Analysis And Simulation Of Misalignment Error In Splicing Fresnel Lens

Due to the advantages of light weight,easy to reproduce and relatively loose surface deformations,the thin-membrane Fresnel lens has a broad application prospect in the future huge-aperture astronomical telescope.In order to realize the large diameter,the Fresnel lens can only be realized by the technology of sub-mirror splicing.In the process of sub-mirror stitching,the misalignment between the sub-mirrors caused by various factors will affect the imaging quality of the primary mirror.In this paper,we do the following work about the analysis,detection and related experiments of misalignment errors of the Fresnel lens:1.Large astronomical telescopes at home and abroad,the main sub-mirror alignment detection technologies and imaging principle of Fresnel lens are investigated,and Combining with the research background and present situation,the purpose and significance of this study are put forward.2.The numerical simulation model of two piece and multichip Fresnel lens is set up.Then based on the theory of diffraction optics,the analytical expression of the point spread function of the primary mirror is deduced.The influence of each misalignment error on the image quality of the splicing mirror is analyzed,and the error tolerance of each misalignment error is calculated according to the Strehl criterion.3.Combining the imaging characteristics of Fresnel lens and analysis results of the influence of misalignment error on the imaging quality,a new method is proposed to detect the misalignment errors based on the point spread function image and the light self-collimation angle measuring principle.The principle and the concrete steps of the method are introduced in detail,and the method is verified by ZEMAX software.The results show that the method can effectively detect a variety of misalignment errors in the splicing lens,and the accuracy can meet the requirements of the error tolerance of ideal imaging.4.According to the misalignment error detection scheme presented in this paper,the corresponding experimental platform is designed,which contains two experiments.In experiment 1,a two-piece splicing Fresnel lens with a diameter of 40 mm and a focal length of400 mm is designed.The PI six-dimensional adjustment station is used as the sub-mirror error correction control system,and the ESDI interferometer is used as the parallel light source and the light self-collimation angle measuring system.Firstly tilt errors around X\Y axis of sub-mirror are measured base on the light self-collimation angle measuring system.Then,the point spread function image is obtained by CCD in the focal plane of the splicing lens,which can be used to measure the translation errors along XYZ axis of sub-mirror.The schemeachieves high precision alignment of sub-mirrors.Its detection precision is as follows: the standard deviation of ?Z is 27.2?m,the standard deviation of ?X and ?Y is 0.26?m,and the detection error of ?X and ?Y is less than 0.1 degrees.In experiment 2,the splicing lens whose misalignment errors have been corrected in experiment 1,are detected by interferometry.According to the characteristics of the Fresnel lens,the technology of self collimation interference detection is adopted,and the 4D dynamic interferometer is used as the measuring instrument.By adjusting the position of the interferometer and the plane mirror,the wavefront data of the splicing lens is obtained.Its optical wavefront is 0.26 ?,which is basically in accordance with Rayleigh criterion.The result shows the feasibility of the proposed scheme.