WDM can be subdivided into CWDM (Sparse Wavelength Division Multiplexing) and DWDM (Dense Wavelength Division Multiplexing). The channel interval of CWDM is 20nm, and the channel interval of DWDM is from 0.2nm to 1.2nm, so relative to DWDM, CWDM is called sparse wavelength division multiplexing technology.

DWDM is dense wavelength division multiplexing, with dense band spacing (0.4nm or 0.8nm), a large number of channels, and high technical requirements. It is mainly used on trunk lines, but also in local networks and metropolitan area networks. High single-channel transmission rate and large system capacity