Open Access
Add to BibSonomy
Abstract
Integral imaging three-dimensional (3D) display relies on display panel to provide visual information, but the intrinsic trade-off between the wide viewing angle and high resolution refrains its application in high-throughput 3D display. We propose a method to enhance the viewing angle without sacrificing the resolution by using two overlapped panels. The additionally introduced display panel is composed of two parts: the information area and the transparent area. The transparent area loaded with blank information enables light passing through without any modulation, while the opaque information area is loaded with element image array (EIA) for 3D display. The configuration of the introduced panel can block crosstalk from the original 3D display and establish a new and viewable perspective. Experimental results show that the horizontal viewing angle can be effectively extended from 8° to 16°, demonstrating the feasibility and effectiveness of our proposed method. This method provides the 3D display system with a higher space-bandwidth product, making it a potential technique to be applied for high information-capacity display, including integral imaging and holography.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Display technology represents a crucial medium for human perception and exploration of the world [1,2]. Naked-eye 3D display technologies, including light field 3D display [3–5], holographic 3D display [6,7] and volumetric 3D display [8,9], offer visual experiences that approach reality. Integral imaging is a form of light-field 3D display technology that employs uncomplicated and portable equipment to produce high-quality 3D image, while requiring relatively low amounts of data. This technique stems from integral photography that is first proposed by Lippmann in 1908, and relies on two processes: pickup and reconstruction [10]. During the pickup stage, the light field information of 3D object is recorded by means of a microlens array (MLA) to generate the element image array (EIA). In the reconstruction stage, the EIA is loaded onto a 2D display panel, and then the 3D object is reconstructed through MLA using the principle of optical reversibility [11,12]. Integral imaging provides authentic physical depth cues, accurate occlusion relationships and quasi-continuous viewpoints, delivering full-color 3D image without encountering the problem of vergence-accommodation conflict (VAC). Thus, it has emerged as a promising and attractive option for naked-eye 3D displays. However, the performance of integral imaging is restricted by the space-bandwidth product, which results in a narrow viewing angle, low resolution, shallow depth of field, and crosstalk.
Currently, research efforts in integral imaging are primarily focused on improving display performance. To enhance the viewing angle, one method is to implement curved structures, such as curved MLA or screens [13–15], which will rotate the sub optical axis of each lens. However, curved structures may introduce image distortion and compromise display quality. Another approach involves generating multiple viewing areas through time or spatial multiplexing, and subsequently stitching them together [16–20]. Techniques like dynamic moving MLA [21,22], backlight multiplexing [23], and head tracking [24] have been suggested. Regrettably, these methods may elevate system complexity and size, thus contradicting system portability. Furthermore, there exist techniques to optimize the optical parameters or layout of MLA [25–28], including the adoption of composite MLA [29,30], hexagonal MLA [31], or grating [32]. Nonetheless, these methods do not substantially improve the space-bandwidth product, and the overall information capacity of 3D display does not see a significant increase. Consequently, enhancing the viewing angle of integral imaging 3D display system presents a challenging task, considering the trade-offs among system complexity, display quality, and performance parameters.
In this paper, we propose a method to enhance the viewing angle of integral imaging by utilizing two overlapped display panels. The method involves introducing an additional display panel that is placed between the original display panel and MLA of a conventional configuration. The position and division of the display area have been calculated, and the feasibility of proposed method has been confirmed by experiments. Our proposed method is straightforward, portable, and eliminates the need for time multiplexing, thereby reducing the expense and complexity associated with enhancing the viewing angle.
2. Method
The schematic diagram of proposed method is shown in Fig. 1. Two layers of display panel are placed overlapped and combined with a MLA. Display Panel I and MLA form the traditional display architecture, while Display Panel II is newly introduced. The information contents on both displays are set up separately and displayed simultaneously. The entire display area of Display Panel I is loaded with EIA for integral imaging, and crosstalk-free 3D image can be reproduced in the Viewing Area I via the modulation of MLA. Viewing Area I corresponds to a viewing angle that is already present in the traditional display structure, and crosstalk can be generated outside Viewing Area I. The display area of the Display Panel II is divided into the information area and the transmission area. The transmission area is loaded with blank information, enabling the light from Display Panel I to pass through to Viewing Area I. The information area is opaque and obstructs the light from Display Panel I to the area outside Viewing Area I, thereby suppressing crosstalk from Display Panel I. At the same time, the information area is loaded with EIA to generate 3D image in Viewing Area II. The combination of Display Panel I and Display Panel II allows for an enhanced viewing angle of integral imaging 3D display.
The principle of using two overlapped display panels to extend the viewing angle of integral imaging 3D display is shown in Fig. 2. Figure 2(a) demonstrates the process of conventional integral imaging. Loading EIA on the display panel, light from the display panel carries 3D display information, which can be reconstructed at the central depth plane (CDP) by modulation of MLA. 3D image will be viewed by the observer at a certain distance, which is defined as viewing distance. At the viewing distance, the maximum area where a complete 3D image without crosstalk can be observed is called the viewing area, and the angle of the viewing area to MLA is defined as the viewing angle. Outside the viewing angle or viewing area, crosstalk image is generated. When the center of the display panel coincides with the center of MLA, the viewing area is the largest and directly opposite to MLA. After offsetting MLA by a distance relative to the display panel, the viewing area undergoes a corresponding displacement and reduction, as shown in Fig. 2(b). The maximum distance of MLA's offset is restricted to half the size of a single lens, and the resulting reduction in the viewing area is deemed negligible. Crosstalk occurs outside the viewing area.
Fig. 2. Principle of proposed method. (a) Traditional display. (b) After MLA offset. (c) Use Display Panel II to block the crosstalk. (b) Two display panels display simultaneously.
Display Panel II is placed intermediate to Display Panel I and the MLA, as demonstrated in Fig. 2(c). The display area of Display Panel II is set to transmit periodically, generating a periodic mask. This configuration serves as an aperture stop for each element image (EI) loaded on Display Panel I, permitting light from each EI to pass through its corresponding lens unit while preventing it from entering adjacent lens units. As a result, the light within the viewing area associated with Display Panel I remains unaffected and the crosstalk is suppressed. As shown in Fig. 2(d), the non-transparent region of Display Panel II loads a set of EIA for 3D display. The area on Display Panel II that does not pass through and loaded with display information is referred to as the information area, while the area that transmits light is termed the transparent area. The information area and the transmission area are interleaved, periodic, and each comprise the same units. The light emitted from the information area, modulated by MLA, can generate an additional viewing area outside the viewing area of Display Panel I. Let the viewing area corresponding to Display Panel I be denoted as Viewing Area I, and the corresponding area for Display Panel II be Viewing Area II. Thus, the method transforms the original crosstalk area of Display Panel I into a viewing area that is available for the observer, and the display information is provided by the information area of Display Panel II. Viewing Area I and Viewing Area II are combined, which improves the viewing area. The angle between the viewing area and the center of the lens plane is the viewing angle. Viewing Area I corresponds to the original viewing angle, while Viewing Area II corresponds to the increased viewing angle. The combination of two viewing angles forms the enhanced viewing angle. The enhancement of viewing angle means that observers can see 3D objects without crosstalk over a larger area range. The two-layer display method introduces fresh display information to the integral imaging system, and accomplishes an expanded viewing angle for integral imaging 3D display.
In conventional integral imaging system, the EI size and lens pitch are matched, as shown in Fig. 3(a). The viewing angle in theory, viewing area and actual viewing angle can be expressed as follows:
where ${p_{EI}}$ is the size of a single EI. g denotes to the distance from Display Panel to MLA.${p_L}$ is the lens pitch. L is the viewing distance. N is the number of lens units. The actual viewing angle and viewing area available for observer are limited and narrow.Fig. 3. Parameter analysis. (a) Lens pitch and EI size match. (b) Lens pitch and EI size do not match.
The viewing angle and viewing area can be enlarged by using the non-matching EI [33], as shown in Fig. 3(b). When the EI size is larger than the single lens pitch, the area available for human viewing is larger. The EI size in non-matching structure can be expressed as follows:
the actual viewing area and viewing angle and can be expressed as follows:Based on the structure using the non-matching EI, Display Panel II is introduced, as shown in Fig. 4. The entire area of Display Panel I loads EIA, and the area of Display Panel II is set to the transparent area and the information area. The EI size in Display Panel I can be expressed according to Eq. (4):
where ${g_1}$ denotes to the distance from Display Panel I to MLA. The length of the transparent area unit in Display Panel II can be expressed as:When the center of the combined viewing area coincides with the center of the lens, the corresponding viewing angle can be expressed as:
Once the parameters of the lens array have been determined, the EI size of EIA on Display Panel I depends on the viewing distance and the distance between Display Panel I and MLA. Additionally, the distance between Display Panel II and MLA decides the proportion of the transparent and information areas, and consequently, the dimensions of Viewing Area II, as illustrated in Fig. 5. If the transparent area on Display Panel II is excessive, the display information area will be constricted, causing a trade-off between transparent and information area division. Therefore, the distance between Display Panel II and MLA ought to be selected from the red line box in Fig. 5(a). Figure 5(b) portrays that the size of Viewing Area II is subject to the distance between Display Panel II and MLA.
Fig. 5. (a) Variation tendency of the size of the transmission area unit and information area unit when the distance from Display Panel II to MLA changed from 5 to 35 mm. (b) Variation tendency of the size of Viewing Area I and Viewing Area II when the distance from Display Panel II to MLA changed from 10 to 30 mm.
If both display panels share identical specifications, Display Panel II need to load blank information to allow the transmission of light from Display Panel I. Consequently, the amount of information accessible for the display of 3D image on Display Panel II is restricted by the size of information area, and is inferior to the overall volume of data on Display Panel I. In the proposed method, the display of 3D image in Viewing Area II will be slightly inferior to that of Viewing Area I. For instance, if the scale of Viewing Area I and Viewing Area II are comparable, the resolution of 3D images within Viewing Area II will be modestly worse. Alternatively, the supplementary viewing angle relative to Viewing Area II will be restricted in comparison to the original viewing angle applicable to Viewing Area I.
In the case of resolution priority, the combination of each layer of the display panel and MLA can generate two display modes: real image mode and virtual image mode, resulting in a total of four display mode combinations. If Display Panel I and Display Panel II simultaneously contribute to either the real or virtual image, achieving a comparable viewing angle to the original angle may prove challenging with a single MLA. In such instances, a set of MLA must be compensated, as shown in Fig. 6(a). The combination of the compensating MLA and the original MLA can actually be seen as a composite lens array, which will provide a new focal length for Display Panel I. However, when Display Panel I produces the real image and Display Panel II generates the virtual image, both images can be simultaneously displayed using a single lens array, allowing the added viewing angle comparable to the original viewing angle, as shown in Fig. 6(b).
Fig. 6. Different display modes. (a) Using compensate MLA. (b) Display Panel I for real image and Display Panel II for virtual image.
In the proposed method for enhancing the viewing angle of integral imaging, the display performance in the added viewing angle is diminished relative to the original viewing angle, manifesting as reduced resolution or virtual imagery. In general, Display Panel II provides the system with more display information, thereby augmenting the total volume of data of the 3D display, and thus overriding the limitations of performance indicators. The proposed method enhances the viewing angle of integral imaging 3D display and improves the overall display performance.
3. Experimental results
The feasibility of the proposed method has been verified, and experimental setup is demonstrated, as shown in Fig. 7. Display Panel I is a liquid crystal display (LCD) screen with an integral backlight module. Display Panel II is an LCD panel without backlight. The two display panels have the same specifications. The size is 12.5 inches, the resolution is 3840 × 2160, the pixel density is 352 PPI, and the pixel size is 0.072 mm. The lens pitch of MLA is 7.47 mm, the focal length of each single lens is 29.5 mm, and the total number of lenses is 37 × 21. Table 1 shows the specifications of devices used in optical experiments.
Table 1. Configuration of experimental setup
Set the viewing distance L to 1 m, the distance between Display Panel I and MLA is 36 mm. Set the distance between Display Panel II and MLA to 17.7 mm. The information area of Display Panel II is responsible for the display in Viewing Area II. According to Eq. (7), the EI size of EIA loaded on Display Panel I is 7.74 mm, the resolution of a single EI is 108 × 108. From Eq. (8) and Eq. (9), the size of the transmission area unit on Display Panel II is 3.8 mm, and the size of the information area unit is 3.8 mm. So the size of a single EI in EIA loaded on Display Panel II is 7.6 mm, and the resolution is 106 × 106. Setting the 3.8 mm area in the center of each EI as the information area, and the rest areas as the transparent area. Figure 8 shows the EIAs loaded on Display Panel I and Display Panel II respectively.
In the experiment, in order to make the display content in both viewing areas have high resolution, the display modes of two display panels are set respectively. Display Panel I is responsible for the original viewing angle corresponding to Viewing Area I, demonstrating real image. Display Panel II is in charge of the added viewing angle relative to Viewing Area II, contributing to virtual image. The size of Viewing Area II is equivalent to Viewing Area I. In order to make it easier to distinguish the newly added Viewing Area II from the original Viewing Area I, and to demonstrate the expansion of the viewing area and viewing angle, the same model with different colors is used when recording two sets of EIA. The model recorded in Display Panel I is a bone with a blue intervertebral disc, and the model recorded by in Display Panel II is a bone with a pink intervertebral disc. The experimental results are shown in Fig. 9.
Fig. 9. Experiment results. (a) Real image display under traditional display structure. (b) The crosstalk of the real image is suppressed. (c) The display of proposed method.
Figure 9(a) shows the 3D display results of only turning on Display Panel I, which can be considered as the control group, and EIA is loaded. At the viewing distance, the viewing angle of the 3D image reconstructed ranges from −8 ° to 0 °. From 0 ° to 8 ° outside the viewing angle, it is crosstalk image, and the effective viewing angle is 8 °.
As shown in Fig. 9(b), Display Panel I and Display Panel II are both turned on. The information area of Display Panel II is set to be black, and the transmission area is transparent, forming a periodic occlusion. From −8 ° to 0 °, the reconstructed 3D image is not affected, while the crosstalk from 0° to 8° is suppressed.
Figure 9(c) shows the 3D display result when EIA the information area of Display Panel II is loaded with EIA, while Display Panel I is also turned on. Display Panel I shows the real image of blue striped bone from −8° to 0° angle of view. At the angle of 0 ° to −8 °, the virtual image of the pink striped bone is displayed. The overall final horizontal viewing angle is 16 °, twice the display result of just turning on Display Panel I. The experimental results demonstrate that the proposed method of extending the viewing angle of integral imaging 3D display with two overlapped display panels is effective and feasible.
The experimental results show that the method of using two overlapped display panels can be utilized to enhance the viewing angle of integral imaging 3D display. By introducing an additional display panel, the crosstalk area under the traditional structure is converted into another viewing area. However, the current presentation system has several limitations. Since Display Panel II is an LCD panel, its internal structure weakens the intensity to the transmitted light, which may lead to a decrease in the brightness of the real image displayed by Display Panel I. At the same time, the backlight of Display Panel II comes from Display Panel I. The backlight is not pure white light, which carries the intensity information of Display Panel I, including the crosstalk. Part of the backlight intensity will be blocked by the black area in the EIA loaded on information area, while the other part will be modulated by the color area through RGB channels. This allows the information area of Display Panel II to display as its loaded EIA, but with some interference due to the backlight not being pure white. As a result, partial shadows exist in the virtual 3D image that Display Panel II is responsible for. To overcome such a problem, error compensation for the information area of Display Panel II should be considered. Also, a transparent OLED can serve as Display Panel II, and such a structure will further improve the overall display quality. In our future work, composite MLA and multiple layers of display will be used to achieve integral imaging 3D display with higher performance.
4. Conclusion
In this paper, we propose a method to enhance the viewing angle of integral imaging by employing two overlapped display panels. To achieve this, an extra display panel is introduced to the traditional structure, which is divided into information and transparent areas. This division effectively suppresses crosstalk outside the original viewing angle and offers an additional observable viewing angle. Our experiments provide an enhanced viewing angle of 16°, twice the original 8° viewing angle, demonstrating the viability of the method. Due to the expanded space-bandwidth product, our method increases the total volume of information accessible for 3D display, bypassing the restrictive relationship between the wide viewing angle and high resolution. Additionally, the two-layer display panel structure may be expanded to multiple layers, enabling improvements for other display performances. Our method is potentially applicable in various 3D display systems, including integral imaging, multi-view display, and holography.
Funding
National Key Research and Development Program of China (2021YFB2802300); National Natural Science Foundation of China (NSFC), (61975014, 62035003, U22A2079); Beijing Municipal Science & Technology Commission, Administrative Commission of Zhongguancun Science Park (Z211100004821012).
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. J. Geng, “Three-dimensional display technologies,” Adv. Opt. Photonics 5(4), 456–535 (2013). [CrossRef]
2. J. Hong, Y. Kim, H.-J. Choi, J. Hahn, J.-H. Park, H. Kim, S.-W. Min, N. Chen, and B. Lee, “Three-dimensional display technologies of recent interest: principles, status, and issues [Invited],” Appl. Opt. 50(34), H87–H115 (2011). [CrossRef]
3. X. Guo, X. Sang, B. Yan, H. Wang, X. Ye, S. Chen, H. Wan, N. Li, Z. Zeng, D. Chen, P. Wang, and S. Xing, “Real-time dense-view imaging for three-dimensional light-field display based on image color calibration and self-supervised view synthesis,” Opt. Express 30(12), 22260–22276 (2022). [CrossRef]
4. X. Guo, X. Sang, D. Chen, P. Wang, H. Wang, X. Liu, Y. Li, S. Xing, and B. Yan, “Real-time optical reconstruction for a three-dimensional light-field display based on path-tracing and CNN super-resolution,” Opt. Express 29(23), 37862–37876 (2021). [CrossRef]
5. X. Su, X. Yu, D. Chen, H. Li, X. Gao, X. Sang, X. Pei, X. Xie, Y. Wang, and B. Yan, “Regional selection-based pre-correction of lens aberrations for light-field displays,” Opt. Commun. 505, 127510 (2022). [CrossRef]
6. D. Pi, J. Wang, J. Liu, J. Li, Y. Sun, Y. Yang, W. Zhao, and Y. Wang, “Color dynamic holographic display based on complex amplitude modulation with bandwidth constraint strategy,” Opt. Lett. 47(17), 4379–4382 (2022). [CrossRef]
7. H. Ma, C. Wei, J. Wei, Y. Han, D. Pi, Y. Yang, W. Zhao, Y. Wang, and J. Liu, “Superpixel-based sub-hologram method for real-time color three-dimensional holographic display with large size,” Opt. Express 30(17), 31287–31297 (2022). [CrossRef]
8. C. Blackwell, C. Can, J. Khan, X. Chen, and I. Underwood, “Volumetric 3D display in real space using a diffractive lens, fast projector, and polychromatic light source,” Opt. Lett. 44(19), 4901–4904 (2019). [CrossRef]
9. K. Kumagai, I. Yamaguchi, and Y. Hayasaki, “Three-dimensionally structured voxels for volumetric display,” Opt. Lett. 43(14), 3341–3344 (2018). [CrossRef]
10. X. Xiao, B. Javidi, M. Martinez-Corral, and A. Stern, “Advances in three-dimensional integral imaging: sensing, display, and applications [Invited],” Appl. Opt. 52(4), 546–560 (2013). [CrossRef]
11. Z. Zhao, J. Liu, L. Xu, Z. Zhang, and N. Zhao, “Wave-optics and spatial frequency analyses of integral imaging three-dimensional display systems,” J. Opt. Soc. Am. A 37(10), 1603–1613 (2020). [CrossRef]
12. N.-Q. Zhao, J. Liu, and Z.-F. Zhao, “High performance integral imaging 3D display using quarter-overlapped microlens arrays,” Opt. Lett. 46(17), 4240–4243 (2021). [CrossRef]
13. Y. Kim, J.-H. Park, H. Choi, S. Jung, S.-W. Min, and B. Lee, “Viewing-angle-enhanced integral imaging system using a curved lens array,” Opt. Express 12(3), 421–429 (2004). [CrossRef]
14. Y. Kim, J.-H. Park, S.-W. Min, S. Jung, H. Choi, and B. Lee, “Wide-viewing-angle integral three-dimensional imaging system by curving a screen and a lens array,” Appl. Opt. 44(4), 546–552 (2005). [CrossRef]
15. D.-H. Shin, B. Lee, and E.-S. Kim, “Multidirectional curved integral imaging with large depth by additional use of a large-aperture lens,” Appl. Opt. 45(28), 7375–7381 (2006). [CrossRef]
16. S. Jung, J.-H. Park, H. Choi, and B. Lee, “Viewing-angle-enhanced integral three-dimensional imaging along all directions without mechanical movement,” Opt. Express 11(12), 1346–1356 (2003). [CrossRef]
17. S.-W. Min, B. Javidi, and B. Lee, “Enhanced three-dimensional integral imaging system by use of double display devices,” Appl. Opt. 42(20), 4186–4195 (2003). [CrossRef]
18. G. Baasantseren, J.-H. Park, K.-C. Kwon, and N. Kim, “Viewing angle enhanced integral imaging display using two elemental image masks,” Opt. Express 17(16), 14405–14417 (2009). [CrossRef]
19. C.-W. Chen, M. Cho, Y.-P. Huang, and B. Javidi, “Improved Viewing Zones for Projection Type Integral Imaging 3D Display Using Adaptive Liquid Crystal Prism Array,” J. Display Technol. 10(3), 198–203 (2014). [CrossRef]
20. Y. Zhu, X. Sang, X. Yu, P. Wang, S. Xing, D. Chen, B. Yan, K. Wang, and C. Yu, “Wide field of view tabletop light field display based on piece-wise tracking and off-axis pickup,” Opt. Commun. 402, 41–46 (2017). [CrossRef]
21. B. Lee, S. Jung, and J.-H. Park, “Viewing-angle-enhanced integral imaging by lens switching,” Opt. Lett. 27(10), 818–820 (2002). [CrossRef]
22. H. Choi, S.-W. Min, S. Jung, J.-H. Park, and B. Lee, “Multiple-viewing-zone integral imaging using a dynamic barrier array for three-dimensional displays,” Opt. Express 11(8), 927–932 (2003). [CrossRef]
23. B. Liu, X. Sang, X. Yu, X. Gao, L. Liu, C. Gao, P. Wang, Y. Le, and J. Du, “Time-multiplexed light field display with 120-degree wide viewing angle,” Opt. Express 27(24), 35728–35739 (2019). [CrossRef]
24. Z.-L. Xiong, Q.-H. Wang, S.-L. Li, H. Deng, and C.-C. Ji, “Partially-overlapped viewing zone based integral imaging system with super wide viewing angle,” Opt. Express 22(19), 22268–22277 (2014). [CrossRef]
25. H. Kim, J. Hahn, and B. Lee, “The use of a negative index planoconcave lens array for wide-viewing angle integral imaging,” Opt. Express 16(26), 21865–21880 (2008). [CrossRef]
26. J.-Y. Jang, H.-S. Lee, S. Cha, and S.-H. Shin, “Viewing angle enhanced integral imaging display by using a high refractive index medium,” Appl. Opt. 50(7), B71–B76 (2011). [CrossRef]
27. X. Gao, X. Sang, W. Zhang, and B. Yan, “Viewing resolution and viewing angle enhanced tabletop 3D light field display based on voxel superimposition and collimated backlight,” Opt. Commun. 474, 126157 (2020). [CrossRef]
28. Y. Wang, X. Sang, S. Xing, X. Yu, X. Gao, B. Liu, C. Gao, L. Liu, R. Dai, and F. Ge, “Three-dimensional light-field display with enhanced horizontal viewing angle by introducing a new lenticular lens array,” Opt. Commun. 477, 126327 (2020). [CrossRef]
29. W. X. Wei Xie, Y. W. Yazhou Wang, H. D. Huan Deng, and Q. W. Qionghua Wang, “Viewing angle-enhanced integral imaging system using three lens arrays,” Chin. Opt. Lett. 12(1), 011101 (2014). [CrossRef]
30. L. Liu, X. Sang, X. Yu, X. Gao, Y. Wang, X. Pei, X. Xie, B. Fu, H. Dong, and B. Yan, “3D light-field display with an increased viewing angle and optimized viewpoint distribution based on a ladder compound lenticular lens unit,” Opt. Express 29(21), 34035–34050 (2021). [CrossRef]
31. Z.-F. Zhao, J. Liu, Z.-Q. Zhang, and L.-F. Xu, “Bionic-compound-eye structure for realizing a compact integral imaging 3D display in a cell phone with enhanced performance,” Opt. Lett. 45(6), 1491–1494 (2020). [CrossRef]
32. J. Hua, E. Hua, F. Zhou, J. Shi, C. Wang, H. Duan, Y. Hu, W. Qiao, and L. Chen, “Foveated glasses-free 3D display with ultrawide field of view via a large-scale 2D-metagrating complex,” Light: Sci. Appl. 10(1), 213 (2021). [CrossRef]
33. H. Deng, Q.-H. Wang, L. Li, and D.-H. Li, “An integral-imaging three-dimensional display with wide viewing angle,” J. Soc. Inf. Disp. 19(10), 679–684 (2011). [CrossRef]
