Experimental research on wave-front coded imaging technique applied to large aperture space-borne optical camera

Abstract

Nowadays, large aperture space-borne optical camera is one important payload used to capture optical images of space targets based on satellite platform, but many factors could prevent space-borne camera from obtaining satisfactory images. Firstly, vibration during launch, moisture absorption, deflation and violent temperature variation and so on could make the focal plane of space-borne camera deviate from its ideal position. Secondly, space targets are usually distant, moving quite fast and especially noncooperative targets may even appear in unknown distances. In this case, frequent, rapid and precise on-orbit focusing mechanism are indispensable to traditional imaging system, but wave-front coded imaging provides another choice. In wave-front coded imaging system, by introducing a suitably designed phase mask, the optical transfer function will become insensitive to defocus and the clear images similar to diffraction limited ones could be obtained through digital restoration. Therefore in this manuscript, the experimental research is carried out to investigate the effectiveness of wave-front coding technique in realizing high-resolution imaging without introducing any focusing mechanisms. By only adding a cubic phase mask to the exit pupil with diameter of approximately 80mm and keeping other optical-mechanical structures of a prototype large aperture camera with focal length of 6000mm and aperture of 600mm unchanged, the extension of depth of focus could be obtained. In the collimator based testing, the depth of focus of that prototype space-borne camera could be extended 8.5x approximately, which provides another way to realize high-resolution imaging of space targets while designing space-borne optical camera in future.