A VISAR (velocity interferometer system for any reflector) determines the velocity of a moving object by measuring the Doppler shift with an unequal path length interferometer. This paper analyzes the configuration in the case where the optics are not perfect, (i.e., beam splitters not 50%, waveplates not exact or misaligned, improper polarization, etc.). It is shown that perfect interferometric information can be recovered even with far from perfect optical components.
Barry T. Neyer,
"VISAR error analysis and enhancement", Proc. SPIE 2002, Ultrahigh- and High-Speed Photography, Videography, and Photonics '93, (11 October 1993); doi: 10.1117/12.161371; https://doi.org/10.1117/12.161371