Coarse wavelength division multiplexing (CWDM) is a very high cost performance increase the bandwidth capacity of technical solution, based on 1 ru. 19 "rack mount case of wavelength division wave module is easy to install and modular assembly. The system can provide network equipment manufacturers more scalability and high density solution. The WDM system is suitable for application in the PDH, SDH/SONET and Ethernet business, in the field of metropolitan area optical network and access network application is very extensive.