The Sellmeier fit for fused silica gives the following refractive indices near 1550…

PHYSICS · Subjective · Fermi University Physics · Optics & Photonics · Wave propagation and light in media · Wave propagation and light in media

What an Instrument Can See, Ch The optical constants of a medium

Problem

The Sellmeier fit for fused silica gives the following refractive indices near 1550 nm:

n(1540\ \mathrm{nm}) = 1.44414

n(1550\ \mathrm{nm}) = 1.44402

n(1560\ \mathrm{nm}) = 1.44390

. Estimate the group index

n_g = n - \lambda\,dn/d\lambda

of fused silica at

1550\ \mathrm{nm}

, using a centred finite difference for the derivative.