WDM or Wave Division Multiplexing knows two international standards, one of them is CWDM, Coarse Wave Division Multiplexing. Coarse indicates a larger space between the waves or, as they are commonly referred to, channels. CWDM is often used in situations where only a few channels are needed and there is no need for distances longer than 70 km. Opticonnect offers a range of Passive CWDM Multiplexers using channels between 1270 nm an1610 nm with a channel spacing of 20 nm.
Passive CWDM is an implementation of CWDM that uses no electrical power. It separates the wavelengths using passive optical components.