Research On Off-axis Reflection Optical Systems Based On Computational Imaging

Off-axis reflection optical systems have many advantages: no chromatic aberration,no central obstruction,foldable optical path,easy to achieve large aperture and long focal length high-quality imaging,and are widely used in remote detection fields such as aviation and aerospace.Under the influence of asymmetric off axis aberrations,the field of view in the Y direction of traditional off-axis reflection optical systems is very small.Generally,it is need to use freeform surface elements in the system to correct off-axis aberrations to achieve the purpose of expanding the field of view.However,the introduction of freeform surfaces will greatly increase the difficulty of processing,testing,and assembling optical systems,resulting in high manufacturing costs and long production cycles.Therefore,it is necessary to deeply study the field of view expansion path of off-axis reflection optical systems.In recent years,computational imaging technology has developed rapidly.Its core idea is optical-digital joint design,which introduces computer algorithms into the process of optical imaging.The two work together to solve many traditional imaging technology problems.This article focuses on three aspects of "optics","digital",and "joint design".Firstly,this thesis studies the imaging characteristics of off-axis reflection optical systems.The structural types,vector aberration characteristics,and description methods of reflective surfaces of off-axis reflection optical systems are studied from the perspective of aberration correction;This thesis studies two existing methods of optically extending the field of view of reflective systems,and expounds the significance and importance of optical system field of view expansion from the perspective of remote detection.Then,the theoretical basis of computational imaging for off-axis reflection optical systems is studied.A method for constructing a continuous point spread function model for non-rotationally symmetric optical systems in the full field of view is proposed;Research the commonly used algorithms for computational imaging,and construct the algorithms used in this article by analyzing three typical image deconvolution algorithms and two commonly used iterative methods;Various image quality evaluation methods are discussed.Finally,two optical digital joint design methods for off-axis three mirror optical systems,namely,point spread function matrix scanning method and Zernike coefficient correlation aberration localization method,are proposed.The point spread function matrix scanning method obtains the Zernike coefficient matrix,constructs a continuous set of point spread function matrices in the full field of view based on the wavefront aberration model and the generalized pupil function,performs pixel by pixel scanning processing on blurred images in a large field of view,and performs an algorithm for correcting off axis aberration for each pixel point.Simulation experiments were conducted on an off axis three mirror optical system with a focal length of 260 mm,with an initial field of view of 8 ° × 1 °,using matrix construction to expand the field of view to 8 °× 6 ° without using freeform surfaces,good imaging quality,full field MTF greater than 0.4.The Zernike coefficient correlation aberration localization method accurately constructs an aberration processing algorithm by using Zernike polynomial free form surfaces to locate the severe aberration terms of the off-axis three mirror optical system.The simulation design of an off axis three mirror optical system with a focal length of 1000 mm is carried out.Initial field of view is 6 ° × 1 °,using Zernike polynomial freeform surfaces at three mirrors to increase the field of view to 6 ° × 5°;Obtain the coefficients of the freeform surface,determine the type of aberration that causes blurring in the imaging of the optical system,and construct an aberration correction algorithm;By removing the higher order terms of a free form surface and retaining only the quadratic coefficients,an off axis three mirror optical system without a freeform surface is obtained;At this time,the off-axis aberration of the system is not corrected;Finally,the constructed aberration correction algorithm is used to eliminate imaging blurring caused by expanding the field of view,achieving the goal of expanding the field of view.In this thesis,the problem of small single direction field of view in off axis reflective optical systems is studied.Combining the advantages of computational imaging technology,an optical digital joint design method for off axis reflective optical systems is proposed.Without using free form surfaces,the Y direction field of view of off axis three mirror optical systems is expanded,and rectangular field of view imaging is achieved.