2 May 2009 Increasing mid-frequency contrast in sparse aperture optical imaging systems
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Abstract
Sparse aperture imaging systems are capable of producing high resolution images while maintaining an overall light collection area that is small with respect to a fully filled aperture yielding the same resolution. However, conventional sparse aperture systems pay the penalty of reduced contrast at mid-band spatial frequencies. The modulation transfer function (MTF), or normalized autocorrelation, provides a quantative measure of both the resolution and contrast of an optical imaging system. Numerical MTF calculations were thus used to examine mid-band contrast recovery through the systematic increase of autocorrelation redundancy in a Golay-9 sparse array. In a Golay-9 sparse aperture arrangement, three sets of three sub-apertures can be shown to lie at unique radii from the center of the array. In order to increase the mid-frequency contrast we then have two options. The first, and most influential, is to increase the size of the sub-apertures located at the intermediate radius from the array origin. This directly increases autocorrelation redundancy at mid-band frequencies. The second option, though less effective, is to increase the relative mid-band frequency response by attenuating the outer most sub-apertures. We will demonstrate that by increasing the diameters of the mid-radii sub-apertures, mid-band contrast can be increased by over 45%, compared to uniform sub-aperture diameter arrays. We will also demonstrate that attenuating the outer most sub-apertures can further increase mid-band contrast recovery, but only by less than 1%. The effects on array fill factor will also be discussed.
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Andrew J. Stokes, Andrew J. Stokes, Bradley D. Duncan, Bradley D. Duncan, Matthew P. Dierking, Matthew P. Dierking, Nicholas J. Miller, Nicholas J. Miller, "Increasing mid-frequency contrast in sparse aperture optical imaging systems", Proc. SPIE 7323, Laser Radar Technology and Applications XIV, 73230M (2 May 2009); doi: 10.1117/12.817837; https://doi.org/10.1117/12.817837
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