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Holographic optical element (HOE) lens is an imaging element fabricated through recording wavefront by interference. Because of its advantages of small form factor and wavelength, angle selectivity and arbitrary wavefront formation, it has a good application prospect in augmented reality display. To make the system more compact, the HOE lens is adopted as an off-axis optical element. At the same time, according to diffraction principle, its wavelength response is more sensitive than those of traditional refractive and reflective optical elements. Thus the fabrication and design of a full-color HOE lens is a challenge to optimizing the free-space head-up display system. To systematically analyze the HOE imaging system, the conjugate relation between the object and image is derived by scalar diffraction theory. Then the Gaussian conjugate imaging equation is obtained and the off-axis aberration of distortion and astigmatism in the HOE imaging system are analyzed. In addition, A head-up display with field of view (FOV) of 18° and eyebox of 10 mm is simulated and its imaging process is visualized through the geometric optics method of k -vector diagram and ray-tracing. A full-color HOE lens with high diffraction efficiency is fabricated by interference. Its average peak diffraction efficiency is 56.7%, reaching a high level in the world. A prototype of augmented reality system is established by integrating laser pico-projectior with HOE lens. The experimental results of distortion effect and astigmatism effect of the system are obtained, which are consistent with the simulation results. The modulation transfer function (MTF) parameter of the system is measured, and its definition basically meets the requirements of the human eyes for resolution. The aberration of the system is analyzed and the optimization method is proposed. To optimize the monochromatic image quality, an extra cylindrical lens is added to ensure the same optical power of meridian and sagittal plane to eliminate the astigmatism. Besides, a freeform wavefront is designed by the geometric construction method and forms a freeform HOE to deal with the distortion problem. The local recording freeform wavefront can be calculated by the imaging equation. When full-color HOE is applied to the display system, the images of three channels may separate in the space because of their different reconstruction wavelengths and angles. We propose a pre-compensation method of recording process to solve this problem. If these above-mentioned problems can be solved, due to its good image uniformity, sufficient field angle and eyebox area, the head-up display based on HOE lens with extra optical power will have a better application in augmented reality technology.
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Keywords:
- holographic optical element /
- laser display /
- near-eye display /
- augmented reality
[1] Xiong J, Hsiang E L, He Z, Zhan T, Wu S T 2021 Light: Sci. Appl. 10 216
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[2] Zhan T, Yin K, Xiong J, He Z, Wu S T 2020 iScience 23 101397
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[3] 史晓刚, 薛正辉, 李会会, 王丙杰, 李双龙 2021 中国光学 14 1146
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Shi X G, Xue Z H, Li H H, Wang B J, Li S L 2021 Chin. Opt. 14 1146
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[4] Yu C, Peng Y F, Zhao Q, Li H F, Liu X 2017 Appl. Opt. 56 9390
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[5] Han J, Liu J, Yao X C, Wang Y T 2015 Opt. Express 23 3534
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[6] 金闻嘉 2020 硕士学位论文 (杭州: 浙江大学)
Jin W J 2020 M S. Dissertation (Hangzhou: Zhejiang University) (in Chinese)
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[10] 刘奡 2019 博士学位论文 (南京: 东南大学)
Liu A 2019 Ph. D. Dissertation (Nanjing: Dongnan University) (in Chinese)
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Google Scholar
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Google Scholar
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图 1 光波导AR显示系统原理示意图
Figure 1. Schematic diagram of optical waveguide AR display system principle.
图 2 自由空间光学组合器AR显示系统示意图
Figure 2. Schematic diagram of free-space optical combiner AR display system.
图 3 全息透镜记录波前示意图
Figure 3. Schematic diagram of the recording wavefront of an HOE lens.
图 4 单片全息透镜的成像原理图, 红、绿和蓝线分别为不同视场的物光线(图中FOV为视场角; HOEL为全息透镜)
Figure 4. Principle diagram of the imaging process of a singlet HOE lens and the red, green and blue rays are the object rays with different fields of view. (FOV represents the field of view and HOEL represents the holographic optical element lens)
图 5 HOE的波前k矢量图 (a)记录过程; (b)再现过程
Figure 5. k-vector diagram of an HOE: (a) Recording process; (b) reconstruction process.
图 6 光线追迹的方式模拟成像效果 (a)子午面xz; (b)弧矢面yz
Figure 6. Simulation of the imaging process through ray-tracing: (a) Meridian plane xz; (b) sagittal plane yz.
图 7 全色全息透镜AR系统示意图(SLM, 空间光调制器; HOEL, 全息透镜)
Figure 7. Schematic diagram of full-color AR system based on an HOE lens (SLM, a spatial light modulator; HOEL, holographic optical element lens).
图 8 全色全息透镜的制作示意图
Figure 8. Schematic diagram for fabricating a full-color HOE lens.
图 9 投影型AR系统的原型
Figure 9. Prototype of projection-type AR system.
图 10 全色全息透镜成像的图像效果 (a)红光; (b)绿光; (c)蓝光
Figure 10. Image effect of full-color HOE lens: (a) Red light; (b) green light; (c) blue light..
图 11 RGB子光栅的角度选择性
Figure 11. Angular selectivity of the RGB sub-gratings.
图 12 全息透镜成像系统的MTF曲线测量
Figure 12. MTF curves measurement of HOE lens imaging system.
图 13 全息透镜的像散效果, 透镜聚焦于(a)子午像处和(b)弧矢像处
Figure 13. Astigmatic of the HOE lens, focusing on (a) meridian image and (b) sagittal image.
图 14 子午面和弧矢面的成像示意图 (a)子午面xz; (b)弧矢面yz
Figure 14. Imaging diagram of meridian plane and sagittal plane: (a) Meridian plane xz; (b) sagittal plane yz.
图 15 全息透镜的畸变效果
Figure 15. Distortion effect of HOE lens.
图 16 自由曲面HOE的几何构造设计方法示意图
Figure 16. Schematic diagram of geometric construction design method of freeform HOE.
图 17 不同子光栅的成像过程(其中红线、绿线分别为红光、绿光的成像过程, 青色线为物方光线)
Figure 17. Imaging process of different sub-grating (red line represents red light, green line represents green light and cyan line represents light from the object).
表 1 全息透镜成像系统的光学参数
Table 1. Optical parameters of HOE lens imaging system.
参数 数值 眼盒大小/mm 10 视场角/(°) 18 全息透镜焦距/mm 65 红、绿、蓝光栅角带宽/(°) 12 
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[1] Xiong J, Hsiang E L, He Z, Zhan T, Wu S T 2021 Light: Sci. Appl. 10 216
Google Scholar
[2] Zhan T, Yin K, Xiong J, He Z, Wu S T 2020 iScience 23 101397
Google Scholar
[3] 史晓刚, 薛正辉, 李会会, 王丙杰, 李双龙 2021 中国光学 14 1146
Google Scholar
Shi X G, Xue Z H, Li H H, Wang B J, Li S L 2021 Chin. Opt. 14 1146
Google Scholar
[4] Yu C, Peng Y F, Zhao Q, Li H F, Liu X 2017 Appl. Opt. 56 9390
Google Scholar
[5] Han J, Liu J, Yao X C, Wang Y T 2015 Opt. Express 23 3534
Google Scholar
[6] 金闻嘉 2020 硕士学位论文 (杭州: 浙江大学)
Jin W J 2020 M S. Dissertation (Hangzhou: Zhejiang University) (in Chinese)
[7] Peng H C, Cheng D W, Han J, Xu C, Song W T, Ha L Z, Yang J, Hu Q X, Wang Y T 2014 Appl. Opt. 53 H177
Google Scholar
[8] Li G, Lee D, Jeong Y, Cho J, Lee B 2016 Opt. Lett. 41 2486
Google Scholar
[9] Chang C, Bang K, Wetzstein G, Lee B, Gao L 2020 Optica 7 1563
Google Scholar
[10] 刘奡 2019 博士学位论文 (南京: 东南大学)
Liu A 2019 Ph. D. Dissertation (Nanjing: Dongnan University) (in Chinese)
[11] 邬融, 孙明营, 周申蕾, 乔战峰, 华能 2020 物理学报 69 234209
Google Scholar
Wu R, Sun M Y, Zhou S L, Qiao Z F, Hua N 2020 Acta Phys. Sin. 69 234209
Google Scholar
[12] Cheng D W, Wang Y T, Hua H, Talha M M 2009 Appl. Opt. 48 2655
Google Scholar
[13] Pulli K 2017 Sid Symposium Digest of Technical Papers 48 132
Google Scholar
[14] Li G, Jeong J, Lee D, Yeom J, Jang C, Lee S, Lee B 2015 Opt. Express 23 33170
Google Scholar
[15] Jang C G, Mercier O, Bang K, Li G, Zhao Y, Lanman D 2020 ACM Trans. Graph. 39 184
Google Scholar
[16] Maimone A, Wang J 2020 ACM Trans. Graph. 39 67
Google Scholar
[17] Jang C, Hong K, Yeom J, Lee B 2014 Opt. Express 22 27958
Google Scholar
[18] Jang C, Lee C K, Jeong J, Li G, Lee S, Yeom J, Hong K, Lee B 2016 Appl. Opt. 55 A71
Google Scholar
[19] Lee S, Lee B, Cho J, Jang C, Kim J, Lee B 2017 IEEE Photon. Technol. Lett. 29 82
Google Scholar
[20] Li Y N Q, Yang Q, Xiong J H, Yin K, Wu S T 2021 Opt. Express 29 42696
Google Scholar
[21] Xiong J, Yin K, Li K, Wu S T 2021 Adv. Photonics Res. 2 2000049
Google Scholar
[22] Xie Y, Kang M W, Wang B P 2014 Appl. Opt. 53 4206
Google Scholar
[23] Zhang Y N, Zhu X L, Liu A, Weng Y S, Shen Z W, Wang B P 2019 Appl. Opt. 58 G84
Google Scholar
[24] Shen Z W, Zhang Y N, Weng Y S, Li X H 2017 IEEE Photonics J 9 7000911
Google Scholar
[25] Piao J A, Li G, Piao M L, Kim N 2013 J. Opt. Soc. Korea. 17 242
Google Scholar
[26] Piao M L, Kim N 2014 Appl. Opt. 53 2180
Google Scholar
[27] Piao M L, Kwon K C, Kang H J, Lee K Y, Kim N 2015 Appl. Opt. 54 5252
Google Scholar
[28] Zhu J, Yang T, Jin G F 2013 Opt. Express 21 26080
Google Scholar
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