CWDM channel plan

The CWDM grid (ITU-T G.694.2) defines 18 wavelengths spaced 20 nm apart, from 1271 nm to 1611 nm. Each is a channel a coloured transceiver can occupy.

The 18 wavelengths (nm)

1271  1291  1311  1331  1351  1371  1391  1411
1431  1451  1471  1491  1511  1531  1551  1571
1591  1611

What gets used in practice

• The eight wavelengths 1471–1611 nm are the most common, because they sit away

from the fibre's high-loss "water peak" region around 1383 nm and outside the O-band used by other services.

• Systems are sold as 4-, 8- or up to 18-channel muxes.

Colours

Each wavelength has a conventional colour so field engineers can match a transceiver to its mux port by sight. The module still reports its exact wavelength in memory.

In CodingBox the wavelength field appears on the Check transceiver screen — a quick way to verify a coloured CWDM module without reading the label.