What is CWDM and DWDM - understanding wavelength division multiplexing?
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WDM (Wavelength Division Multiplexing) transmits multiple channels on a single fiber using different wavelengths. CWDM and DWDM differ in channel spacing.
CWDM (Coarse WDM)
- Wide channel spacing: 20nm (2500 GHz)
- 18 channels typical (1271-1611nm, ITU G.694.2)
- Uncooled lasers — lower cost
- Passive multiplexers/demultiplexers
- Distances: typically 40-80km
- Cost-effective for medium capacity
DWDM (Dense WDM)
- Narrow channel spacing: 100 GHz, 50 GHz, or 25 GHz
- 40, 80, 160+ channels possible
- C-band (1530-1565nm) most common
- Cooled lasers — precise wavelength
- Amplification with EDFAs possible
- Distances: 100km to 1000+ km
- Higher cost, higher capacity
Comparison Table
| Feature | CWDM | DWDM |
|---|---|---|
| Spacing | 20 nm | 0.4-0.8 nm |
| Channels | Up to 18 | 40-160 |
| Distance | 40-80 km | 100-1000+ km |
| Cost per channel | Lower | Higher |
| Amplification | Limited | EDFA supported |
| Typical use | Metro, campus | Long-haul, DCI |
When to Use CWDM
- Campus/metro networks <80km
- Limited fiber pairs available
- Moderate capacity needs (up to 18 wavelengths)
- Budget-conscious deployments
When to Use DWDM
- Long-haul transmission >80km
- Very high capacity requirements
- Data center interconnect (DCI)
- Service provider backbone
- Growth capability to hundreds of channels
Colored Optics
SFP+ and QSFP28 modules are available as "CWDM colored" or "DWDM tunable" — plug directly into standard switches without external transponders.
2 Other Answers
19
Tunable DWDM SFPs eliminated our transponder shelf. Massive space and power savings.
13
For metro rings up to 80km, CWDM hits the sweet spot on cost/capacity.
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