Absolute Interferometric Measurement of Differential Displacements

The paper describes an interferometric technique suitable for the absolute measurement of displacements with nanometer resolution over a range up to few hundreds of micrometers. The displacement pick-ups are linked with optical fibers. The laser source is a VCSEL operated with a continuous wavelength modulation. The measurement is obtained combining absolute frequency-based measurements with phase-based measurements. The uncertainty analysis shows the conditions that must be fulfilled to get the best results. To build a compact sensors it is proposed the use of a DOE as a beam splitter and fiber coupler.