Simple heterodyne interferometer using a polarizing beam displacer

A novel, to the best of our knowledge, and simple heterodyne interferometer that uses spatially separated input beams to minimize the influence of the periodic nonlinearity is constructed. A custom designed polarizing beam displacer is used to split the input beams to parallel outputs with orthogonal polarizations, which provides a balanced path and completely symmetric structure for the interferometer. This novel optical setup suppresses the nonlinearity caused by the frequency and polarization mixing, and the very simple optical structure makes the interferometer less susceptible to environmental turbulence with potential use in many sensor applications. Experiments have confirmed that the interferometer maintains sub-nanometer nonlinearities in the laboratory environment.