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Both CWDM and DWDM multiply fiber capacity by putting multiple wavelengths on a single fiber pair. But the two technologies serve different reaches, different channel counts, and different budgets. Using DWDM where CWDM would suffice wastes money. Using CWDM where DWDM is required caps your capacity at launch. Here is how to get the call right.
CWDM (Coarse WDM) spaces wavelengths 20 nm apart across the 1270–1610 nm range, giving you up to 18 channels. The wide spacing means cheaper, uncooled lasers can be used — no temperature stabilization needed. Channel wavelength drifts a few nanometers? No problem.
DWDM (Dense WDM) packs wavelengths as close as 0.4 nm (50 GHz) or 0.8 nm (100 GHz) within the C-band (1530–1565 nm). This requires temperature-stabilized, precision-tuned lasers. The payoff: 40 to 96 channels on the same fiber pair — and compatibility with EDFA amplification, which only works in the C-band.
| Parameter | CWDM | DWDM |
|---|---|---|
| Channel spacing | 20 nm | 0.4–0.8 nm (50/100 GHz) |
| Max channels | 18 | 40–96 (C-band) |
| Wavelength range | 1270–1610 nm (O to L band) | 1530–1565 nm (C-band) |
| Laser type | Uncooled DFB (cheaper) | Cooled DFB / tunable (precise) |
| Amplification | Not compatible with EDFA | Fully EDFA-compatible |
| Max reach (unamplified) | ~80 km | ~80–120 km |
| Max reach (amplified) | N/A | 500+ km (with EDFA/Raman) |
| Transceiver cost | Lower | Higher |
| Best for | Sub-80 km, ≤18 channels | 80+ km, >18 channels, any amplification |
Here is the single most important rule: if your link needs amplification, you must use DWDM. EDFAs only amplify wavelengths in the C-band (and L-band variants). CWDM channels spread across the full 1270–1610 nm range — most of them fall outside the EDFA window and cannot be amplified. For any link over 80–100 km where the fiber loss exceeds your power budget, CWDM is not an option.
This also means: if you deploy CWDM today and later need to extend the link beyond 80 km, you cannot simply add an amplifier. You will need to replace the entire wavelength plan with DWDM — transceivers, MUX/DEMUX, everything.
A single CWDM fiber pair with 18 channels at 400G each gives you 7.2 Tbps — enough for most enterprise and mid-size colocation DCI links. At 800G per channel, that is 14.4 Tbps. For operators with modest growth projections and link distances under 80 km, CWDM is the right economic choice — lower transceiver cost, simpler deployment, no amplifier complexity.
The breakpoint: when you project needing more than 18 channels within the lifespan of the fiber plant, start with DWDM from day one. Retrofitting CWDM to DWDM means touching every active port on the link.
Decision heuristic: If your link is (a) under 80 km, (b) you need 18 or fewer channels, and (c) you have no plans to extend the distance — deploy CWDM. If any one of those three conditions is false — deploy DWDM. It costs 15–25% more upfront but avoids a full wavelength re-deployment.
APEX Group supplies both CWDM and DWDM transceivers across 25G to 800G form factors, paired with matching passive MUX/DEMUX units. For links that start CWDM and grow into DWDM, the same procurement relationship supports both technologies — a single partner across the wavelength plan, however it evolves.
APEX GROUP — www.apexallinone.com
