Optical System Design for Wide-area Spatial Sensitizer
Satellites and spacecrafts should possess functions as alarm and avoid through observation in the future.Hence,spatial perception is carried on spatial objectives,such as satellites,space debris and asteroids,etc.Aiming to capture and identify both point and area target,perception sensor is provided with double properties of star sensor and optical camera.In the past design examples,Modulation Transfer Function(MTF)of optical cameras reached greater than 0.45 at 70 lp/mm.The resolution ratio could meet the needs of conventional space applications.However,the sensitivity of cameras detecting fixed stars will be limited,as a result of selecting effective aperture on the basis of diffraction limit of resolution ratio.Star sensors detect high magnitude stars through relatively large apertures,on the other hand,the field of view is smaller than that of cameras'.Usually,diffused light spots are taken as evaluation function of optical systems of star sensors,and the MTF design is demanding moderately.In the light of technical weaknesses of the above mentioned two optical systems in the application of engineering,this paper designs an optical system which is applicable to wide-area spacial perception sensors,based on target equivalent magnitude model and optical imaging link mechanism,and combined with photoelectric sensing devices.In order to solve the technical problems in the process of engineering,the paper conducts an overall indicator demonstration from the perspective of optical system,based on the application background,and subsequently carries out optical path design and image quality evaluation.The optical system is designed as with full field design value of 60°,the theoretical F value of 3.0,distortion of-0.55%,magnification color aberration of less than 2 μm,and energy concentration of 100%within 15 μm.To maintain consistent sensitivity of the detector center and edge to fixed stars,the optical system uses quasi-image telecentric design scheme,with the incident angel of principle ray of 8°.In the meantime,negative vignetting design scheme is applied to improve the illumination of edge images,and the illumination of the edge is 73%of that of the center eventually.The MTF of point target of the optical system is greater than 0.75 at 50 lp/mm(the following MTFs are based on this value as a reference).The MTF of area target is greater than 0.6 at 30 meters,and greater than 0.4 at 15 meters.In order to make the optical system engineering oriented,reduce installation costs,and optimize the optical path with low sensitivity,design steps are as follows.The first step is to use desensitization design method of"θ-Segmentation",optimizing the incidence angle of edge field of view each mirror in the optical path,and constructing a low sensitivity error control function with the sum of squared incident angles as the core.The second step is to introduce refractive angle control to search for a wider optimization space in the process of desensitization iteration optimization.The third step is to conduct tolerance analysis and iteration of beam entry/refraction angle.Specifically,based on the results of tolerance analysis,focus on optimizing the mirror in/out angle that has the greatest impact on optical image quality degradation.At the same time,release the mirror in/out angle that has the least impact on optical image quality degradation.The optimized optical path has a maximum incident angle of no more than 32° and a maximum refractive angle of no more than 30°.The last step is proposing to compensate for the MTF of point and area targets through defocus,so that the transfer function is not less than 0.4 at 50 lp/mm.In order to verify the theoretical analysis,the performance of the lens is tested in the article,and sensitivity and accuracy are tested through field observation experiments.The lens performance test results show that the MTF of the optical system is greater than 0.5 under the above assembly tolerance conditions;The illumination of the edge field of view is 72%of that of the center field of view;The maximum distortion is-0.58%;The maximum incident angle at the edge is 8.25°;The energy concentration within the 13.5 μm diameter of the diffuse is not less than 90%;The absolute value of the chromatic aberration between 500 nm and 800 nm wavelengths does not exceed 1.53 μm in the full field of view range.The outfield stargazing shows that the maximum sensitivity of the optical system is 6.4 Mv;The average angle measurement accuracy is 0.7",with 3σ confidence interval of 2"～3".This article provides some reference for other optoelectronic sensors regarding the analysis methods of optical system indicators,optical system design methods,and testing verification methods.
Electron bombarded active pixel sensorOptical designLow sensitivity tolerance optimizationLens testing
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