High-NA fiber point-diffraction interferometer for three-dimensional coordinate measurement

The numerical aperture (NA) and power of diffraction wave in point-diffraction interferometer (PDI) could significantly limit the measurement range of the system. A fiber point-diffraction interferometer with high NA is proposed for the measurement of absolute threedimensional coordinates. Based on the single-mode fiber with submicron aperture, the diffraction wave with both high NA and high power is obtained, by which the achievable measurement range of the PDI can be extended. A double-iterative method based on Levenbery-Marquardt algorithm is proposed to determine the three-dimensional coordinates under measurement. Numerical simulation and comparison experiments have been carried out to demonstrate the accuracy and feasibility of the proposed PDI system, with both high measurement precision and nice repeatability achieved.