What is the difference between 850nm, 1310nm, and 1550nm wavelengths?
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These three wavelengths represent the primary "windows" in fiber optic communications, each with distinct characteristics.
850nm — Short Wavelength
- Used with multi-mode fiber (MMF)
- Higher attenuation (~3.5 dB/km)
- Uses VCSEL lasers — cheap
- Modal dispersion limits distance
- Common in: SR (Short Reach) optics
- Typical distances: 100-500m
1310nm — First Window
- Used with single-mode fiber (SMF), also MMF
- Lower attenuation (~0.35 dB/km on SMF)
- Zero-dispersion wavelength for standard SMF
- Uses Fabry-Perot or DFB lasers
- Common in: LR (Long Reach) optics
- Typical distances: 2-10 km
1550nm — Second Window
- Used with single-mode fiber (SMF)
- Lowest attenuation (~0.25 dB/km)
- Best for very long distances
- Uses DFB or EML lasers
- C-band for DWDM (1530-1565nm)
- Common in: ER, ZR optics, DWDM
- Typical distances: 40-160+ km
- Requires more expensive components
Wavelength Comparison
| Wavelength | Attenuation (SMF) | Best Use |
|---|---|---|
| 850nm | Not used on SMF | Short MMF |
| 1310nm | 0.35 dB/km | Medium distance |
| 1550nm | 0.25 dB/km | Long distance |
| 1625nm | 0.25 dB/km | OTDR monitoring |
Special Bands
- O-band (1260-1360nm): Original, includes 1310nm
- E-band (1360-1460nm): Water peak region, avoided in older fiber
- S-band (1460-1530nm): Short wavelength
- C-band (1530-1565nm): Conventional, DWDM primary
- L-band (1565-1625nm): Long wavelength, DWDM expansion
Why Different Wavelengths?
- Match wavelength to fiber type
- Optimize for distance and cost
- Enable WDM (multiple wavelengths on one fiber)
- Physical properties of components (lasers, detectors)
2 Other Answers
16
C-band DWDM is the workhorse of long-haul optical. L-band adds capacity growth.
13
Understanding wavelengths is fundamental. Great overview.
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