Study On The Sub-Aperture Stitching Optical System

Under given working wavelength condition, the resolution of optical system is limited by the aperture of entrance pupil. The fabrication of ultra-big optical system is constrained by optical material, cost and loading ability and so on. It is too difficult to realize. The fabrication of extreme large aperture element is too difficult to be realized. Application of sub-aperture stitching could dispatch fabrication to lower cost and keep accuracy.The key technology of design, fabrication, alignment and test in sub-aperture stitching optical system prototype is studied in this paper. The mainly work is explained as following:Based on the analysis, comparison and concluding of related paper and monograph, the developing history and present status is introduced. The imaging character of sub-aperture system is discussed. Due to the impact of sub- aperture distribution on the optical modulation transfer function, optical modulation transfer function is applied to evaluate the image quality of sub-aperture system. The sub-aperture distribution determination according . to the change of optical modulation transfer function is analyzed.In sub-aperture system with central obscuration, the central obscuration will not only decrease the energy but also affect the image quality of optical system. Based on the annulus diffraction theory, the mathematical model for optical system with central obscuration is built. The program is developed to analyze the image quality variation due to the central obscuration. It provides proof for reasonable selection of central obscuration. From the comparison of calculating result and the simulated result from program, the embedded program is verified.The conventional cassegrain optical system is modified that aspherical surface is substituted by spherical surface. The field of view is also enlarged. It is much more appropriate for sub-aperture stitching because there is no aspherical surface in the modified design. It is easier for the fabrication, alignment and testing of sub-aperture.The impact of sub-aperture distribution on optical modulation transfer function fordifferent F/# and the same F/# are analyzed. When the designed result approachesthe diffract limit, the simulating result is much more close to the practical condition. It provides proof for the demonstrating experiment with smaller aperture principle prototype.The "Cornwell+Annulus" sub-aperture distribution is proposed for the sub-aperture stitching prototype. The optical modulation transfer function effect of sub-aperture distribution is tested. It is shown that the testing result is uniform with the simulated result. The simulation reliability is certified.Based on analysis of optical system parameters, the modified cassegrain system is selected. The modified system facilitates the stray light reduction. The stray light of prototype is analyzed. The fabrication and alignment tolerance is proposed with equivalent nodal point concept of dynamic optics theory. The environmental performance of prototype is also analyzed. The scheme with reference of central annulus is proposed for testing of concentricity among sub-apertures and alignment of prototype.The auto-collimating optical path to test the concentricity among the sub-apertures and the central annulus could be realized through combination of small aperture auto-collimating component and rotary guide. The fabiricating difficulty of large aperture plane reflector in the auto-collimating testing of sub-apeture stitching system is solved.Based on these foundations,the sub-aperture stitching prototype is developed successfully.