Precision polarization multiplexed heterodyne acousto-optic interferometric sensor

Proposed and demonstrated is an angstrom level optical path length (OPL) detection sensitivity polarization multiplexed heterodyne acousto-optic interferometric sensor. Because both the phase-coded and the reference rf signals in the design are generated by the same optics, the heterodyne detected rf signals generated contain correlated phase noise characteristics that essentially cancel out during the mixing process in the rf domain. Hence, the proposed four-beam design leads to a super stability OPL sensor with angstrom level experimentally demonstrated measurement stability. A proof-of-concept experiment measures the voltage-dependent phase change due to the refractive index change of a liquid crystal sensor chip.