[Paper] Autostereoscopic Displays with Time-multiplexed Directional Backlight Using Curved Lens Arrays

Abstract

Conventional works on autostereoscopic displays are mostly based either on parallax barrier or on lenticular lens, both of which have a drawback that the resolution of the provided image is lower than the original resolution of the LCD panel they use. For example, the image resolution becomes half of the panel resolution or less when a conventional passive barrier is applied. Time-division multiplexing technology can realize a view having the resolution equal to that of the panel. The active parallax barrier is a typical way to implement this method [1-8]. Alternating the odd and even columns of the striped barrier and synchronizing it with the image on the display panel, the viewers can see a full resolution stereoscopic image. Another way to attain this goal is to use a timemultiplexed directional backlight [9-11]. By delivering the directional light rays to each eye alternatively and synchronizing it with the alternation of right-eye and left-eye images on the LCD panel, a full resolution stereoscopic image can be attained. One of the common ways to attain a directional backlight is to use a convex lens combined with an active light source. A display system composed of a large aperture convex lens and a dot-matrix light source can attain autostereoscopy with plural viewpoints [12]. However, the required optical distance is deep and the system becomes bulky. To reduce the thickness of display hardware, use of a convex lens array has been proposed [13-16]. However, the image quality is poor because of the distinct seam in the lens array. Ishizuka et al. have realized homogenous brightness of image by using a vertical diffuser in front of the lens array [17, 18]. The uniformity of backlight is further increased by lens alignment with various phase shifts in each raw [19, 20]. The crosstalk level of this system, however, is high due to the field curvature of lenses. Pursuing a lower crosstalk level, Mukai et al. have proposed a method to place a large aperture lens to reduce aberration [21]. However, two layers of Fresnel lenses used in this display system not only requires heavy optical calculation, but also produces stray light causing crosstalk. As a solution to this problem, a directional backlight system using a single layer of decentered lens array has been proposed, but the crosstalk level is not low enough [22]. In this paper, we propose an autostereoscopic display system using a curved lens array to reduce the crosstalk level. Additionally, improvement of image quality and a lower crosstalk level are achieved by a lens array composed of trapezoid elemental lenses.