Research Of Off-axis Reflected System With Wide Field Of View Based On Vector Aberration Theory

With the development of space remote sensing technology and the increasing demand of remote sensing data application,people are more and more inclined to obtain optical remote sensing images covering a larger space and containing more detailed information.In the battlefield,disaster areas,accident areas and other areas with high timeliness requirements,in order to continuously obtain more comprehensive and accurate optical remote sensing information,it is necessary to conduct multiple high-resolution staring imaging or video shooting in a large area.This requires that the optical load not only has a long focal distance,but also has a wide field of view,that is,it has a large field of view in both the meridional direction and the sagittal direction.Off-axis reflective optical system is widely used in space optical loads with large field of view and long focal length because of its advantages of foldable optical path,no chromatic aberration,free from influence of material uniformity and physical and chemical properties,no central obstruction and insensitive to air pressure and ambient temperature.However,the existing off-axis optical system with long focal length can only achieve a large field of view in the sagittal direction and a small field of view in the meridional direction.This makes the system usually imaged in push-broom mode,and the satellite can only take one image at a time,so it is unable to obtain the continuous information of the target,and thus unable to detect the dynamics of the target.In view of the shortcomings of the existing off-axis optical system,this paper focuses on the design method of wide field of view and long focal distance axis reflection optical system,mainly using the vector aberration theory to control the aberration nodes of each optical surface of the off-axis optical system and the whole system to optimize the optical system.Based on this method,two kinds of wide field of view and long focal distance axial reflection optical systems have been designed,and one of them has been studied in the prototype development.The main research contents can be summarized as follows:1.Research on off-axis three-mirror optical system with wide field of view and long focal length.Firstly,several system schemes are compared according to the technical parameters of the system to be designed,and finally the design scheme of field offset off-axis three mirror optical system is determined.Then the initial structure of the system is calculated based on the differential equation method.This method first samples the light of the system,then obtains the coordinate values of the characteristic points on the secondary mirror and the third mirror by solving the differential equations of Fermat principle and Abbe sine theorem,finally fits the coordinates to obtain the surface formula of the secondary mirror and the third mirror,and then reaches the initial structure of the system.Then the system is optimized.In the process of optimization,based on the vector aberration theory,the node positions of coma and astigmatism of each optical surface and the whole system are controlled in the field of view to offset each other to the greatest extent,and the structure of the system is constrained meanwhile.In the later stage of design,in order to correct the residual aberration,the free-form surface is introduced into the system and deeply optimized.Finally,we obtained an off-axis three-mirror optical system with a focal length of 2000 mm,a field angle of 30 °×12 ° and a relative aperture of 1/5.2.Research on cooled infrared off-axis optical system with wide field of view and long focal length.Firstly,the design parameters such as field angle,focal length and relative aperture of the optical system are determined according to the resolution and width of the whole instrument,and based on these parameters,the detection performance of the whole instrument is analyzed,including noise equivalent temperature difference and maximum detection distance.Then,according to the characteristics of the system,the design scheme of combining the off-axis of the field of view and the off-axis of the diaphragm is determined,and the aperture diaphragm is placed between the three mirrors and the image plane to realize the cold aperture matching.Then,the initial structure of the system is solved based on the third-order Seidel aberration theory,the focal length formula of the system and the constraint on the position of the aperture.After the initial structure is obtained,the system is offsite,and structural constraints are added to eliminate light blocking.Then,the system is deeply optimized.In order to balance the aberration of each surface,the coma and astigmatism nodes of each optical surface and the whole system are controlled based on the vector aberration theory of aperture off-axis optical system,and the structural characteristics of the system are constrained combined with optical design software.Finally,we obtained a cooled infrared off-axis three-mirror optical system with a focal length of 500 mm,a field of view of 5.3 °×4.4 ° and a relative aperture of 1/2.3.Development of prototype of cooled infrared off-axis three-mirror optical system with wide field of view and long focal length.Firstly,the tolerance distribution and tolerance analysis of the system are carried out,and the allowable error range of processing error of mirrors and assembly error of system are given.Then the mechanical structure of the system is designed according to the light path layout characteristics of the system,and the light shield of the system is designed based on the structure,and the stray radiation is analyzed.Then it introduces the processing and detection methods of the mirror and the assembly and adjustment methods of the system.After the installation and adjustment,the modulation transfer function of the system is measured.The experimental results show that the cooled infrared off-axis three-mirror optical system with wide field of view and long focal length designed in this paper has excellent imaging performance and meets the application requirements.