An interferometer is a device that divides a light beam into two (or more) beams, which follow different optical paths before being recombined to cause interference. The most important parameter for interferometers is the optical phase retardation (or shift) or optical path difference (OPD) that results from the fact that different rays travels different optical distances after splitting. In the particular case of a polarization interferometer, the entering light beam is divided by a polarization-division

device into twobeamshaving orthogonal polarization directions.The first polarization interferometer was made by Jamin in 1868 (Jamin, 1868).