The comparison of two kinds of fiber phase shifting point-diffraction interferometer

The point diffraction interferometer (PDI) is the technology which realizes the absolute interferometric measurement without the use of reference surface. Pinhole is mostly used to generate the ideal spherical wavefront traditionally. While using the single mode optical fiber instead of pinhole can easily introduce phase-shifting ability for PDI measurement. This paper mainly discusses the merits and disadvantages of two kinds of fiber phase shifting point diffraction interferometer (FPS/PDI). Two fibers FPS/PDI is a separated-path configuration. Although it's easy to adjust, it's more sensitive to environment influence, and the thickness of fiber cladding will induce an off-axis error during measurement. Single fiber FPS/PDI is a common-path configuration, thus it is robuster than the front, but the maximum visibility is now one half. Its accuracy is mainly affected by factors such as the fiber core diameter, slight ellipticity and oblique face. The paper lastly compares the single fiber PDI with ZYGO interferometer based on measurement data about a sphere surface, the single interference pattern collected by our experimental fiber PDI apparatus is analyzed and the major error sources are also discussed.