Measurement of the birefringence in bulk optical media by using interferometric methods

Accurate knowledge of the index of refraction of an optical medium is of fundamental importance in various optical applications. We applied a Michelson interferometer and Fabry-Perot-type interference methods to a wafer sample to estimate the difference between two orthogonal indices, Δn, of a LiNbO₃ crystal wafer and we compared the results of the two methods. By measuring the transmittance with sample rotation, we obtained a beat pattern between the fringes of the ordinary and the extraordinary light waves. Fitting the node locations, we could determine the Δn value with an uncertainty of 10^-3 with both methods. Since the Fabry-Perot method is insensitive to atmospheric turbulence and vibration and is very simple to implement, it allow a quick estimate of the birefringence in optical crystals.