Research On Aperture Synthesis In Infrared High Sensitivity Imaging Systems

The resolution of optical systems is proportional to the diameter of its aperture. However the aperture size is limited by the volume, mass and manufacturing cost of the primary mirror. Synthetic aperture optical systems can obtain the resolution of a large aperture optical system with several sub-apertures, which makes the system lighter and less expensive to manufacture than mono aperture optical systems. Large aperture space borne optical systems are costly to launch due to the volume and mass limit of launch vehicles, which makes synthetic optical systems competitive in cost and promising in future space imaging applications.The development in synthetic aperture optical systems are researched. The working principles of Michelson and Fizeau synthetic aperture optical systems are studied, and the key techniques for u-v coverage, compensating the optical path difference between sub-apertures, and image reconstruction are elaborated respectively. The proper application scenes for these two kind of synthetic aperture systems are discussed.According to the need of earth observation optical systems, an infrared Fizeau synthetic aperture optical system employing push-broom technique is designed. The working wavelength is between 8μm and 10μm. The angular resolution parallel to the push-broom direction is enhanced by aperture synthesis, and the angular resolution perpendicular to the push-broom direction is enhanced by sub pixel technique. It is a catadioptric optical system based on Cassegrain structure. The imaging quality is enhanced with two sub-aperture structure. The tolerance is decided by software emulation, and alignment method is discussed. The irradiance at the image plane caused by thermal radiation of the components of the system under different temperatures is analyzed, and the low temperature needs to be reached to get proper SNR is determined. The change of refraction indices of transmission materials, and surfaces and spacing of optical elements are calculated, and the imaging quality of the system in cryogenic environment is simulated. The analysis shows that the structure is applicable, and performance meets the requirement. The combination of synthetic aperture and sub pixel can reduce the mass and lower the difficulty in manufacturing. This research should be helpful in exploring techniques to enhance the resolution of space borne optical systems.