Why DWDM?

The Answer to Growing Data Demands & Network Expansion

When you need to move a lot of data over long distances, you’ll need DWDM products and technology. Those undersea fiber cables connecting all the world’s continents? Middle-mile networks that serve as the internet on-ramp for remote or rural communities? Connecting your warehouse/factory to your office across the state, or across the country? All DWDM.

Regardless of whether you are service provider or building your own optical network, Dense Wavelength Division Multiplexing (DWDM), is the foundation for transporting gigabit to terabit speeds over long distances.

DWDM: Invented To Increase Capacity

Before DWDM can be utilized, optical fiber infrastructure must exist between sites. Laying fiber cables is an expensive, capital-intensive undertaking that involves trenching, conduits, rights-of-way, and networking equipment operating in potentially harsh environments. For example, the Southern Cross Cable, with 3 fiber pairs between Sydney and Hawaii and 4 fiber pairs between Hawaii and the US West Coast, cost $1.5 billion to build in 2000. Nowadays, fiber is widely available and can be leased from a number of providers, further decreasing the cost to customers.

Increasing bandwidth and capacity to maximize fiber investments, is therefore of utmost importance. Before DWDM, one strand of fiber optics supported a single wavelength (color) of light, or a single channel. This is similar to copper cables, where a pair of copper wires only supports a single channel. However, fiber provides the medium to propagate light and not electricity. By using different wavelengths of light, a single fiber can support a wide range of channels. For reference, many Internet Service Providers utilize equipment that can comfortably support 100G or 400G data rates over a single channel.

Combining multiple channels at one end of the fiber (MUX) and splitting them back into separate channels at the other end (DEMUX) is called multiplexing. DWDM does this at the optical layer, not the packet layer. One wavelength may be carrying ethernet traffic between routers, whilst another carries Fiber Channel traffic between storage devices. For more complex network designs such as rings, meshes, and other topologies, Optical Add-Drop Multiplexers (OADM) were developed. Modern implementations of this technology are the FOADM (Fixed OADM) and ROADM (Reconfigurable OADM).

Wait, what About CWDM?

Coarse Wavelength Division Multiplexing (CWDM) was introduced in the early 1980s, over a decade before DWDM became commercially available. The concept of multiplexing wavelengths is the same for both. As its name implies, Coarse has wider channel spacing, resulting in significantly less channel support in total relative to Dense.

For CWDM, specifications are less stringent so lower cost lower performance optics can handle the job. However, optical amplifiers such as EDFAs (Erbium Doped Fiber Amplifier) do not work due to the coarse (i.e. wide) channel spacings of CWDM. This limits its reach and restricts CWDM to local, short range links.

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