An optical multiplexing technique specified by the ITU-T as 18 wavelengths in the 1270
(Course WDM) An optical transmission method that is used for shorter distances than dense WDM (DWDM). Also known as "wide WDM," CWDM transmits fewer channels and uses wider spacing between the channels for distances up to 60 km. Wider spacing up to 25 nm, compared to 1.6nm and smaller for DWDM, tolerates more temperature fluctuation. Standardized by the IEEE in 2004 for 10 Gigabit Ethernet, CWDM components are much less costly than DWDM because the laser does not have to be stabilized, and an external modulator is not required. The laser can be modulated directly by changing the drive current. CWDM operates between 1265 and 1625 nm compared to DWDM's tighter 1530-1620 range. See WDM.