Research On Large Dynamic Range And High-precision Centroid Detection Method Based On A Dffraction Grating

In the application of the laser axis error detection and the photoelectric imaging tracking system,it is necessary to use the detector of the focal imaging far-field spot position to detect the target optical axis.The detector of the focal imaging far-field spot position generally includes a CCD camera.The position of the optical axis is detected by calculating the centroid deviation offset of the spot received on the CCD target surface.During the process of optical axis detection,the focal imaging far-field spot position detector is expected to have the ability of a large dynamic range and a high detection accuracy.The target optical axis has a degree of detection range and micro-radian alignment accuracy.The dynamic range and detection accuracy of the focal imaging far-field spot position detector are limited by the focal length of the imaging lens.Under the same size of the target surface condition,the detection accuracy of the optical axis can be improved by enhancing the focal length of imaging lens but the dynamic detection range of the optical axis will become narrow.Achieving the large dynamic range and high-precision detection is a contradictory process.In this paper,we hope to solve this contradictory process,and propose a new optical axis measurement method based on two-dimensional orthogonal diffraction grating,which makes the tilt tracking detector have the ability of large dynamic range and high precision detection.The incident beam is divided into a number of beams with the same incidence direction by the diffraction grating,and a spots array is focused on the CCD target surface.Compared with a single spot,the spot array has more spots input information,and the detection accuracy of the optical axis can be improved by increasing the information of the detected spot.At the same time,the range of the spots array distribution becomes larger than the area of the CCD target surface by using diffraction grating.When the main spot deviates from the target surface area,the displacement offset of the optical axis deviation can still be measured by the intensity distribution of the rest of spots array,thus the dynamic range of the optical axis is enlarged.In this paper,the principle of diffraction grating beam splitting characteristics to enlarge the optical axis of the dynamic detection range and improve the optical axis detection accuracy is primarily researched.For the two parts of large dynamic range and high precision detection,a comprehensive and deep research is carried out from three aspects: theoretical analysis,digital simulation and experimental verification.Firstly,the basic properties and the principle of diffraction grating are introduced.Then,the principle of enlarging the dynamic range of optical axis by using diffraction grating is analyzed in the theory.With the principle of large dynamic range,the numerical simulation is carried out.The dynamic range of the optical axis is measured by using the ?1st order diffraction spots.The numerical simulation results show that the diffraction grating can increase the dynamic range of the optical axis.Secondly,the imaging principle of two-dimension orthogonal diffraction grating are introduced in this paper.And high-precision spots centroid are detected by applying the orthogonal diffraction grating.The source of main error in the process of detecting centroid is analyzed theoretically.and the high precision centroid detection method is deduced from the detected spots array.According to the method of highprecision centroid detection,the numerical simulation is carried out.And the numerical simulation results are in accordance with the theoretical analysis.Finally,in order to verify the correctness of theoretical analysis and simulation results,an optical experiment platform based on diffraction grating is set up.The data of far-field spot images are collected by the CCD camera data acquisition software.After dealing with the spots data,the experimental results respectively verify that the optical axis dynamic range become enlarged and the optical axis detection accuracy can be improved at the same time.In total,applying the method proposed in this paper to detect the optical axis,the focal imaging far-field spot position detector can have the capability of the larger dynamic range and high-precision optical axis error detection.It is a significant research in the application scene of the laser axis error detection and the photoelectric imaging tracking system where the optical axis needs to be detected.