Attenuation per kilometer of single-mode optical fiber

The typical attenuation loss of single-mode optical fiber is about 0.35 dB/km at 1310 nm and 0.20 dB/km at 1550 nm.

Overview of Attenuation

Attenuation in optical fiber is the reduction of optical power as light travels through the fiber. It is primarily caused by absorption and scattering. Absorption occurs when light energy is converted to heat by molecules in the glass, with residual OH⁺ ions and dopants being the main contributors. Scattering, particularly Rayleigh scattering, occurs when light interacts with microscopic variations in the glass and is inversely proportional to the fourth power of the wavelength, meaning longer wavelengths experience lower scattering losses .

Typical Loss Values

For modern single-mode fibers:

• At 1310 nm: Attenuation is typically 0.30–0.40 dB/km, often rounded to 0.35 dB/km for planning purposes .
• At 1550 nm: Attenuation is lower, around 0.18–0.25 dB/km, commonly taken as 0.20 dB/km . These values represent the intrinsic fiber loss and do not include additional losses from connectors, splices, or bends.

Factors Affecting Attenuation

1. Wavelength: Longer wavelengths reduce scattering losses, which is why 1550 nm is preferred for long-distance transmission .
2. Fiber Quality: Impurities, dopants, and manufacturing defects can increase absorption and scattering.
3. Installation Factors: Bends, splices, and connectors introduce extra losses. Typical connector loss is 0.2–0.75 dB, and fusion splices add 0.05–0.2 dB each .
4. Environmental Conditions: Temperature changes and mechanical stress can slightly affect attenuation.

Practical Implications

For a 1 km run of single-mode fiber, the expected intrinsic loss is:

• 1310 nm: ~0.35 dB
• 1550 nm: ~0.20 dB When designing a fiber optic link, these values are used in the link budget to ensure sufficient signal power reaches the receiver, accounting for additional losses from connectors, splices, and system margin . Using the longer wavelength (1550 nm) is advantageous for minimizing attenuation and maximizing transmission distance between repeaters or amplifiers.