Design and implementation of a nanometer phase-shifting interferometer for micro-surface profile measurement

A vertical-shaft-type Mirau white-light phase-shifting interferometer is designed based on white-light phase-shifting interference microscopy in this paper. The interferometer is composed of an illumination and interference imaging part, a piezoelectric transducer in the vertical direction, a two-dimensional scanning part in the test surface, image collection and interferograms analysis part. The light illuminates the sample and the test surface uniformly, and the interferogram is formed. In order to get phase-shifting, the move of the objective is driven by PZT. The three-dimensional scanning system consists of a two-dimensional horizontal motorized stage and a vertical piezoelectric transducer. Multi-aperture stitching extends the measurement range in the test surface. A new pixel divided phase-extracting algorithm was put forward in combination with a residues-pretreatment phase-unwrapping algorithm based on image segmentation. The algorithm is used to minimize the phase-shifting error and nonlinearity error of the detector. The surface profile of a fiber connector with fiber inserted was measured. Mean value of the protrusion between fiber and fiber connector was measured to be 45.7nm, with 0.9 nm error. The mean height of a spot on the end surface of fiber connector was measured to be 23.6nm, with 0.7nm error.