Y-shaped Multi-pinhole Interferometer And Its Application To Absolute Coordinate Measurements

Since Michelson interferometer is invented, optical interferometry has been developed very quickly, and widely used in the distance measurement. Absolute distance measurement is a measurement of non-rail technology. It refers to a measurement that does not need to set up a rail between the two measured points. With industrial development, the problems of high-precision measurement of large length are becoming more and more important., these problems should be solved in poor conditions commonly. It is difficult to solve these problems using traditional measurement. So the absolute distance measurement technology is promoted, and a number of absolute distance measurement methods are developed, such as white-light interferometry, multi-wavelength interferometry, heterodyne interferometry, laser self-mixing interferometry. Absolute distance measurement technology simplifies the structure of the measuring instrument and measurement process, and avoids the measurement error caused by the cumulative count. However, it is hard to expand these approaches into absolute 3D coordinate measurement. An approach of absolute 3D coordinate measurements is based on the two point-diffraction phase-measuring interferometer proposed by Rhee recently. Although this method can be used to measure the 3D coordinate, it is not satisfactory. Because the method needs a complex phase shifting technique and an iterative algorithm. And it should collect at least three interference patterns to complete the measurement. It could not complete in real-time measurement. In this paper, we present a new approach of absolute 3D coordinate measurement, which is based on a multiple-pinhole interferometer that is intended to straightway measure the xyz-coordinates of the target moving in three dimensions. Main contents are as follows:1. The history of optical interference measuring has been introduced concisely. Sum up many typical of distance measurement methods. Mainly introduces the principle of multiwavelength interferometry, heterodyne interferometry, white-light interferometry, laser self-mixing interferometry, point-diffraction interferometry, and the advantages and disadvantages of each type of measuring method.2. A method for measuring wavefront by a Y-typed multi-pinhole plate is presented. In this method, the complex amplitude of a wavefront sampled by the Y-typed multi-pinhole plate inserted between the object and the detector plane can be extracted directly from the Fourier transform of a far-field diffraction intensity pattern without the need for any iterative algorithm. The phase retrieval process is carried out in each diffraction pattern without involving in other diffraction patterns. Therefore, we can immediately retrieve the phase as soon as one diffraction pattern is obtained in the scanning process. This method can speed up the imaging process, making the realization of real-time coherent diffractive imaging more feasible. In this paper the principle of the method is introduced, the feasibility of the method is proved by experimental results, and the influencing factors of imaging results are analyzed such as the number of sampling points, the diffraction distance and so on.3. A new method which is based on Y-typed multi-pinhole interferometer is proposed to measure absolute 3D coordinate. The method is based on the principle of wavefront measurement by using Y-typed multi-pinhole interferometer. The 3D coordinates of the target is found out by an effective algorithm using some discrete phase values on the measuring pinholes of the MP plate. These phase values can be directly extracted from the Fourier transform of a far-field diffraction intensity pattern. In this paper, the feasibility of the method is proved by computer simulation experiment. The error and the uncertainty of this measurement are analysed. This method has the advantages: the experimental setup is simpler and the phase retrieving is direct without the need of phase-shifting algorithm. And in this method, the coordinates could be calculated with one recorded diffraction pattern. This method could provide an valuable choice for real-time 3D coordinate measurement due to its high precision, simple structure and wide wavelength suitability.