Group Refractive Index Calculator

Find group index using dispersion or velocity. Supports multiple unit choices and optional fiber length. Download CSV or PDF for reports and teaching needs.

Calculator
Choose a method, fill inputs, then calculate.
Pick based on what data you have.
Used to compute total group delay.
λ is converted internally to meters.
Use phase or effective index at λ.
Sign matters. Many materials have negative dn/dλ.
Formula Used

Dispersion form (wavelength):

ng = n − λ (dn/dλ)

Here, n is the phase (or effective) refractive index at wavelength λ. The slope dn/dλ is the index change per unit wavelength.

Group velocity form:

ng = c / vg

Once ng is known, the group delay per meter is τ/L = ng / c, and the total delay is τ = (ng L) / c.

How to Use This Calculator
  1. Select a calculation method that matches your available measurements.
  2. For dispersion form, enter λ, n, and dn/dλ with correct units.
  3. For group velocity form, enter vg and its unit.
  4. Optionally enter a propagation length to compute total delay.
  5. Press Calculate to view results above the form, then export if needed.
Example Data Table

These examples are illustrative for testing input formats.

Method λ n dn/dλ vg Length Output ng
Dispersion form 1550 nm 1.444 -1.0e-5 1/nm Auto 10 m 1.45950
Group velocity form Not required Not required Not required 2.05e8 m/s 100 m 1.46240
Dispersion form 850 nm 1.500 -2.0e-5 1/nm Auto 1 km 1.51700