Design of the freeform imaging system with large field of view and large relative aperture

Bingxu Chen; Zhiyuan Liao; Chao Cao; Yu Bai; Da Mu

doi:10.3788/IRLA20200005

Journals >Infrared and Laser Engineering >Volume 49 >Issue 8 >Page 20200005 > Article

Infrared and Laser Engineering
Vol. 49, Issue 8, 20200005 (2020)

Design of the freeform imaging system with large field of view and large relative aperture

Bingxu Chen¹, Zhiyuan Liao², Chao Cao², Yu Bai², and Da Mu¹

Author Affiliations

¹School of Opto-Electronic Engineering, Changchun University of Science and Technology, Changchun 130022, China

²Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China

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DOI: 10.3788/IRLA20200005 Cite this Article

Bingxu Chen, Zhiyuan Liao, Chao Cao, Yu Bai, Da Mu. Design of the freeform imaging system with large field of view and large relative aperture[J]. Infrared and Laser Engineering, 2020, 49(8): 20200005 Copy Citation Text

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Abstract

In recent years, freeform surfaces have been used increasingly in off-axis reflective imaging systems with high performance levels. In this paper, the cooled off-axis reflection optical system with both a large FOV(field-of-view) and a large relative aperture was designed based on the initial structure from vector aberration theory and genetic algorithm, by using a biased input field and an offset aperture stop, utilizing freeform surfaces described byXY polynomials to increase degrees of freedom to correct off-axis aberrations. The working band of the system was LWIR(long wavelength infrared) 8-12 μm, the focal length was 400 mm, the F-number was 2, the FOV was

$ 8^{\circ} \times 5^{\circ} $

, and the average root mean square (RMS) wavefront error of the system was 0.037 054λ(λ=9 μm).The detector''s cold stop matches the exit pupil of the optical system which ensure a 100% efficiency of the cold diaphragm. The system has a high energy concentration and a good image quality.

Keywords

freeform imaging system large field of view large relative aperture matching of cold stop

${H_{Aj}} = H - {\sigma _j}$

(1)

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${\rho ^{'}} = B\rho + {P_1}$

(2)

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$\left\{ \begin{aligned} W =& {\displaystyle \sum\limits_{{j}} {{W_{040j}}\left( {{\rho ^{'}} \cdot {\rho ^{'}}} \right)} ^2} + \displaystyle \sum\limits_j {{W_{131j}}\left( {H \cdot {\rho ^{'}}} \right) \times \left( {{\rho ^{'}} \cdot {\rho ^{'}}} \right)} +\\ & \dfrac{1}{2}\displaystyle \sum\limits_j {{W_{222j}}\left( {{H^2} \cdot {\rho ^{'}}^2} \right)} {\rm{ + }}\displaystyle \sum\limits_{{j}} {{W_{220Mj}}\left( {H \cdot H} \right)\left( {{\rho ^{'}} \cdot {\rho ^{'}}} \right)} +\\ & \displaystyle \sum\limits_j {{W_{131j}}\left( {H \cdot H} \right)\left( {{\rho ^{'}} \cdot {\rho ^{'}}} \right)} \\ & {W_{220Mj}} = {W_{220j}} + \dfrac{1}{2}{W_{222j}} \end{aligned} \right.$

(3)

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$\begin{split} & {{C}_{1}}={{B}^{4}}\displaystyle \sum\limits_{j}{{{W}_{040j}}} \\ & {{C}_{2}}={{B}^{3}}\left( 4\sum\limits_{j}{{{W}_{040j}}{{P}_{1}}+\displaystyle \sum\limits_{j}{{{W}_{131j}}{{H}_{Aj}}}} \right) \\ & {{C}_{3}}={{B}^{2}}\left( 2\sum\limits_{j}{{{W}_{040j}}{{P}_{1}}^{2}+\displaystyle \sum\limits_{j}{{{W}_{131j}}{{P}_{1}}{{H}_{Aj}}}} \right.\left. +\dfrac{1}{2}\displaystyle \sum\limits_{j}{{{W}_{222j}}{{H}^{2}}_{Aj}} \right) \\ & {{C}_{4}}={{B}^{2}}\left( 4\displaystyle \sum\limits_{j}{{{W}_{040j}}\left( {{P}_{1}}\centerdot {{P}_{1}} \right)+2\displaystyle \sum\limits_{j}{{{W}_{131j}}\left( {{P}_{1}}\centerdot {{H}_{Aj}} \right)}} \right.\left. +\displaystyle \sum\limits_{j}{{{W}_{220Mj}}\left( {{H}_{Aj}}\centerdot {{H}_{Aj}} \right)} \right) \\ & {{C}_{5}}=B\left( 4\sum\limits_{j}{{{W}_{040j}}\left( {{P}_{1}}\centerdot {{P}_{1}} \right){{P}_{1}}+2\displaystyle \sum\limits_{j}{{{W}_{131j}}\left( {{P}_{1}}\centerdot {{P}_{1}} \right){{H}_{Aj}}}} \right.+\displaystyle \sum\limits_{j}{{{W}_{131j}}{{P}_{1}}^{2}{{H}^{*}}_{Aj}} \;+\\ & \quad\;\;\left.\displaystyle \sum\limits_{j}{{{W}_{222j}}{{H}^{2}}_{Aj}{{P}_{1}}^{*}}+2\sum\limits_{j}{{{W}_{220Mj}}\left( {{H}_{Aj}}\centerdot {{H}_{Aj}} \right){{P}_{1}}+}\displaystyle \sum\limits_{j}{{{W}_{311j}}\left( {{H}_{Aj}}\centerdot {{H}_{Aj}} \right){{H}_{Aj}}} \right) \end{split}$

(4)

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$ \left\{ \begin{aligned} & Q = \displaystyle \int\limits_{\rm{c}}^d {\int\limits_a^b {Q\left( H \right){\rm d}{H_x}{H_y}\left( {a \leqslant {H_x} \leqslant b,c \leqslant {H_y} \leqslant d} \right)} } \\ & Q\left( H \right) = {\omega _1}\left| {{C_1}} \right| + {\omega _2}{\left\| {{C_2}} \right\|_1} + {\omega _3}{\left\| {{C_3}} \right\|_1} + {\omega _4}\left| {{C_4}} \right| + {\omega _5}{\left\| {{C_5}} \right\|_1} \end{aligned} \right. $

(5)

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