Wavelength-Dependent Attenuation
Fiber loss versus wavelength from Rayleigh scattering, the infrared and ultraviolet absorption tails and the OH water peak, and the loss of a span at your wavelength.
Attenuation at 1550 nm
0.187 dB/km
9.37 dB over 50 km
Breakdown
79 % Rayleigh
IR 0.0204, UV 0.0198, OH 0.0000 dB/km
Minimum Loss
1551 nm
0.187 dB/km (scattering meets the IR tail)
Windows
0.323 / 0.187
dB/km at 1310 / 1550 nm; 0.311 at the 1383 nm water peak
Attenuation Spectrum
Model
α = A/λ⁴ + 7.81×10¹¹ e^(−48.48/λ) + 154.2x/(46.6x + 60)·10⁻² e^(4.63/λ) + α_OH(λ) (λ in µm, dB/km)
Rayleigh scattering from frozen-in density and composition fluctuations falls as λ⁻⁴; A is 0.7–0.9 dB·km⁻¹·µm⁴ for silica fibres and rises with the core's germania content (Agrawal). The infrared tail of the Si–O vibrations and the ultraviolet tail of the electronic absorption are Keiser's empirical fits for GeO₂-doped silica (x = GeO₂ mole fraction). Scattering and the infrared tail cross near 1550 nm, which sets the minimum-loss window.
The OH band is drawn as a Gaussian of the given height at 1383 nm and an illustrative 30 nm FWHM. 1 ppm of OH by weight gives about 63 dB/km at the peak, so 0.5 dB/km means ≈ 8 ppb. G.652.D (low water peak) caps the 1383 nm loss after hydrogen ageing at the 1310–1625 nm maximum, 0.40 dB/km for cable.
Not included: waveguide imperfections and bending, the weak 1246 nm OH combination band (the 943 nm OH band is modelled, scaled from the 1383 nm peak), hydrogen ageing, and other impurities. The defaults (A 0.85, 4 mol % GeO₂) give 0.32 dB/km at 1310 nm and 0.19 dB/km at 1550 nm, typical of standard single-mode fibre.
Model and references
Textbook approximation. A standard approximation from the literature (for example paraxial, plane-wave or Gaussian-beam), valid within the range the page states. About the tiers
Rayleigh A/λ⁴ plus Keiser's empirical IR and UV tails for GeO₂-doped silica; the OH bands at 943 and 1383 nm are illustrative Gaussians (input height at 1383 nm). Bends, splices and other impurities not included.
- Agrawal G. P. (2010). Fiber-Optic Communication Systems, 4th ed. Wiley. Fiber losses: Rayleigh scattering A/λ⁴ with A ≈ 0.7–0.9 dB·km⁻¹·µm⁴. doi:10.1002/9780470918524
- Keiser G. (2010). Optical Fiber Communications, 4th ed. McGraw-Hill. Attenuation chapter: empirical infrared and ultraviolet absorption of GeO₂-doped silica.
- Osanai H., Shioda T., Moriyama T., Araki S., Horiguchi M., Izawa T., Takata H. (1976). Effect of dopants on transmission loss of low-OH-content optical fibres. Electron. Lett. 12, 549. Source of the absorption fits. doi:10.1049/el:19760418
- Humbach O., Fabian H., Grzesik U., Haken U., Heitmann W. (1996). Analysis of OH absorption bands in synthetic silica. J. Non-Cryst. Solids 203, 19. OH band positions and the 1383 nm strength, 62.7 dB/km per ppm (as quoted in arXiv:2303.17814, Table I). doi:10.1016/0022-3093(96)00329-8
- Philen D. L. (1982). Measurements of OH diffusion in optical-fiber cores. Bell Syst. Tech. J. 61, 283. 10 ppm of OH adds about 12 dB/km at 0.95 µm. doi:10.1002/j.1538-7305.1982.tb03407.x
- Hetherington G., Jack K. H. (1962). Water in vitreous silica. Part I. Influence of 'water' content on the properties of vitreous silica. Phys. Chem. Glasses 3, 129. Molar absorption coefficient 77.5 L·mol⁻¹·cm⁻¹ at 2.72 µm.