Linear measurement of static phase change in optical homodyne interferometers: an analysis

A new highly accurate linear method of dc phase-shift measurement based on spectrum analysis in a general optical homodyne interferometer is presented. The dc phase is superimposed onto a controllable ac phase modulation. The dc phase error is theoretically analyzed based on the excellently matching predicted and experimental reports of ac phase error. Significantly, for low values of dc phase, a constant correction factor can be utilized that leads to an ultralow minimum detectable dc phase shift.