Wavelength Division Multiplexing (WDM) has long been the best technology for transporting large amounts of data between data centers. This technology increases bandwidth by allowing different data streams to be transmitted simultaneously over a fiber optic network. WDM optimizes the use of optical fibers and maximizes network investments. Traditionally, WDM systems were adopted by carriers and service providers. Large-scale systems designed for national infrastructures were too expensive and complex for use on a private network. In recent years, things have changed. The technology is still evolving rapidly today. WDM network solutions are available today to meet the needs of enterprises and private data centers. The solutions are simpler and more cost-effective than traditional carrier solutions. Many organizations have yet to discover the full benefits of WDM networks, particularly in terms of leveraging network investments and getting the most out of fiber optic networks. The unique feature of WDM standards lies in the ability to send different types of data over fiber optic networks in the form of light. Thus, different light channels, each with a specific wavelength, are sent simultaneously over a single optical fiber. Instead of using multiple fibers for each service, a single fiber can be shared for multiple services. In this way, WDM increases bandwidth and optimizes the use of optical fibers. Renting or purchasing optical fibers represents a significant portion of networking costs. Therefore, using a single optical fiber to transport multiple traffic channels can generate substantial savings.

There are several types of WDM depending on the wavelengths used: CWDM for Coarse Wavelength Division Multiplexing DWDM for Dense Wavelength Division Multiplexing Both technologies work identically, the only difference is the number of channels (i.e. usable wavelengths). DWDM uses a spacing between 1.6 and 0.4 nanometers compared to 20 nanometers for CWDM, which allows for a much larger number of standardized channels (from 96 for the C band to 160 theoretical, compared to 8 or 18). DWDM uses wavelengths around 1550nm. The most used frequency range is the C band (Conventional): 191.560 to 195.942 THz (from 1565 to 1530 nm). On the characteristic curve of silica, the attenuation in the bandwidth (1530 nm - 1 565 nm) is 0.2 dB/km. This is the lowest. With new generation lasers and optical fibers, it is possible to cover distances of 80 km. CWDM mainly uses wavelengths between 1470 and 1610 nm (8 wavelengths; 18 in total have been standardized from 1270 to 1610 nm). At certain wavelengths, the attenuation is much higher ( 0.3 dB). CWDM is suitable for medium distances.

Of course, this reduced spacing (also called “step”) for the DWDM standard requires lasers and “MUX/DEMUX” that are much more precise and therefore much more expensive. The other notable difference between these two technologies is the maximum distance and throughput that can be achieved. The achievable distance is a function of what is called the optical budget: Optical budget = Transmitter power - Receiver sensitivity This optical budget must be greater than the total attenuation of the optical fiber. DWDM equipment has more precise optics than CWDM equipment, and can therefore reach longer distances for an equivalent or higher throughput. In addition, the DWDM frequency band allows amplifiers (called EDFA for Erbium Doped Fiber Amplifier) to be added to the optical fiber link, if necessary. To simplify, we can say that CWDM is suitable for a distance of less than 40km at 1Gb/s, while DWDM is capable of reaching 80km at 10Gb/s, and even more with the addition of amplifiers every 80 km. Contrary to what one might think, CWDM was developed after DWDM, precisely to offer a more economical but also much more limited solution.

Transceivers - Transmitting Data into Light WDM transceivers are lasers with a specific wavelength that convert data signals from SAN and IP switches into optical signals that can be transmitted over fiber. Each data stream is converted into a signal with a light wavelength that corresponds to a unique color. Due to the physical properties of light, channels cannot interfere with each other. All WDM wavelengths are therefore independent. The creation of these virtual optical channels reduces the number of fibers to a single one. New channels can be integrated as needed, without disrupting existing fiber optic services. Since each channel is transparent to the data rate and type, all SAN, WAN, voice, and video services can be mixed and transported simultaneously over a single fiber or fiber pair. WDM Multiplexers: This is the main equipment that optimizes channel utilization on a WDM optical infrastructure. The WDM multiplexer combines all data streams into different optical channels, multiplexes them, and transmits them for simultaneous transport over a single optical fiber. Originally, WDM systems were only capable of transporting two bidirectional channels over a pair of fibers. Technology has evolved rapidly, and both the number of channels and the amount of data per channel transported have increased. Today, up to 80 channels can be transmitted simultaneously over a fiber at any time. Typically positioned at the endpoints of a network, multiplexers are often referred to as "terminal multiplexers." When connecting two sites, a multiplexer is placed at each site to create a point-to-point connection. In many cases, networks have additional sites. Some sites are only concerned with a few services or channels, while others are intended for other data centers. When connectivity is required in some form, but not for all types of traffic, multiplexers (OADMs) must be added to extract the wavelengths desired and needed for the specific site while bypassing unnecessary traffic types. In this way, more versatile rings can be realized with more distribution possibilities. Patch cord - Transceiver – MUX The transceiver transmits high-speed data protocols over narrowband wavelengths, while the multiplexer receives these channels and consolidates them onto a single fiber. The patch cable; a cord with an LC connector; allows these two key elements to be brought together.

Dark Fiber: Fiber Pair or Single Fiber A prerequisite for any WDM solution is access to a dark fiber network. The most common way to transport traffic over an optical architecture is to use a fiber pair. One fiber is used for data transmission and the other is used for data reception. This allows for maximum traffic to be carried. Sometimes only one fiber is available. DWDM systems easily allow infrastructure to be built using one wavelength to send data and a second to receive.