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Dense Wavelength Division Multiplexing or DWDM is one of the two methods used for wavelength division multiplexing in fiber optic communications, the other being coarse wavelength division multiplexing or CWDM. Wavelength division multiplexing is a technique which multiplexes several optical signals onto a fiber optic cable by using different wavelengths of the light.

Comparison of DWDM and CWDM Systems

Both CWDM and DWDM provide higher bandwidth by consuming lesser number of cores of fiber optic cable and fewer ports of communication equipment. The higher bandwidth is a result of transmitting multiple streams of data on a single fiber at the same time. All of the channels being transmitted accumulate to a consolidated bandwidth which is much higher than the normal data transmission methods which use single transmit and receive channels.

CWDM and DWDM use similar techniques for data transmission, the major difference being the channel spacing. In CWDM the channel spacing is wider than the DWDM. As the name suggest, the number of channels in DWDM are much denser than that of CWDM. The more the channels, the more the bandwidth.

DWDM transceivers today are primarily available as SFP, XFP and SFP+ form-factors providing 1 Gbps and 10 Gbps bandwidths respectively. The channel spacing is denser in SFP+ DWDM transceivers as compared to SFP DWDM transceivers. DWDM has the capability to carry 40 Gbps, 100 Gbps and 400 Gbps data in a single core of fiber optic cable. DWDM transceivers require very delicate technology and accurate wavelength splitting as the channel spacing is very small. This results in the DWDM transceivers to be higher in cost than the CWDM transceivers.

Operating Principle of DWDM Systems

DWDM systems make use of the 1525–1565 nm wavelength band, this range of wavelengths is often referred to as C-band. Other wavelength range that is frequently used is the L-band which refers to 1570–1610nm wavelengths. The channels spacing in DWDM systems is exactly 100 GHz which corresponds to 0.8 nm of wavelength spacing. Using the above mentioned channel spacing, 50 channels can be squeezed in to any band. Recently, more precise DWDM transceivers have been introduced, which reduce the channel spacing to 50 GHz. Transceivers having 25 GHz channel spacing have also been introduced, effectively increasing the channel count to 200 channels per fiber optic core.


DWDM systems provide extreme high bandwidths over a longer distance. This is made possible by utilizing the full spectrum of laser light and sending multiple streams of data over it. DWDM systems can also be utilized to send different types of data over different wavelengths of light. If the up-front cost of implementation is not an issue, DWDM systems can be installed to make full use of the network infrastructure’s speed and reliability.