Coarse Wavelength Division Multiplexing (CWDM) is the technique of combining several optical channels  onto a single fiber. CWDM technology uses an ITU standard 20nm spacing between the wavelengths, from 1310nm to 1610nm. With CWDM technology, since the wavelengths are relatively far apart (compared to DWDM), the transponders, lasers and filters are generally not very expensive. CWDM equipment is envisaged as a cost effective solution for Metro Access and Metro Core/Regional network environments where more emphasis is on  the network nodes at fairly short spans.