Fiber Delay Line Calculator
Calculate group delay, dispersive pulse spread, thermal delay drift and loop FSR for fiber optic delay lines.
Results
Propagation delay:489.672 ns
Group velocity:2.0422 × 10⁸ m/s
Group path n_g·L:146.80 m
Bit slots stored:4896.7 bits
SMF dispersion D(λ):17.46 ps/(nm·km)
rms dispersive spread:0.175 ps
Delay change vs 25 °C:37.40 ps
Loop FSR:2.0422 MHz
Narrow source (σ_λ < 3λ²B/c): the broad-source spread above underestimates the broadening.
Formulas
τ = n_g · L / c
FSR = c / (n_g · L)
D(λ) = (S₀/4)(λ − λ₀⁴/λ³), S₀ = 0.092, λ₀ = 1310 nm
σ_D = L·√((Dσ_λ)² + ½(Sσ_λ²)²)
Δτ_T = (dτ/dT per km) · L · ΔT [SMF-28: 37.4 ps/(km·K)]
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
Group delay n_g·L/c, loop FSR and G.652 dispersion. Thermal coefficient 37.4 ps/(km·K) measured on SMF-28 (special coatings differ). The dispersive spread assumes a broad Gaussian source.
- Slavík R. et al. (2015). Ultralow thermal sensitivity of phase and propagation delay in hollow core optical fibres. Sci. Rep. 5, 15447. SMF-28: 37.4 ps/(km·K) measured, 39 calculated. doi:10.1038/srep15447
- ITU-T G.652 (11/2016). Characteristics of a single-mode optical fibre and cable. D(λ) = (S₀/4)(λ − λ₀⁴/λ³) with 1300 ≤ λ₀ ≤ 1324 nm and S₀ ≤ 0.092 ps/(nm²·km). itu.int
- Agrawal G. P. (2010). Fiber-Optic Communication Systems, 4th ed., §2.4. Wiley. doi:10.1002/9780470918524