Fiber Characterization

Step-index fiber parameters from the core and cladding indices and core radius: V, cutoff, MFD, effective area and index, nonlinear γ, core confinement and datasheet dispersion.

Model: Textbook approximation

Wavelength (nm)Core Index n₁Cladding Index n₂Core Radius (µm)Zero-Dispersion λ₀ (nm)Zero-Dispersion Slope S₀ (ps/nm²/km)

V-number

2.072

Single-mode

Theoretical LP11 cutoff

1335 nm

λc from a and NA; measured fibre and cable cutoffs are lower

MFD

10.08 µm

Gaussian fit; Petermann II 9.88 µm

Effective area

79.8 µm²

π w² (Gaussian fit)

Nonlinear γ

1.32 /(W·km)

2πn₂/(λA_eff), n₂ = 2.6e-20 m²/W

Numerical aperture

0.1246

Acceptance half-angle 7.16°

Relative index Δ

0.370 %

(n₁² − n₂²)/(2n₁²)

Effective index

1.44636

b = 0.4389; 76.0 % of power in the core

Dispersion D

17.46 ps/(nm·km)

From λ₀ and S₀ you enter (datasheet), not from the geometry

V-number vs Wavelength

Mode Field Diameter vs Wavelength

Model

V = 2πa·NA/λ, NA = √(n₁² − n₂²), λc = 2πa·NA/2.405

w/a = 0.65 + 1.619/V^1.5 + 2.879/V^6, A_eff = πw², γ = 2πn₂/(λA_eff)

n_eff² = n₂² + b(n₁² − n₂²), b = W²/V², D = (S₀/4)(λ − λ₀⁴/λ³)

Weakly guiding step-index fibre with the exact LP01 eigenvalues (Gloge 1971), Marcuse's Gaussian MFD fit and the exact Petermann II MFD. Defaults are an SMF-28-like step equivalent with phase indices (pure-silica cladding 1.4440 at 1550 nm). Dispersion uses the ITU-T G.652 form with your λ₀ and S₀; waveguide dispersion of the step profile is not computed.

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

Step-index LP01 (Gloge): V, cutoff, b, n_eff, core power, Petermann II and Marcuse-fit MFD, A_eff and γ. Weak guidance (Δ ≪ 1); Marcuse fit for 1.2 < V < 2.4; cutoff is the theoretical LP11 value. D uses the G.652 λ₀/S₀ form you enter, not the geometry.

Gloge D. (1971). Weakly Guiding Fibers. Appl. Opt. 10, 2252. LP modes, eigenvalue equation and core power fraction. doi:10.1364/ao.10.002252
Marcuse D. (1977). Loss Analysis of Single-Mode Fiber Splices. Bell Syst. Tech. J. 56, 703–718. Gaussian fit of the mode-field radius. doi:10.1002/j.1538-7305.1977.tb00534.x
Agrawal G. P. (2019). Nonlinear Fiber Optics, 6th ed., §2.3. Academic Press. Nonlinear coefficient γ = 2πn₂/(λA_eff). doi:10.1016/C2018-0-01168-8
ITU-T G.652 (11/2016). Characteristics of a single-mode optical fibre and cable. D(λ) = (S₀/4)(λ − λ₀⁴/λ³). itu.int

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