Coarse wavelength division multiplexing (CWDM) is a wavelength division multiplexing (WDM) technology that combines multiple signals at various wavelengths for simultaneous transmission over fiber cables. This passive technology allows for any protocol to be transported over the link, as long as it is at a specific wavelength (i.e. T1 over fiber at 1570nm transported alongside 10Gbps Ethernet at 1590nm).
CWDM is a low-cost method to maximize existing fiber by decreasing the channel spacing between wavelengths. CWDM has a lower cost per channel than dense WDM (DWDM) and no configuration is necessary.