Coarse wavelength division multiplexing (CWDM): CWDM refers to WDM systems with fewer than eight active wavelengths per fiber. CWDM is used for short-range communications. WDM systems are divided into three different wavelength patterns: normal (WDM), coarse (CWDM) and dense (DWDM). CWDM solutions are available in industry-standard 20 nm spacing with options for a 1310 nm RF overlay bypass as well as single or bidirectional test ports.