CWDM vs DWDM: Channel Spacing, Reach, and Where Each Wins

The two ITU grids

• CWDM (ITU-T G.694.2) — 20 nm spacing between channels, 1271–1611 nm

total band. Up to 18 channels in practice (some bands trimmed by water peak). Wide spacing means cheap, uncooled DFB lasers.

• DWDM (ITU-T G.694.1) — 100 GHz (0.8 nm) or 200 GHz spacing on the

C-band grid around 1550 nm. Up to 80+ channels at 50 GHz spacing. Requires temperature-stabilized lasers and tight filter passbands.

Reach and amplification

Because DWDM channels sit in the C-band, erbium-doped fiber amplifiers (EDFAs) can boost the whole comb at once — reaches of hundreds of kilometers are routine in long-haul. CWDM's wide band excludes EDFA-only operation; you amplify per channel or terminate at every site.

Cost and operational complexity

Decision rule

• Need ≤ 8 channels, ≤ 80 km, low capex? → CWDM (1U rackmount or LGX).

• Need > 16 channels, long-haul, or 100 G+ per channel? → DWDM with

coherent 100 G/400 G ZR transceivers.

• Metro at 8–16 channels, < 80 km? → 200 GHz DWDM offers better

reach-density than CWDM at a modest cost premium.

Shop our CWDM and DWDM modules or talk to sales about custom channel maps.