A technology for eliminating stray light in optical readout of FPA

32 4 2013 8 J Infrared Millim Waves Vol 32No 4 August 2013 1001-9014201304 - 0331-06 DOI10 3724 /SP J 1010 2013 00331 * * 230027 CCD FPA FPA CCD 47% TN216 A A technology for eliminating stray light in optical readout of FPA ZHANG Zhi-GangMAO LiangCHENG Teng * ZHANG Qing-Chuan * CAS Key Laboratory of Mechanical Behavior and Design of Materials University of Science and Technology of ChinaHefei 230027China AbstractIn the uncooled optical readout infrared imaging technology based on knife edge filter the reflection of the optical elements bring in stray light spots in the CCD target surface It makes the proportion of FPA image in the detected light intensity signal reduced thus the sensitivity of optical detection is reduced A polarized optical readout system was proposed Polarizers and a quarter wave plate are added to the system The polarizing beam splitter is used to replace the original beam splitter The reflected stray light of the optical components in the optical path is thus eliminated The proportion of the FPA image received in the CCD target surface substantially increased so the optical detection sensitivity is enhanced The polarized optical readout infrared imaging experiment result showed that the detection sensitivity increased by about 47% than the non-polarized systemwhich is close to the theoretical value Key wordsoptical readoutuncooled infrared imagingpolarized lightquarter wave plate PACS07 05 Pj07 10 Cm07 57 -c07 60 Fs 2003 1-3 2012-04 -24 2012-10 -19 973 Received date2012-04 -24 revised date2012-10 -19 2011CB302105 11072233 11127201 11102201 WK2090050017 Foundation itemssupported by the State Key Development Program for Basic Research of China 2011CB302105 National Natural Science Foundation of China 11072233 11127201 11102201 and the Fundamental Research Funds for the Central Universities of Ministry of Education of China WK2090050017 Biography 1987- E-mailzzgang@ mail ustc edu cn * Corresponding author E-mailchteng@ ustc edu cn zhangqc@ ustc edu cn

332 32 FPA FPA FPA 1 4-7 FPA CCD CCD FPA FPA LED FPA CCD CCD 2 a LED b c d e f g FPA h i j k CCD Fig 2 Experimental setup a LED light sourceb pinholec beam splitterd Fourier transform lense glass window f vacuum chamberg FPAh germanium glass i infrared lens j Filter bladek CCD 1 Fig 1 Schematic of the infrared imaging system LED CCD CCD 3a CCD FPA FPA CCD CCD 3 b~ 3 CCD e CCD CCD FPA 3f 3b 3a FPA FPA CCD 3a 3 b FPA CCD 4 FPA a 3 c 3 b CCD 3b 1 1 1 CCD 12 bit CCD 0 4095 2 3c 4b 3d 3c CCD 3c 3d 2 LED 4 c 3 e 3 d

4 333 3 a bfpa 4 afpa b c c d d e f e fccd CCD Fig 4 aimage of FPA bimage of stray light caused by Fig 3 aimage w ith no shading bimage w ith shading betw een FPA and glass w indow cimage w ith shading glass window cimage of stray light caused by Fourier transform lens dimage of stray light caused beam splitter e betw een glass w indow and Fourier transform lens dimage w ith shading betw een Fourier transform lens and beam image of outside stray light fdc component of CCD background splitter eimage w ith LED light source offand fimage w ith shading in front of the CCD CCD 3d 3e 4 d 3 f 3 e CCD 3e 3f 4 e 3 e 3f 4e 4f 3f CCD CCD FPA ΔI /ΔT s CCD ΔI ΔT s 5 5 CCD Fig 5 components of CCD image 1 2 FPA ΔI = ΔT c Δθ ΔI Noise ΔT s ΔT s ΔT c Δθ = HS TΘ 2 Equivalent Temperature DifferenceNETD 2 H FPA NETD ΔT c ΔT s ΔT s S T FPA ΔI I noise Δθ ΔT c ΔT s Θ NETD = I ΔI Δθ noise 1 ΔI /ΔT s FPA L I noise CCD R CCD A λ

334 32 Ix f = Ux f = A2 R 8f 2 λ fl - Rx ( ) j π [ ] erf 1 2 - i 2 f 槡 Rλ fl - Rx ( ) j π [ ] + erf 1 2 - i 2 f 槡 Rλ = A 2 R /8f 2 λf erf x f 3 x f erf f 2 F erf 3 Θ 6 a~ c a bfpa ca b d~ f d Θ = d x knife efpa f dθ ( Ix f dx f ) = A 2 R/4fλF erf x knife 4 de - Fig 6 Image a~ cwere recorded when the CCD was dx f = 2fdθ x knife not supersaturated aimage with no shading bimage with shading between FPA and glass window cimage of - x knife subtraction of aand b image d~ fwere recorded Θ when the CCD was supersaturated dimage with no shading eimage with shading between FPA and glass window f image of subtraction of dand e 8 CCD FPA CCD 6 a CCD 2282 5 gray FPA CCD 7 6b 880 7gray 6c FPA 1401 8 gray 61 4% FPA FPA 0 6 d 2675 3 gray FPA 6 e 1015 4 gray 6 ffpa 7 a b c m d e f g h 1659 9 gray 61 9% i FPA j k l n CCD Fig 7 polarized light path a light sourceb pinholec FPA FPA window g vacuum chamberh quarter wave plate i FPA j germanium glassk infrared lens l filter bladen CCD 2 polaroidd polarizing beam splittere Fourier lens f glass CCD FPA 45 8a x FPA y

4 335 E = E o coswt + δ 0 5 E o w t δ 0 E x = E ox coswt 6 E x = E oy coswt 7 E ox = E oy = 槡 2 /2E o 8 Fig 8 Polarization when the light past the quarter wave plate CCD E' x = E ox coswt - 2π λ n ed 8 E' y = E oy coswt - 2π λ n od = E oy coswt - 2π λ n ed - δ o -e 9 n e n o λ d δ o -e = 2π λ n o - n e d 10 E y = E oy coswt - 2π λ n od 2 = E oy coswt - 2π λ n ed 2-2δ o -e = E oy coswt - 2π λ n ed 2 - π = - E oy coswt - 2π λ n ed 2= - E x 13 9a 2166 8 grayfpa CCD 9b 118 8 gray 9c 2048 0 gray 94 5% d n o - n e d = λ /4 δ o -e = π /2 9 a bfpa E' y = E oy sinwt - 2π λ n cab ed 11 Fig 9 Images a~ cwere recorded when the CCD was not supersaturated aimage with no shading bimage 8 11 with shading between FPA and the quarter wave plate cimage of subtraction of aand b 8b FPA 1 E x = E ox coswt - 2π FPA 94 λ n ed 2 12 5% FPA 1 46 FPA 46% 1 Table 1 Comparison of three modes /gray FPA /gray FPA /% 2282 5 1401 8 61 4 8c 2675 3 8a 2166 8 1659 9 2048 0 61 9 94 5 3 CCD CCD CCD 12 bit 10 CCD 11 FPA

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