Dense Wavelength division multiplexing (DWDM) is a technology used to combine or retrieve two or more optical signals of different optical center wavelengths or frequencies in a fiber. This allows fiber capacity to be expanded in the frequency domain from one channel to greater than 100 channels. This is accomplished by first converting standard, non-DWDM optical signals to signals with unique WDM wavelengths or frequencies that will correspond to the available channel center wavelengths in the WDM multiplexer and demultiplexer. Typically, this is done by replacing non-WDM transceivers with the proper WDM channel transceivers. WDM channels are defined and labeled by their center wavelength or frequency and channel spacing. The WDM channel assignment process is an industry standard defined in International Telecommunications Union (ITU-T). Then different WDM signal wavelengths are combined over one fiber by the WDM multiplexer. In the fiber, the individual signals propagate with minimal interaction assuming low signal power. For high powers, multiple interactions can occur. Once the signals reach the fiber link end, the WDM demultiplexer separates the signals by their wavelengths, back to individual fibers that are connected to their respective equipment receivers. Optical receivers have a broad reception spectrum, which includes all of C band. Many receivers can also receive signals with wavelengths down to O band.
