CWDM is mainly used in passive wavelength division multiplexing module. It is a kind of wavelength division multiplexing technology based on TFF (thin film filter). It has a variety of package sizes and wavelength options. It consists of three ports: COM, Pass and Reflect. The wavelength range meets the ITU-I G.695 standard. It can multiplex, demultiplex or add-drop multiplexing different light in WDM system, as well as increasing signal transmission speed and communication capacity. CWDM is widely used in telecommunications, radio and television, enterprise network, campus network and other fields.