24 September 2009 Optical configuration of an upconverted millimeter-wave distributed aperture imaging system
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Abstract
Millimeter-wave (mmW) imaging is presently a subject of considerable interest due to the ability of mmW radiation to penetrate obscurants while concurrently exhibiting low atmospheric absorption loss in particular segments of the spectrum, including near 35 and 94 GHz. As a result, mmW imaging affords an opportunity to see through certain levels of fog, rain, cloud cover, dust, and blowing sand, providing for situational awareness where visible and infrared detectors are unable to perform. On the other hand, due to the relatively long wavelength of the radiation, achieving sufficient resolution entails large aperture sizes, which furthermore leads to volumetric scaling of the imaging platform when using conventional refractive optics. Alternatively, distributed aperture imaging can achieve comparable resolution in an essentially two-dimensional form factor by use of a number of smaller subapertures through which the image is interferometrically synthesized. The novelty of our approach lies in the optical upconversion of the mmW radiation as sidebands on carrier laser beams using electro-optic modulators. These sidebands are subsequently stripped from the carrier using narrow passband optical filters and a spatial Fourier transform is performed by means of a simple lens to synthesize the image, which is then viewed using a standard near-infrared focal plane array (FPA). Consequently, the optical configuration of the back-end processor represents a major design concern for the imaging system. As such, in this paper we discuss the optical configuration along with some of the design challenges and present preliminary imaging data validating the system performance.
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Thomas E. Dillon, Thomas E. Dillon, Christopher A. Schuetz, Christopher A. Schuetz, Richard D. Martin, Richard D. Martin, E. Lee Stein, E. Lee Stein, Jesse P. Samluk, Jesse P. Samluk, Daniel G. Mackrides, Daniel G. Mackrides, Mark S. Mirotznik, Mark S. Mirotznik, Dennis W. Prather, Dennis W. Prather, } "Optical configuration of an upconverted millimeter-wave distributed aperture imaging system", Proc. SPIE 7485, Millimetre Wave and Terahertz Sensors and Technology II, 74850G (24 September 2009); doi: 10.1117/12.830493; https://doi.org/10.1117/12.830493
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