CWDM operates in the wavelength range of 1270nm to 1610nm, with each CWDM channel typically separated by 20nm. There are a total of 18 CWDM channels – initial technology was developed for 9 (1470-1610) channels, and was later expanded to 18 channels that include lower wavelength channels with less effective attenuation.

CWDM (Coarse Wavelength Division Multiplexer) is a sparse wavelength division multiplexer, also known as a coarse wavelength division multiplexer. CWDM has 18 different wavelength channels, each with different wavelengths separated by 20 nm, using wavelengths from 1270 nm to 1610 nm.