Fumio Kobayashi

Coordinate-transform technique for closed-fringe analysis by the Fourier-transform method

A coordinate-transform technique is proposed that enables the Fourier-transform method to analyze an interferogram that includes a closed-fringe pattern. First, the closed-fringe pattern is converted to an open-fringe pattern by transformation of the Cartesian coordinate system to a polar coordinate system. Then the phase distribution for the open-fringe interferogram is determined by the conventional Fourier-transform method. The phase distribution for the original closed-fringe pattern is obtained by inverse coordinate transformation from the polar coordinate system back to the Cartesian coordinate system. Computer simulation and experiments were performed for a closed-fringe pattern generated by interference of a spherical wave with a reference plane wave, and results are presented that demonstrate the validity of the proposed technique.

High-precision measurement of a fiber connector end face by use of a Mirau interferometer

What we believe to be a new instrument for measuring the end-face geometrical parameters of fiber connectors is described. In this apparatus, a Mirau-type interferometric objective is employed to measure a small area of the connector end face and generate an interferogram corresponding to the surface profile. Various new technologies are used to ensure excellent performance and high measurement repeatability. A multipoint method is proposed to adjust the inclination of the physical contact sample stage. The physical contact angle of the sample stage is adjusted directly on the instrument by use of a special tool whose angle is calibrated with the reversal method. Measurement results of important parameters of the fiber connector end face are compared with those inspected by a commercial profiler or with a standard sample. Optical insertion losses of connectors inspected by the developed system are also evaluated.

Coordinate transform method for closed fringe analysis

A coordinate transform method is proposed which enables the Fourier transform method to analyze interferograms including closed fringe patterns. According to the principle of the proposed method, closed fringe patterns in an interferogram can be converted to open fringe patterns by transforming the Cartesian coordinate system to a polar coordinate system. Phases corresponding to the open fringe interferograms can be obtained by analyzing the open fringe interferograms using the conventional Fourier transform method. Subsequently, the original phases corresponding to the closed fringe interferograms can be acquired by inverse coordinate transform. Computer simulation and experiments show that spherical wave fronts are accurately recovered by using the proposed method.