Design of Optical Thin-Film Filters for Multispectral Palmprint Image Acquisition Systems

Fig. 7. Spectral curves after optimized superposition. (a) Double-sided cut-off depth curves; (b) transmittance curve of 520 nm filter; (c) cut-off depth curve of 520 nm filter

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Fig. 8. Spectral curve of transmittance of four-channel filter

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Table 1. Spectral characteristic parameters
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Table 1. Spectral characteristic parameters
Parameter Value
Permissible error ±2 nm
Transmittance >90%
Full width at half maximum 8--12 nm
Cut off range 400 nm-λ₁,λ₂-1100 nm
Cut off depth(except passband) >OD6

Table 2. Specific film indexes of 470 nm, 630 nm, and 880 nm filters

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Table 2. Specific film indexes of 470 nm, 630 nm, and 880 nm filters

Central wavelength /nm	470	630	880
Total number of film layers on side A	52	52	52
Total film thickness on side A /nm	5354.44	5872.63	6654.39
Total number of film layers on side B	97	97	97
Total film thickness on side B /nm	6087.41	6325.96	7032.42
Reference wavelength /nm	430,625,840	510,736,920	554,726,1000

Table 3. Spectral performance index of four channel filter
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Table 3. Spectral performance index of four channel filter
Central wavelength /nm 470 520 630 880
Transmittance /% 91.4 90.7 93.6 92.8
Full width at half maximum of passband /nm 9.7 10.8 11.4 11.7

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Zhiqiang Yu, Shuguo Fei, Shuaifeng Zhao, Zhishuai Guo. Design of Optical Thin-Film Filters for Multispectral Palmprint Image Acquisition Systems[J]. Acta Optica Sinica, 2021, 41(23): 2331001

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