Difference between CWDM and DWDM networks
Wavelength-division multiplexing (WDM) has become increasingly popular in fiber-optics communications as it allows transmission of multiple signals onto a single optical fiber. WDM enables bidirectional (BiDi) communication over one strand of fiber by sending signals utilizing different wavelengths that can be spaced apart. WDM systems are very popular in the telecommunication industry because it allows networks to expand their capacity without laying more fiber. In addition, the capacity of a link can also be expanded by upgrading the multiplexers and demultiplexers at each end of a link. Currently there are two common types of WDM technology, CDWM and DWDM. CWDM (coarse wavelength division multiplexing) and DWDM (dense wavelength division multiplexing) are based on the same concept but differ in a number of areas such as spacing of the wavelengths, number of channels, transmission distance, power requirements, and price.
Wavelength Spacing & Number of Channels
One of the key differences of CWDM versus DWDM is the spacing that each uses to separate the signals they carry. CWDM provides up to 18 channels with different wavelengths, each channel is spaced exactly 20nm apart. CWDM technology features a much wider channel spacing than DWDM. DWDM technology is capable of 40, 80, or up to 160 wavelength channels with a spacing of 0.8/0.4nm apart.
DWDM technology is capable of transmitting long haul distances by keeping wavelengths tightly packed. CDWM systems are capable of transmitting at a distance of up to 160km (100 miles). CWDM’s distance limitation is due to the fact that the wavelengths it carries are not amplified. DWDM connections however can be amplified thus it is able to span much longer distances.
CWDM systems use an uncooled distributed-feedback laser while DWDM systems use a cooled distributed-feedback laser. The difference between having a cooled versus uncooled laser means that DWDM consumes much more power than its uncooled counterpart (CWDM). The coolers along with auxiliary components consume approximately 4W per wavelengths while an uncooled laser consumes about 0.5W of power. Although it requires more power, cooling lasers which adapt temperature tuning aids in ensuring better performance, better safety, and a longer lifespan for DWDM systems.
DWDM system prices are commonly four or five times higher than CWDM systems. The higher cost of DWDM can be attributed to the fact that it requires cooled temperature-controlled lasers. The manufacturing wavelength tolerances for DWDM lasers are also a key factor, DWDM laser tolerances are ±0.1 nm, while tolerances for CWDM laser die are ±2-3 nm. Lower die yields lead to higher costs for DWDM lasers.