On the influence of Earth’s rotation on light propagation in waveguides

We analyse the influence of Earth's rotation on the propagation of light in optical media. This is done using both geometrical optics and a perturbative calculation based on Maxwell's equations in rotating coordinates in flat spacetime. Considering light propagation in cylindrical step-index waveguides in particular, the first order correction to electromagnetic modes is computed. The calculation shows that Earth's spin causes a weak mode coupling, giving rise to sidebands, whose amplitudes are computed as well. The correction to the dispersion relation derived here allows to assess the anisotropy of light propagation due to Earth's rotation. The linearisation of this result is found to agree numerically with a simple formula derived from geometrical optics.