excites the vibrational state of the glass molecules in the optical fiber, resulting in stimulated emission.

How to test the DWDM network?

DWDM networks are now widely used in data center interconnect (DCI), access, metro, and core/long-haul networks. To ensure the smooth operation of DWDM, optical power, sensitivity, loss, connector cleanliness, dispersion, and spectral quality tests are often required. These tests generally require the use of the following tools.

• OTDR: Verifies the performance of the optical test link to avoid service interruptions and locate any physical layer issues
• Channel Checker: Verify channel performance and wavelength configuration on real-time fiber links. 
• Optical Power Meter: Tests the optical power of the optical transmitter to meet specifications
• Optical Spectrum Analyzer (OSA): Measures the central wavelength, OSNR, channel power, SMSR and other characteristics
• Fiber Endface Microscope: Visually check the cleanliness of the transceiver and fiber connector end-face

DWDM solution from Optcore

As a pioneer in fiber interconnectivity, Optcore offers a complete DWDM transceiver solution for nearly all telecom, enterprise, and data center application. Our Dense Wavelength Division Multiplexing transceiver includes the below categories.

• DWDM SFP
• DWDM SFP+
• DWDM XFP
• DWDM SFP28
• DWDM QSFP28

Most importantly, we hold a massive stock for quick delivery and help the end user reduce the stock level with maximum flexibility. 

FAQ 

Q: WDM vs DWDM, What is the difference?

A: DWDM is one of the WDM technology. However, it utilizes closely spaced channels, providing much more bandwidth on the same fiber. Typically WDM technology includes BiDi, CWDM, and DWDM. 

Q: Is DWDM single mode or multimode?

A: It is single mode. DWDM typically uses the spectrum S-band, C-band, and L-band, which is only suitable for single mode fiber. 

Q: How many channels does DWDM have?

A: For 100GHz spacing, it supports 80 channels. For 50GHz spacing, it provides 160 channels. 

Q: Is it better to use DWDM or more fibers?

A: In most cases, DWDM is better. Because you don’t need to deploy any new fibers, add the transceiver, mux, and demux, and you will get more bandwidth quickly. Furthermore, it is far faster to repair a pair when the fiber is cut than to splice 50 or more strands. 

Final Words

This article provides a beginner guide to the Dense Wavelength Division Multiplexing in 2023. We have explained the definition, benefits, disadvantages, and main system components.

Now I’d like to hear from you:

Do you have any DWDM-based network?

Will you prefer CWDM or DWDM?

Either way, let me know by leaving a comment below right now.

Read more:

• Do You Know the CWDM Transceiver Color Code?
• DWDM Wavelength ITU Channels Chart: A Complete Guide
• OPTCORE Best 10G CWDM SFP+ Transceiver Solution
• Optical Wavelength Band 101: Definition, Classification and Application

Reference:

• Spectral grids for WDM applications: DWDM frequency grid
• Introduction to DWDM Technology