The intrinsic loss of modern optical fiber is typically between 0.1 dB/km and 0.5 dB/km, depending on fiber type and wavelength.

Intrinsic Fiber Loss

The loss of the optical cable itself, also called intrinsic attenuation, is caused by the fiber material and structure rather than external factors like connectors or splices. The main contributors are:

• Material absorption: Light is absorbed by the fiber material, including impurities and water molecules trapped in the glass, which can absorb light at specific wavelengths such as 1300 nm and 2.94 µm .
• Scattering: Rayleigh scattering occurs due to microscopic variations in the fiber core, causing light to scatter and reduce transmitted power .
• Dispersion: While primarily affecting signal quality rather than power, dispersion can contribute to effective loss over long distances .

Typical Attenuation Values

• Single-mode fiber (SMF): High-quality SMF typically has 0.2–0.5 dB/km at 1310 nm and 0.15–0.3 dB/km at 1550 nm .
• Multimode fiber (MMF): Attenuation is higher, usually 0.5–3 dB/km depending on core size and wavelength .
• Specialty fibers: Mid-infrared fibers made from fluoride glasses (e.g., ZrF₄, InF₃) have lower losses at longer wavelengths compared to silica fibers .

Practical Implications

For a typical 10 km single-mode fiber link at 1310 nm, the intrinsic fiber loss would be approximately 2–5 dB, excluding connectors, splices, or other network components . This intrinsic loss is relatively small, which allows optical signals to travel long distances without amplification. Proper handling, avoiding tight bends, and using high-quality fiber ensures that intrinsic losses remain minimal . In summary, the optical cable itself contributes a small but measurable loss, usually expressed in dB per kilometer, and modern fibers are engineered to minimize this intrinsic attenuation for efficient long-distance transmission .