CWDM overview

Coarse Wavelength-Division Multiplexing (CWDM) carries several independent channels on one fibre by giving each its own wavelength, spaced widely apart. It is a cost-effective way to multiply capacity without laying more fibre.

The idea

• Each channel uses a different wavelength (a "colour").
• A passive multiplexer combines them onto one fibre; a demultiplexer splits them at the far end. No power is needed for the mux itself.
• The wide 20 nm spacing (ITU-T G.694.2) lets modules use uncooled lasers, which keeps CWDM optics simple and inexpensive.

Trade-offs

• Simple and cheap — no laser cooling, passive mux.
• No amplification — most CWDM wavelengths fall outside the EDFA band, so CWDM is used mainly for shorter metro and access links rather than long haul.

Modules

CWDM transceivers are colour-coded by wavelength (a coloured SFP/SFP+ per channel). The exact set of wavelengths is the channel plan.

CodingBox reads a module's wavelength from its memory, so you can confirm a coloured module is the channel you expect before installing it.

Further reading

• Single-fibre CWDM, OADMs & band splitters — paired wavelengths on one strand, add/drop losses, bus and ring topologies, a worked add/drop budget.
• CWDM in access & mobile fronthaul — CPRI/eCPRI, CWDM 6/12/18, MWDM and LWDM plans, industrial-temperature requirements, semi-active WDM.