Low Water Peak Fiber
Compare low-water-peak (G.652.D) and older single-mode fiber: loss at the 1383 nm OH peak, OH content, E-band average, the span loss of each CWDM channel, and the OH absorption bands of silica at 943, 1383 and 2722 nm.
Loss at 1383 nm
0.311 dB/km
OH content 0.797 ppb; older fibre 1.261 dB/km (15.9 ppb)
Water-Peak Check (G.652.D)
Meets
α(1383) ≤ 0.40 dB/km cable limit; also ≤ this fibre's α(1310) = 0.323 dB/km (stricter data-sheet criterion)
Worst CWDM Channel
14.55 dB
1271 nm over 40 km; older fibre 43.06 dB at 1391 nm
E-band Mean (1360–1460 nm)
0.259 dB/km
older fibre 0.552 dB/km
Attenuation Spectrum: Older vs Low-Water-Peak Fibre
O-band 1260–1360 nm, E-band 1360–1460 nm (the water peak), S-band 1460–1530 nm, C-band 1530–1565 nm, L-band 1565–1625 nm.
OH Absorption Bands, 0.8–2.9 µm
| Band (nm) | Assignment | dB/km per ppm OH | Low water peak (dB/km) | Older fibre (dB/km) | Strength source |
|---|---|---|---|---|---|
| 943 | 3ν₃ (second overtone) | 1.20 | 0.000957 | 0.0191 | Philen 1982 |
| 1246 | 2ν₃ + ν₁ (combination) | — | — | — | not modelled: no open source for the strength |
| 1383 | 2ν₃ (first overtone) | 62.7 | 0.0500 | 1.00 | Humbach 1996 |
| 2212 | ν₃ + ν₁ (combination) | — | — | — | not modelled: no open source for the strength |
| 2722 | ν₃ (fundamental stretch) | 1.00e+4 | 8.00 | 160 | Hetherington & Jack 1962 |
Peak OH excess of each band, scaled from the 1383 nm input by the OH content. Band positions from Humbach et al. (1996). Beyond about 2 µm the multiphonon absorption of silica itself dominates, so fibres do not transmit at the 2.72 µm fundamental.
CWDM Channel Span Loss (ITU-T G.694.2 grid, 40 km)
Model
α = A/λ⁴ + α_IR + α_UV + Σ C_OH · S_i · exp(−(λ − λ_i)²/2σ_i²), C_OH = α_OH(1383)/62.7 dB/km per ppm
Both fibres share the intrinsic silica loss (Rayleigh scattering, infrared and ultraviolet tails; see the attenuation calculator) and differ only in the OH absorption, from residual water in the glass. 1 ppm of OH by weight adds 62.7 dB/km at the 1383 nm first overtone, so a low-water-peak fibre holds its OH content to a few ppb; the same OH adds 1.2 dB/km per ppm at the 943 nm second overtone and about 10⁴ dB/km per ppm at the 2.72 µm fundamental, which follows from its molar absorption coefficient, 77.5 L·mol⁻¹·cm⁻¹. G.652.D requires the 1383 nm loss (after hydrogen ageing) to stay at or below the maximum specified for 1310–1625 nm, 0.40 dB/km for cable; many "zero-water-peak" data sheets promise the stricter α(1383) ≤ α(1310), shown alongside. The limits are cable values and this model is bare fibre, so the check is indicative. Older G.652.A/B fibres had no limit there, which made the E-band and the CWDM channels around 1371–1411 nm unusable over long spans.
Illustrative: each OH band is a Gaussian, 30 nm FWHM at 1383 nm and the same width in wavenumber elsewhere (an assumption), and the 1383 nm peak heights are inputs, not data for a particular fibre. Not included: splices, connectors, bends, and the 1246 and 2212 nm combination bands, whose strengths we have no open source for.
Model and references
Illustrative. A simplified model that shows trends and orders of magnitude. Don't use its numbers for design. About the tiers
Shared silica loss model (Rayleigh, Keiser IR/UV tails) plus Gaussian OH bands at 943, 1383 and 2722 nm scaled by the OH content (62.7, 1.2 and 1.0e4 dB/km per ppm); widths are assumed (30 nm FWHM at 1383 nm, the same in wavenumber elsewhere), the 1246 and 2212 nm bands are not modelled, and the OH peak heights are inputs, not data for a particular fibre.
- 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 strength (≈ 63 dB/km per ppm at the 1383 nm peak). doi:10.1016/0022-3093(96)00329-8
- Keiser G. (2010). Optical Fiber Communications, 4th ed. McGraw-Hill. Attenuation chapter: empirical infrared and ultraviolet absorption of GeO₂-doped silica.
- ITU-T G.694.2 (2003). Spectral grids for WDM applications: CWDM wavelength grid, 1271–1611 nm in 20 nm steps. itu.int
- ITU-T G.652 (2016). Characteristics of a single-mode optical fibre and cable. G.652.C/D: 1383 nm loss after hydrogen ageing at or below the 1310–1625 nm maximum (0.40 dB/km for cable). itu.int