31 March 2008 Liquid crystal tunable polarization filter for target detection applications
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Many natural materials produce polarization signatures, but man-made objects, typically having more planar or smoother surfaces, tend to produce relatively strong polarization signatures. These signatures, when used in combination with other means, can significantly aid in the detection of man-made objects. To explore the utility of polarization signatures for target detection applications we have developed a new type of polarimetric imaging sensor based on tunable liquid crystal components. Current state-of-the-art polarimetric sensors employ numerous types of imaging polarimeters, the most common of which are aperture division, micropolarizer, and rotating polarizer/analyzer. Our design uses an electronically tunable device that rotates the polarization of incoming light followed by a single fixed oriented linear polarizer. Its unique features include: 1) sub-millisecond response time switching speed, 2) ~75% transmission throughput, 3) no loss of sensor resolution, 4) zero mechanical moving parts, 5) broadband (~75% of center wavelength), 6) ~100:1 contrast ratio, 7) wide acceptance angle (±10°), and 8) compact and monolithic architecture (~10 inch3). This paper summarizes our tunable liquid crystal polarimetric imaging sensor architecture, benefits of our design, analysis of laboratory and field data, and the applicability of polarization signatures in target detection applications.
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Bruce Winker, Bruce Winker, Dong-Feng Gu, Dong-Feng Gu, Bing Wen, Bing Wen, Karen Zachery, Karen Zachery, John Mansell, John Mansell, Donald Taber, Donald Taber, Keith Sage, Keith Sage, William Gunning, William Gunning, Mario Aguilar, Mario Aguilar, } "Liquid crystal tunable polarization filter for target detection applications", Proc. SPIE 6972, Polarization: Measurement, Analysis, and Remote Sensing VIII, 697209 (31 March 2008); doi: 10.1117/12.779997; https://doi.org/10.1117/12.779997

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