What is DWDM and when should you use it?

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What is DWDM?

DWDM stands for Dense Wavelength Division Multiplexing, a fiber optics technology for connecting multiple channels over a dark fiber pair using a multiplexer. By transmitting each channel on a different wavelength, DWDM maximizes fiber usage and helps organizations meet growing capacity demands without laying or leasing additional fiber until it is necessary.

DWDM at a glance

How do you choose DWDM channel spacing?

DWDM channel spacing affects both how many wavelengths a line system can carry and the capacity available on each wavelength. The channels are concentrated in the low-loss region around 1550 nm. Narrower channel spacing fits more wavelengths into the available spectrum, but you often need wider channels to accommodate higher-capacity signals such as 400G and 800G.

*Smartoptics coherent QSFP-DD transceivers provide a unique solution, supporting 200G over existing 50 GHz filters.

Channel spacing is also an upgrade decision. The filters in a fixed-grid system determine the spectral width available to future signals, so a network designed around 50 or 100 GHz channels can limit which higher-capacity optics can be added later. FlexGrid removes that fixed channel structure by allocating spectrum according to each signal, giving the optical layer more room to evolve.

CWDM vs. DWDM

Both dense WDM (DWDM) and coarse WDM (CWDM) can transmit a mix of data, storage, voice or video traffic on multiple wavelength channels over a single dark fiber. Collectively, CWDM and DWDM are commonly referred to as xWDM.

The main difference is how the channels are spaced along the optical spectrum. CWDM wavelengths are 20 nm apart and support up to 18 channels. DWDM channels are spaced much more closely, allowing substantially greater wavelength density. DWDM signals can also be amplified, making the technology suitable for higher-capacity transport over longer distances.

DWDM is the standard choice for new WDM networks, as CWDM remains mostly in legacy deployments. DWDM supports much greater capacity, higher line rates and longer reach than CWDM. DWDM is also comparably affordable, removing the traditional cost advantage of CWDM.

Passive vs. active DWDM

DWDM can be deployed as a passive or active system. Passive DWDM is used for cost-efficiency in shorter and less-demanding links, such as point-to-point 16G. However, the amplification and dispersion compensation of active systems are increasingly necessary for supporting higher bit rates at longer distances.

In a passive, unpowered solution, the DWDM transceiver resides directly in the data switch or router. Its output connects to an unpowered multiplexer that combines and separates the different wavelength channels. In this architecture, the DWDM functionality is embedded in the network equipment and passive optical components.

Active DWDM solutions add powered optical transport equipment such as line systems and transponders or muxponders. The line system can provide functions that enhance reach, stability and performance such as amplification, monitoring and dispersion compensation. Transponders use optical-electrical-optical (OEO) conversion to translate short-range client signals into DWDM line signals when DWDM optics cannot be embedded directly in the switch or router, and can also provide a demarcation point for signal hand-off and monitoring.

The latest open line system technology provides the benefits of an active system with the ease of use of a traditional passive system.

When should you use DWDM?

DWDM is especially valuable when the limitation is no longer the speed of one connection, but how much useful capacity can be extracted from the available fiber infrastructure.

When fiber is scarce or expensive. Without DWDM, adding more connections can mean adding or leasing more fiber. DWDM lets multiple services share the same fiber pair, making much better use of the fiber already available.

When capacity is growing. DWDM requires more optical infrastructure upfront, but the economics improve quickly as more services are added. Instead of fiber costs rising with every new connection, additional capacity can be added as wavelengths over the same fiber pair.

When reach goes beyond a simple local link. Unamplified DWDM commonly supports links up to around 80 km. With coherent optics and amplification, DWDM can extend across regional and long-haulf networks into hundreds or even more than 1,000 km with ZR++.

Open DWDM and open line systems

Traditional optical networking solutions often combine optics, transponders, line-system functions and management in a tightly integrated monolithic system. Open DWDM separates these functions so you can choose the mix that best fits your network. At the center of this architecture is an open line system that provides a common optical layer for combining and transporting wavelengths from different sources.

This means coherent DWDM transceivers can be embedded directly in routers or switches for IP over DWDM, while transponders and muxponders can be added to the same open line system where they make sense. You can combine interoperable network elements from different vendors rather than tying the optical layer to one vertically integrated solution, and grow your network across different services, line rates and equipment generations.

Build your DWDM network with Smartoptics

The Smartoptics optical networking portfolio combines open line systems, optical transceivers, transponders and muxponders with optical networking expertise for DWDM networks ranging from point-to-point links to regional ROADM architectures. Compact 1RU systems, plug-and-play deployment, low power consumption and no hidden license fees help keep both costs and operational complexity down.

For a broader introduction to wavelength division multiplexing and the components used to build WDM networks, download the What is WDM? guide.