DWDM refers to Dense Wavelength Division Multiplexing. The technology supports multiplexed transmission of multiple optical wavelengths in a single fiber strand. Similar to CWDM, DWDM is also a form of WDM technology. However, by defining smaller wavelength spacing, it can provide the maximum number of channels, and therefore has a greater overall capacity. Hence, Dense Wavelength Division Multiplexing can rapidly increase the bandwidth capacity of existing fiber networks.
In other words, DWDM creates multiple virtual optical fibers, increasing bandwidth on existing fiber optic backbones. More specifically, the technique multiplexes the tight spectral spacing of a single fiber carrier in a given fiber to take advantage of the achievable transmission performance (e.g., with minimal dispersion or attenuation).