Dual Interferometric Displacement Measurement System Incorporating a Wollaston Interferometer

A new optical displacement measurement system is presented using a dual interferometric design where a Wollaston prism interferometer is employed in conjunction with a normal Michelson interferometer. This is configured without the use of external polarizers, apart from those associated with the Wollaston prism. It is shown that an optical path difference induced in the Michelson interferometer can be detected using the Wollaston prism in a normal interferometer arrangement, despite the different modes of operation of the two interferometers (the Michelson splits input light by amplitude whereas the Wollaston prism splits light by polarization). Further, the interference pattern produced by the Wollaston prism interferometer changes in a measurable, linear fashion as the optical path difference from the Michelson interferometer alters, and as a result of the shape of the interference pattern, the need for calibration is reduced since a reference point is produced by the zero optical path difference point at the center of the Wollaston prism. A simple theoretical analysis of the system is presented and used to derive a computer model of the optical arrangement. Results from an experimental implementation of the system, using a Wollaston prism with a beam separation of 0.5 degrees and a superluminescent diode, of wavelength 825 nm, as a light source, are included and compared to the results from the computer model.