As today’s voice, video and data networks are requiring more bandwidths and faster data transmission rates over farther distances, IT managers are relying on more and more fiber optics. But the reality that many Service Providers and Enterprise Corporations are facing is that once their available fiber infrastructure is exhausted, laying more fibers is no longer an economical or feasible option. So they are turning to wave division multiplexing (WDM) technology.
WDM is a technology which can multiplex multiple optical signals on a single fiber by using different wavelengths, colors, of laser light to carry different signals. By using bidirectional communications over a single fiber, network managers can realize a multiplication effect in their available fiber’s capacity. Generally, WDM system can be divided into CWDM (coarse wavelength division multiplexing) and DWDM (dense wavelength division multiplexing). Both of them are indispensable technologies to increase capacity on the fiber links that are already in place. However, there are many differences between them. The following part will compare CWDM and DWDM mainly from four aspects, including wavelength spacing, power consumption, transmission distance and cost. The image below shows the working principle of WDM technology.
The space between two individual wavelengths transmitted through the same fiber is the basis for differentiating the CWDM and DWDM. CWDM has a wider channel spacing than DWDM, which can carry up to 16 channels on a single fiber in the spectrum grid from 1270 nm to 1610 nm with a 20 nm channel spacing. DWDM typically has the capability to transport 80, or up to 160 channels from the wavelengths of 1525 nm to 1565 nm (C-band) or 1570 nm to 1610 nm (L-band) with a narrower channel spacing of 0.8 nm. Therefore, the denser spacing allows DWDM have a higher performance for transmitting more optical signals on the same fiber than CWDM. The following picture shows the different wavelength spacing between CWDM and DWDM.
CWDM takes the advantage of lower power consumption, since it is based on uncooled distributed-feed-back lasers and wide-band optical filters, while DWDM deploys cooled distributed-feedback. For example, DWDM with cooled laser can consume around 4 w per wavelength, while CWDM with uncooled laser only consumes about 0.5 w per wavelength.
Another major difference between them is the transmission distance. DWDM is designed for longer haul transmission, while the CWDM is more suitable for shorter distance transmission, since its wavelengths are not amplified. Generally, CWDM can achieve the length link of up to 160 km, while an amplified DWDM system can go much further as the signal strength is boosted periodically throughout the run. So, if there is a need to transmit the data over a very long range, the DWDM will likely be the priority in terms of functionality of the data transmittal as well as the lessened interference over the longer distances that the wavelengths must travel.
As we have mentioned above, DWDM with cooled laser adopts temperature tuning, while the DWDM with uncooled laser uses electronic tuning. The range of temperature distribution is non-uniform in a very wide wavelength, so the temperature tuning is very difficult to realize, which results in high cost. Typically, a DWDM product is four or five time more expensive than CWDM counterpart. For example, a CWDM SFP only costs 45 dollars, while a DWDM SFP will cost 200 dollars.
CWDM and DWDM with different features are both important types of WDM architecture. CWDM is cheaper and has lower power consumption, but its performance is far behind DWDM. With the benefits and drawbacks of each system, users should think twice before choosing them. Whether to choose CWDM or DWDM depends on the number of channels you need and the cost associated with deploying each system you can afford.