Single-mode fiber typically exhibits an attenuation of about 0.22 dB/km at 1550 nm and 0.38 dB/km at 1310 nm.

Typical Attenuation Values

For a 1 km length of single-mode fiber, the expected signal loss depends on the operating wavelength:

• 1550 nm (preferred for long-haul links): ~0.22 dB/km under normal conditions, with ideal fibers reaching ~0.17–0.18 dB/km .
• 1310 nm (zero-dispersion region): ~0.38 dB/km under normal conditions, with ideal fibers around 0.3–0.35 dB/km . This means that over 1 km, a signal would lose roughly 0.22 dB at 1550 nm or 0.38 dB at 1310 nm, excluding additional losses from connectors, splices, or bends.

Factors Affecting Attenuation

1. Intrinsic Losses:
   • Rayleigh scattering: Caused by microscopic density variations in the glass, stronger at shorter wavelengths.
   • Absorption: Energy from light is absorbed by the glass material, converting it to heat .
2. Extrinsic Losses:
   • Bending and stress: Macro-bends or tight routing can increase loss.
   • Splices and connectors: Typical fusion splices add 0.05–0.2 dB each, while connectors can add 0.2–0.5 dB per connection .
3. Environmental Factors:
   • Temperature variations, dust, and repeated connector mating can slightly increase attenuation over time .

Practical Considerations

• 1550 nm is preferred for long-distance transmission because it has roughly 40% lower attenuation than 1310 nm, allowing signals to travel farther before requiring amplification or regeneration .
• ITU-T G.652 standard specifies single-mode fiber characteristics, including attenuation coefficients, ensuring compatibility and predictable performance for both 1310 nm and 1550 nm regions .
• For network design, it is common to include a margin of 2–6 dB to account for aging, splices, connectors, and environmental effects . In summary, for a 1 km run of modern single-mode fiber, expect 0.22 dB loss at 1550 nm and 0.38 dB loss at 1310 nm, with additional minor losses from connectors, splices, and bends. Proper installation and handling can minimize extrinsic losses and maintain signal integrity.