From: Ena on
Coarse wavelength division multiplexing (CWDM) is a method of combining
multiple signals on laser beams at various wavelengths for transmission
along fiber optic cables, such that the number of channels is fewer than
in dense wavelength division multiplexing (DWDM) but more than in standard
wavelength division multiplexing (WDM).

CWDM systems have channels at wavelengths spaced 20 nanometers (nm) apart,
compared with 0.4 nm spacing for DWDM. This allows the use of low-cost,
uncooled lasers for CWDM. In a typical CWDM system, laser emissions occur
on eight channels at eight defined wavelengths: 1610 nm, 1590 nm, 1570 nm,
1550 nm, 1530 nm, 1510 nm, 1490 nm, and 1470 nm. But up to 18 different
channels are allowed, with wavelengths ranging down to 1270 nm.

The energy from the lasers in a CWDM system is spread out over a larger
range of wavelengths than is the energy from the lasers in a DWDM system.
The tolerance (extent of wavelength imprecision or variability) in a CWDM
laser is up to ± 3 nm, whereas in a DWDM laser the tolerance is much
tighter. Because of the use of lasers with lower precision, a CWDM system
is less expensive and consumes less power than a DWDM system. However, the
maximum realizable distance between nodes is smaller with CWDM.

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