Heterodyne interferometry is a widely applied technique for length and displacement measurements in precision systems. Free-space optical beam delivery couples the source directly to the interferometer location. Conversely, fiber delivery is desired to decouple the source and interferometer. Drawbacks to using fibers are either time consuming alignment (PM fiber) or time varying polarization output (MM fiber). Jones matrices were used to analyze Joo-type interferometers to simulate the effects of using MM fiber inputs. The results showed loss of interference at some instances from the rotating polarization states. Measurements with a MM fiber coupled interferometer showed minimal polarization rotation and no interference loss.
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