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Abstract
To realize a triple-views aerial image floating in the center of the passages that can be displayed in front of an user and passed through, we propose a novel display device using aerial imaging with retro-reflection with polarization. We confirmed that our device can form aerial images in the center of the intersection of three passages and can display different contents to users in each passage without using the material as screen.
© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
With the spread of large displays, information boards and signboards in towns are being rapidly replaced by digital signage in recent years. Because the contents of these display are easy to update, and because they can show movies and interactive contents, they are utilized in the field such as advertisements, timetables and guides. For example, if the information about the ways to multiple destinations are shown in front of the user on the flow line of their movement, its greater convenience can be expected. However, the disadvantage of large displays is that they take up a lot of space. Installing multiple large displays in the center of a high-traffic place such as an intersection obstructs traffic, and also presents the risk that users hit against the display.
What is expected to solve such problems is walk-through display. As a previous study of the image presentation technology without screen or with the scarce existence of a screen, a fog display, in which an image is projected on the artificially generated fog, has been proposed [1,2]. The method of projecting image on the smoke [3], and on the glass beads [4] can be used on the same purpose. In order to realize a guide image with (1) being installable in the center of the passages, (2) being displayed in front of user and passed through, and (3) presenting different contents for each passage, we focused on the method of aerial imaging by retro-reflection (AIRR, [5]). AIRR can make the floating image in the air without material screen, and the image has no physical restrictions, thus we can pass through it. In this paper, we propose a display device that can present different aerial floating images to three viewpoints that shifts by 120 degrees (Fig. 1).
2. Principle
Figure 2 explains the principle of aerial imaging by retro-reflection with polarization (p-AIRR, [6]). Of the light emitted from the light source, the s-polarized light component is reflected by the reflective polarizer and heads toward the retro-reflector. On the retro-reflector, λ/4 film is located. Since the light passes through the film twice before and after the retro-reflection, the plane of polarization is rotated 90 degrees, and then the light passes through the reflective polarizer. As a result, an aerial image is formed at the plane-symmetrical position to the light source with respect to the reflective polarizer.
Figure 3 is the diagram of our proposed device using p-AIRR. Our device has a triangular shape, and is cut at the corners to form passages. Reflective polarizer and retro-reflector with quarter-wave retarder film are placed inside, and light source is placed along the wall of the device. In this diagram, the length of this device, the width of light source, the width of the opening on the wall where the light pass, and the width of aerial image are defined as L (mm), D (mm), W (mm), and A (mm), respectively. The size of aerial image is dependent of both size of light source and the opening, thus
The retro-reflector is rotated by an angle θ (deg.) for the purpose of preventing its surface reflection. The aerial image is formed at the center of gravity of the same size triangle adjacent this device. Users can see the aerial image from only the position front of the device where users can see reflective polarizer and retro-reflector overlapping. Therefore, all or part of aerial image can be seen at the area painted in red in Fig. 3(b).
Fig. 3. Diagrams of our proposed triangular device seen from above. (a) Aerial image is formed at the center of gravity of adjacent triangle. Light path emitted from the light course is described as blue lines. (b) Aerial image can be seen from the viewpoint painted red.
By arranging this triangular device by rotating it by 120 degrees, three aerial images can be formed at the central position surrounded by the devices (Fig. 4). This area surrounded by devices is considered to be the intersection of passages shown in Fig. 1. Users walking down each passage will see one of three aerial images, for example, the user on passage A can see only the aerial image 1 formed by light source 1. To examine whether these devices present different contents for each passage and the aerial images projected towards other passages are not visible, the different pictures are displayed for each light source. Considering the whole area where users can see the aerial image of this device (Fig. 3(b)), it is appeared that the user at the area painted deep red in Fig. 4 can see two aerial images. The area where three aerial images can be seen at the same time was not confirmed. However, how the aerial image is actually seen depends on the scale of this device and the viewpoint of users.
Fig. 4. Layout of three triangular devices. The passages in Fig. 1 are overlapped at the central space surrounded by the devices. AI is abbreviation of Aerial image. The area painted red is where the aerial image can be seen.
Figure 5 explains how the aerial image is actually seen when the device is made so that the length of the one side of its triangle is 320 mm. Namely, parameters at Fig. 3(a) are L=320 mm, θ=15 deg, and D = W=A=105 mm. Interocular distance is set to 68 mm. The eye width is 34 mm. The user position is 200 mm away from the aerial image. In this case, the user can see almost the entire area of the aerial image, when the image is viewed from its front. In this study, we actually assembled a device on this scale, and examined whether this device can present a different aerial images in three directions at the same time.
Fig. 5. Range of aerial image within the user’s field of view. The aerial image can be seen at the viewpoint where retro-reflector and reflective polarizer overlap.
3. Experimental device and results
3.1 Experimental device
Figure 6 is a photograph of a device assembled on a scale of 320 mm on a side, namely, parameters at Fig. 3(a) is L=320, θ=15, D, W, A=105. This device was made of transparent acrylic boards with 5 mm thickness. For ease of producing and installing the device, its triangular corners was not cut off. Instead, the wall other than the opening for light passing are covered with a black rubber plate. SONY Xperia Z5 (light source 1 and 2, display area: 5.2 inch, brightness: 620 cd/m2) and XZs (light source 3, display area: 5.2 inch, brightness: 520 cd/m2) were used as the light source. The retro-reflector was RF-Ax of Nippon Carbide industries, and was rotated by 15 degrees horizontally and vertically to remove the mirror image of aerial image on itself [7]. To prevent light from the display reaching the user directly, a polarizer was placed on the display in a cross Nicol arrangement with reflective polarizer. And to prevent extra reflection of light inside the device, black rubber plates were attached to the walls and floor where the light passed.
3.2 Results
Figure 7 is a photograph of the aerial image formed by a triangular device. This photo was taken by NIKON D5500 (f/6.3, shutter speed: 1/80, ISO-2500) under the room light. The clear aerial image of the picture displayed on the light source could be seen. From the user, the light source and the mirror image of aerial image were not visible.
The position of formed aerial image was confirmed by using a screen (Fig. 8). In agreement with the principle, the aerial image was formed in the front of the device, with popping-up from its wall. No image was not formed on the screen when the screen was positioned in front of and behind the imaging position.
Fig. 8. Confirmation of the position of aerial image by using screen. (a) The screen is placed behind the imaging position. (b)The screen is placed at the position where the aerial image is formed. (c) The screen is placed in front of the imaging position (see Visualization 2).
Figure 9 shows photographs taken from each passage when three triangular devices were arranged and all light source displayed pictures at the same time. These photos were also taken under the room light. The brightness of aerial image depends on the one of the light source. Images in Figs. 9(a) and (b) were brighter than the image in Fig. 9(c), due to the difference of brightness of light source. At all passages, only one clear image was seen, and aerial images of pictures displayed on other light sources were not confirmed.
Fig. 9. Photographs of aerial images seen from each passage. (a), (b) and (c) are taken from passage A, B and C in Fig. 4, respectively.
4. Discussion
In Fig. 10, how aerial images can be seen when our principle is installed in the life-size passage is considered. The parameters at Fig. 3(a) were assumed as follows: L=6400 mm, θ=15 deg, and D = W=A=2100 mm. Passengers’ position are 2000 mm away from the aerial image formed at the intersection of passages. Under this condition, the user walking in the center of passage can see the central 50% of the aerial image. On the other hand, there seems to be little area of the aerial image that can be seen simultaneously by users walking on the right and left ends of the passage. Based on this analysis, it is difficult to form an aerial image so that its whole area (2.1m width) is visible for users in any position of the passage. However, the aerial image of the content displayed at the center 50% of the light source can be partially visible for users at both ends of the passage. By dividing the area of the light source into left and right sides and displaying the same information there, it is possible to provide equal information to users at the same time.
Furthermore, in Fig. 11, we analyzed the viewpoint at which two aerial images are visible for users on this scale. At the area painted deep red, when users are near to aerial images (User A in Fig. 11), their area visible for them will be enlarged, whereas it becomes difficult to see both aerial images at the same time because the angle to aerial images are also enlarged. When users are distant from aerial images (User B in Fig. 11), this angle becomes small, but users can see only a small part of the edge of each aerial image. Therefore, when our principle is installed in the life-size passage, it is unlikely that two aerial images will be in sight of users at the same time and confuse them.
Fig. 11. Analysis of visibility of each aerial image when users are at the area where two aerial images can be seen (painted deep red).
As the device is enlarged, it may be also necessary to examine materials of its components such as reflective polarizer [8]. Moreover, for the application of our principle to actual passage, the intensity of the light source should be increased to form bright aerial images. Although we used smart phones as the light sources, bright LED panel displays is suitable for large devices. The application of LED panel display is expected to increase of luminance of the aerial image near to 10 times.
5. Conclusion
To realize a triple-view aerial guide image in the center of the passages which can be displayed in front of user and passed through, we proposed the display device using aerial imaging by retro-reflection with polarization (p-AIRR). Our device has a triangular shape. Reflective polarizer and retro-reflector with quarter-wave retarder film are placed inside, and light source is placed along the wall of the device. These devices are arranged so that the intersection of three passages are surrounded by these three devices. When the different pictures are displayed on three light sources, only one clear aerial image of the picture displayed on the light source of the display device in front of the user was seen at each passage, and there aerial images of pictures displayed on other light sources were not confirmed. We were able to confirm that our proposed device can form the aerial floating image in the center of passage without no materials as screen, and we can pass through it, and we can display different information for each passage at the same time.
Funding
Japan Science and Technology Agency (JPMJAC1601).
Disclosures
The authors declare no conflicts of interest. This work is original and has not been published elsewhere.
References
1. I. Rakkolainen, S. DiVerdi, A. Olwal, N. Candussi, T. Hüllerer, M. Laitinen, M. Piirto, and K. Palovuori, “The interactive fogscreen,” ACM SIGGRAPH 2005 Emerging Technologies, Article No. 8 (2005).
2. A. Yagi, M. Imura, Y. Kuroda, and O. Oshiro, “360-degree fog projection interactive display,” SIGGRAPH Asia 2011 Emerging Technologies, Article No. 19 (2011).
3. T. Kusabuka and S. Eitoku, “Lucciola: Presenting Aerial Images by Generating a Fog Screen at any Point in the Same 3D Space as a User,” SA ‘19: SIGGRAPH Asia 2019 Posters, Article No. 38 (2019).
4. S. Ando, K. Otao, and Y. Ochiai, “Glass-Beads Display: Evaluation for Aerial Graphics Rendered by Retro-Reflective Particle,” HCI International 2019 Posters, 125–133 (2019).
5. H. Yamamoto, Y. Tomiyama, and S. Suyama, “Floating aerial LED signage based on aerial imaging by retro-reflection,” Opt. Express 22(22), 26919–26924 (2014). [CrossRef]
6. M. Nakajima, K. Onuki, I. Amimori, and H. Yamamoto, “Polarization State Analysis for Polarized Aerial Imaging by Retro-Reflection (PAIRR),” Proc. IDW 22, 429–432 (2015).
7. M. Yasugi and H. Yamamoto, “Forming Aerial Images at the Center of Triangular Container by Using Polarized Aerial Imaging by Retro-reflection (pAIRR),” Proc. IDW 25, 880–883 (2018). [CrossRef]
8. M. Yasugi, H. Yamamoto, and Y. Takeda, “Immersive aerial interface showing transparent floating screen between users and audience,” Proc. SPIE 11402, 114020O (2020). [CrossRef]
