The CWDM wavelength grid covers 18 nominal center wavelengths from 1271 to 1611 nm, spaced 20 nm apart under ITU-T G.694.2. Many conventional CWDM links use the eight higher-wavelength channels, from 1471 through 1611 nm, because they avoid the water-peak region that can cause high attenuation on older single-mode fiber.<\/p>\n\n\n\n
That’s the short answer. The chart below is the longer one, and it addresses a question that frequently comes up during channel planning: is the first channel 1270 or 1271 nm?<\/p>\n\n\n\n
Both numbers appear in industry documentation. Neither is necessarily a typo.<\/p>\n\n\n\n
Consider an illustrative case: Priya, a transport engineer at a regional ISP, is preparing an overnight cutover. Her eight-channel span comes up with six channels carrying traffic, while the 1371 and 1391 nm channels remain down. The installed fiber turns out to be G.652.B rather than the low-water-peak fiber shown in the as-built drawings.<\/p>\n\n\n\n
The optics may be functioning correctly; the unverified fiber attenuation at those wavelengths could be enough to exceed the link budget.<\/p>\n\n\n\n
This page is a wavelength chart, not another general CWDM explainer. It covers all 18 wavelengths, their optical bands and fiber considerations, the color-code convention and its limits, four ready-made channel plans, and the wavelength-tolerance considerations behind 20 nm spacing. For the fundamentals, start with our complete CWDM guide<\/u><\/a>.<\/p>\n\n\n\n Key Takeaways<\/strong><\/p>\n\n\n\n\n