CWDM(Coarse Wavelength Division Multiplexing) VS DWDM(Dense Wavelength Division

WDM(Wavelength Division Multiplexing) technology offers a cost-effective solution to increase network capacity without deploying additional optical fiber in your existing fiber optic network. CWDM and DWDM are two main WDM technologies with different wavelength patterns, capabilities, costs, and applications. 

CWDM stands for Coarse Wavelength Division Multiplexing, and the term “Coarse” refers to the wavelength spacing between channels. CWDM has a wider channel spacing of 20nm, and it is standardized to have 18 different wavelength channels with a spacing of 20 nanometers (nm) starting at 1270 nm and ending at 1610 nm. Most systems use the eight channels in the upper band (eight channels from 1470 nm to 1610 nm). The official ITU grid refines the wavelength of CWDM is 1471, 1491, 1511, etc., although the common commercial reference of 1470, 1490, 1510, etc. Its bands cover O, E, S, C, and L five bands of single-mode optical fiber system. And 1310nm and 1550nm are two most commonly two wavelength regions, 1550nm region is more popular because it has a lower loss in the fiber.
 
The optical spacing enables CWDM to transmit and receive up to 18 channels over a fiber pair. The larger spacing also means that the structure of the optical combiner and demultiplexer is greatly simplified, and the number of coating layers of the filter is reduced. As a result, yields are increased and costs are reduced.
 
DWDM is Dense Wavelength Division Multiplexing, and its wavelengths are located within the narrow 1525nm to 1565nm region known as the C-Band, and being expanded into the 1570-1610nm L-Band spectrum. DWDM has a wavelength spacing of 0.4nm(50GHz), 0.8nm(100GHz), or 1.6nm(200GHz). Due to its narrow wavelength spacing, DWDM carries 40, 80, 96 or up to 160 wavelengths by utilizing a much narrower spacing.

CWDM VS DWDM
CWDM is usually used for lower cost, lower capacity (sub-10G) and shorter distance applications where cost is an important factor. Since CWDM is based on 20nm channel spacing from 1470 to 1610 nm, it's typically deployed on fiber spans up to 80km or less because optical amplifiers cannot be used with large spacing channels.
 
DWDM spaced at 0.8nm spacing that it can transmit a huge quantity of data through a single fiber link as they allow for many more wavelengths to be packed onto the same fiber. Unlike CWDM, DWDM connections can be amplified and can, therefore, be used for transmitting data much longer distances. DWDM is optimal for long-reach communications up to hundreds or thousands of kilometers.
 
CWDM is used in: Metropolitan area network access layer, telecommunications, enterprise network, campus network, etc. DWDM is suitable for: long-distance, high-capacity long-distance trunk network, or ultra-large-capacity metropolitan area network core node.