Design of Dual-Band Infrared Optical System with Q-type Asphere

Fig. 4. MTF curves of optical system with Q-type asphere. (a) MWIR at -40 ℃; (b) MWIR at 20 ℃; (c) MWIR at 60 ℃; (d) LWIR at -40 ℃; (e) LWIR at 20 ℃; (f) LWIR at 60 ℃

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Fig. 5. MTF curves of optical system with even asphere. (a) MWIR at -40 ℃; (b) MWIR at 20 ℃; (c) MWIR at 60 ℃; (d) LWIR at -40 ℃; (e) LWIR at 20 ℃; (f) LWIR at 60 ℃

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Fig. 6. Q-type aspherical surface

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Fig. 7. Deviation from the best fit sphere. (a) Q-type asphere; (b) even asphere

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Table 1. Main design parameters of optical system

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Table 1. Main design parameters of optical system

Parameter	Value
Wave band /μm	3-5 & 8-11
Effective focal length /mm	21
Filed of view /(°)	30
F number	2.6
Temperature range /℃	-40-60
MTF@20 (lp/mm)	>0.5@MWIR>0.3@LWIR
Distortion	<2%
Detector specification /(pixel×pixel)	320×320
Pixel size /(μm×μm)	25×25

Table 2. Main property parameters of two infrared materials
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Table 2. Main property parameters of two infrared materials
Material Refractive index TCRI @10 μm/K^-1 Spectral range /μm
λ=4 μm λ=10 μm
Ge 4.0243 4.0032 0.000396 2.0-17
IG4 2.6220 2.6090 0.000020 0.8-14

Table 3. RMS radius of optical system with Q-type asphere

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Table 3. RMS radius of optical system with Q-type asphere

FOV /(°)	RMS in MWIR /μm				RMS in LWIR /μm
FOV /(°)	-40 ℃	20 ℃		60 ℃	-40 ℃	20 ℃		60 ℃
0	5.672		4.318				6.985		12.468	9.923	5.768
5	4.863		5.650				8.741		11.498	8.101	4.023
10	5.741		9.404				12.079		9.238	4.572	3.399
15	7.646		9.248				11.624		10.982	7.359	5.612

Table 4. Parameters of Q-type asphere and even asphere

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Table 4. Parameters of Q-type asphere and even asphere

Parameter	Q-type asphere	Parameter	Even asphere
ρ_max /mm	8.6222	k /mm	-0.1850
ε /mm	0.7303	c /mm	0.0588
c /mm	0.0591	a₄ /mm	2.0047×10^-5
a₀ /mm	-0.1618	a₆ /mm	7.5247×10^-7
a₁ /mm	-0.2998	a₈ /mm	-3.5592×10^-8
a₂ /mm	-0.1856	a₁₀ /mm	9.0774×10^-10
a₃ /mm	-0.0704	a₁₂ /mm	4.3803×10^-12
a₄ /mm	-0.0151	a₁₄ /mm	-3.4455×10^-13
a₅ /mm	-1.1715×1 ${0^{-}}^{3}$

Table 5. RMS radius of optical system with even asphereμm

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Table 5. RMS radius of optical system with even asphereμm

FOV/(°)	RMS in MWIR				RMS in LWIR
FOV/(°)	-40 ℃	20 ℃		60 ℃	-40 ℃	20 ℃		60 ℃
0	3.934		6.693				10.163		12.291	7.422	2.891
5	4.613		7.856				11.285		11.495	5.912	3.140
10	6.158		10.049				13.437		9.617	4.841	4.010
15	8.222		9.546				11.836		12.725	8.415	7.676