A non-contact distance sensor with spectrally-spatially resolved white light interferometry

A non-contact distance sensor with spectrally-spatially resolved white light interferometry (SSRI) is proposed. With a charge coupled device (CCD) camera and a beam splitter added to the typical experimental setup of spectrally resolved interferometry (SRI), the spatial white light interferogram and the spectrum are recorded simultaneously. The two interferograms are used to measure distances in different measuring ranges. Adopting the proposed method, the dead zone of SRI measuring range is eliminated by analysing the shift of zero-order interference fringe in CCD camera field. In addition, the distance sign (positive or negative) of SRI is determined by analysing the nonlinear spectral phase caused by a dispersive plate, leading to the double extension of the measuring range. An experiment is performed to verify the advantage of this method. The root mean square (RMS) of 20 consecutive distance measurement errors is 0.013 μm and the measuring range is successfully extended to -160 to 160 μm from 8 to 160 μm, which demonstrates that the new method is effective to overcome the measuring range limits of SRI.