Research On Optical Design With Large Field Of View Based On Free-from Surface And Stray Light Suppression

With the rapid development of space remote sensing technology,the optical system with large aperture,long focal length,light weight and large field of view has become the development direction of the new generation of space optical system,the traditional spherical and aspheric surfaces are often unable to satisfy the design and application of high-performance optical systems.The appearance of free-form surfaces changed this situation.Free-form surface optical elements with non rotational symmetry structure can provide more design freedom,make the structural layout of the system more flexible and compact,and can improve the correction ability of out of axis aberration,make the system structure simplification and lightweight,widely used in various fields,especially the application of some particular scenario.In addition,the off-axis reflective optical system has become a hotspot in the design of space optical system due to its advantages such as non-central occlusion,efficient folding of optical path,compact structure,non-chromatic aberration and wide working band.However,the traditional off-axis reflective optical system with spherical or aspheric surface still has some problems,such as small effective field of view and insufficient simplified structure.The free-form surface is applied to the off-axis reflective optical system,and the advantages of the free-form optical element are used to make up for the shortcomings of the traditional off-axis reflective optical system.And it widens the field of view of the system and can correct the high-order aberration of the system well.In this paper,for the large field of view,long focal length space optical system,the following research is carried out on the free-form off-axis three-mirror system:Firstly,investigate the design of optical systems with freeform surfaces at home and abroad;analyze and study the relationship between the field of view and the third-order wave aberration expression of vector aberration theory in non-rotationally symmetric optical systems;elaborate the different description forms of freeform surfaces and point out the advantages and disadvantages of their respectivedescription forms;investigate application of freeform surface in imaging and non-imaging fields.Secondly,calculate the relevant structural parameters of the optical system,compare the advantages and disadvantages of the four types of optical systems,introduce the different structural forms of the reflective optical system,analyze the structural characteristics of off-axis three-mirror system,and complete the structural selection of the optical system.Thirdly,calculate the initial structure of the coaxial optical system,conduct off-axis processing on the coaxial optical system,and improve the performance of the system by taking advantage of Zernike polynomial freeform surface,optimize the field of view in the sagittal direction to 20°.Finally,an optimized off-axis tri-reflective optical system with a field of view of 20°×20°,a focal length of 1500 mm,and an entrance pupil of 150 mm is optimized.The MTF value of the entire field of view of the system is greater than 0.5 at @50lp/mm,and the system is more compact through structural restrictions,and the tolerance analysis of the system is carried out.Fourthly,considering the space environment and the serious impact of stray light on the optical system,a new type of baffle based on the horn tube effect is designed.By optimizing the design of the internal suppression structure of the baffle to improve the level of stray light suppression.Combined with the designed optical system,the stray light suppression effect of the baffle is compared with the traditional baffle,the results show that at an off-axis angle of 35° to 60°,the PST value of the baffle with horn tube is one order of magnitude lower than that of the baffle with vertical vane,and it has better stray light suppression effect.