Nonlinearity in a fiber-optic coupled heterodyne interferometer

A high-accuracy (nonlinearity < 2nm) fiber-optic coupled displacement heterodyne measuring Michelson interferometer is developed. The primary limitation of accuracy encountered with this fiber-optic coupled heterodyne interferometer is the optical mixing arising from the imperfection of fiber-optic coupling system. The optical mixing results in the nonlinearity (first order and second order errors) in the displacement measurement of the interferometer. A theoretical model using Jones calculus is developed; the corresponding experiments are implemented. The theoretical results are consistent with the experimental results.