Functional Projection Screen using Diverted Corner Cube Retroreflector (D-CCR) Tatsuo Uchida* , **, Ryosuke Ohtera*, Kazuhiro Wako*, Yumiko Ishitaka**, Mitsuru Kano**, K. Käläntär *** * National Institute of Technology, Sendai College, Sendai 981-1239, Japan ** Tohoku University, Sendai, 980-8579, Japan *** Global Optical Solutions, R&D Center, Tokyo 193-0832, Japan Keywords: Corner cube retroreflector; D-CCR; hollow CCR; directional screen; pillar; functional projection screen. ABSTRACT We devised and developed functional projection screen for personal use, small meetings, car pillars, and near eye projection. The screen deflects incident light from a projector by a fixed angle θview and diffuses in a certain angular range Δθview. We have realized the desired screen by modifying screen’s fine structures based on corner cube reflector (CCR) and reported basic concept and optical characteristics at IDW2017 and SID2018. In this paper, we report on further modification of the fine structures by changing the inclination angles and curvatures of three surfaces of the CCR that results in change of the diffused light pattern. Consequently we found out that the modification of basic deflection angle θview and the diffusion angle Δθview result in drastically change in screen characteristics. These new results were applied to optimization of the screen for personal use and car pillar applications. 1 INTRODUCTION Projection displays are one of the most growing markets. These displays are in small to large sizes and low to high luminance units. Nowadays small size projectors are more attractive for near-eye displays, wearable displays, small group meetings, personal use, automobile interior, and entertainments. Projection displays possess an image signal unit, controller, light source with optics, image engine with optics and a passive optical projection screen. In general a projection screen is a canvas cloth or a surface texture [1-6]. Variety of screens for front projection have been studied so far, such as matte white diffusive screens, pearl screens, silver screens, and retro screens. A matte screen is a Lambertian type [3-6]. These screens have wide viewing angles in which the reflection direction and light diffusion or the gain are approximately controlled. In addition, the gain of existing screens are 1-2.8 [6]. However, screens with higher gains for the aforementioned applications are absent in the market. In this study we intend to design a functional screen in order to control the direction of the reflected light as well as the diffusion pattern, i.e., viewing angle with high gain, for personal applications, and to preserve the luminous flux incident on the screen, in other words, to save the projector power consumption. 2 PROJECTION GEOMETRY 2.1 Conventional Projection Screen A conventional projection display schematically is shown in Fig.1. The projection is located at the overhead position of the viewer. The real image is projected on a white matte screen; i.e., a perfectly light diffusing characteristic with a gain of GҸ1 (Lambertian luminance distribution). A viewer is assumed to be in front of the screen. The luminance characteristics of a Lambertian screen and our screen, i.e., the objective of this study, are shown schematically in Fig.2 [1-6]. 2.2 Novel Projection Concept A functional screen reflects the incident light ray toward the viewer as shown in Fig.2(a). The position of a projector is fixed at overhead position of the viewer. The projected image (i.e., the light) is deflected toward the viewer, in which the reflected light is deviated from the projection direction by an angle of Tview. The reflected light is assumed to be scattered into an angle of 'Tview as shown in Fig.2(b). For comparison a Lambertian characteristics is shown in the figure. Here by definition the gain is the ratio of the luminance of our novel screen and that of the Lambertian, when both screens have the same surface area and incident luminous flux. 3 PROJECTION SCREEN USING D-CCR 3.1 Retroreflection Concept of CCR The optical concept of our functional screen is based on retroreflection characteristic of a CCR (corner cube reflector) [3-5]. The dihedral angles are 90q in an ordinary CCR. An incident ray on a CCR, after having three reflections on the inner surfaces of the CCR is directed toward the incident ray with opposite direction and having lateral shift depending on the CCR size [3-5,7,11]. In this paper, we use two coordinate systems, the xyz-system for CCR analyses, and XYZ-system for screen analyses on the aperture plane surface of the CCR (plane ABC). FMC3 - 2 ISSN-L 1883-2490/25/0432 © 2018 ITE and SID IDW ’18 432