There are several differences between DWDM and CWDM systems. CWDM systems are older and cannot fit as many data streams. CWDM systems, however, are also less expensive from the outset. The design, function and purpose also differ in terms of transmission length and distance.
When dealing with fiber optic transmission systems, there are two main types of wavelength division multiplexing, or WDM, systems used to transmit the necessary data: DWDM and CWDM. Coarse wavelength division multiplexing systems, or CWDM systems, are used when there are eight or fewer wavelengths in each fiber that are active. Dense wavelength division multiplexing systems, or DWDM systems, are used when there are eight or greater wavelengths active in each fiber.
Dense wavelength division multiplying systems can fit more than 40 different data streams in the same amount of fiber used for two data streams in a CWDM system. CWDM systems were invented prior to dense wavelength systems, because the cost of cabling was a major factor. Now that cabling and transmittal has become more affordable, DWDM systems are often used in place of CWDM systems. One other major difference is that wavelength systems define CWDM systems, while DWDM systems are defined by frequencies.
CWDM systems can perform many of the same tasks as a dense wavelength system, at a lesser initial cost. Despite the lower transmittal of data through a CWDM system, these are still viable options for fiber optic data transmittal. CWDM systems carry less data, but the cabling used to run them is less expensive and less complex. A DWDM system has much denser cabling and can carry a significantly larger amount of data, but it can be cost prohibitive, especially where there is a need for a large amount of cabling in an application.
Another major difference between the two is that DWDM multiplexing systems are made for longer haul transmittal, by keeping the wavelengths tightly packed. They can transmit more data over a significantly larger run of cable with less interference than a comparable CWDM system. If the need is there to transmit the data over a very long range, the dense system solution will likely be the best in terms of functionality of the data transmittal as well as the lessened interference over the longer distances that the wavelengths must travel.
CWDM cannot travel long distances because the wavelengths are not amplified, and therefore CWDM is limited in its functionality over longer distances. Typically, CWDM can travel anywhere up to about 100 miles (160 km), while an amplified dense wavelength system can go much further as the signal strength is boosted periodically throughout the run. As a result of the additional cost required to provide signal amplification, the CWDM solution is best for short runs that do not have mission critical data.