Investigation on a Dual Beam Fabry-Perot Interferometer

Laser interferometer is indispensable for precision displacement measurements and calibrations of linear actuator systems, e.g. precision machine tools, nano-positioning stages or semiconductor manufacturing equipments. Compared with Michelson interferometer with two optical paths along different axes, the significant characteristic of the common path in a Fabry-Perot interferometer enables to minimize the influence of environmental parameters. Due to multi-interferences, the conventional Fabry-Perot interferometer (FPI) suffers from the non-orthogonal interference signals that lead to possible interpolation errors while higher resolutions would be demanded. To improve the phenomenon, a coaxial dual-beam Fabry-Perot interferometer (FPI) has been developed to facilitate high-precision linear displacement measurements in this article.By manipulating the polarization state and some specific optical components, the proposed interferometer can attain the goal of the coaxial path and orthogonal signals such that the above-mentioned concerns will be resolved. Theoretical simulations based on the modified innovative optical structure and preliminary experimental testing have revealed that orthogonal signals generated in the dual-beam FPI are able to overcome limitations of the conventional FPI. Interpolation simulations showed that the measurement accuracy has been enhanced by approximately 40 nm with this structure in comparison with the results from a conventional FPI.