Investigation of Autostereoscopic Displays Based on Various Display Technologies

Abstract

The autostereoscopic display is a promising way towards three-dimensional-display technology since it allows humans to perceive stereoscopic images with naked eyes. However, it faces great challenges from low resolution, narrow viewing angle, ghost images, eye strain, and fatigue. Nowadays, the prevalent liquid crystal display (LCD), the organic light-emitting diode (OLED), and the emerging micro light-emitting diode (Micro-LED) offer more powerful tools to tackle these challenges. First, we comprehensively review various implementations of autostereoscopic displays. Second, based on LCD, OLED, and Micro-LED, their pros and cons for the implementation of autostereoscopic displays are compared. Lastly, several novel implementations of autostereoscopic displays with Micro-LED are proposed: a Micro-LED light-stripe backlight with an LCD, a high-resolution Micro-LED display with a micro-lens array or a high-speed scanning barrier/deflector, and a transparent floating display. This work could be a guidance for Micro-LED applications on autostereoscopic displays.

Keywords: Micro-LED; autostereoscopic display; light-emitting diode.

Figure 1

(a) A 4D light-field function L(x, y, $\theta$, $\varphi$) fully presents the information of a 3D scene with a horizontal and vertical parallax. (b) To reduce the huge amount of information of a 4D light field, the $\varphi$-direction information is dropped and simplified into a 3D function L(x, y, $\theta$), and only the binocular and horizontal parallax is preserved.

Figure 2

The parallax barrier is located (a) in front of the LCD panel or (b) behind the LCD panel. The parallax barrier generates the binocular parallax.

Figure 3

In the four-view design, the pitch of the parallax barrier is slightly smaller than four times the subpixel pitch.

Figure 4

The lenticular-lens method used to produce a 3D image (top view) is plotted. It is similar to the parallax barrier; however, a lenticular sheet guides left-eye pixels to the left eye, and right-eye pixels to the right eye without blocking light.

Figure 5

The parallax barrier slits are shifted by one half pitch within 1/120 s, so both eyes can perceive red and blue pixels, and then the resolution is retained. (a) As t = 0 s, the parallax barrier is at the original place. (b) As t = 1/120 s, the parallax barrier shifts one half pitch.

Figure 6

(a) The first light bar is turned on and projects the first image to the first eye via the guide of the optical film. (b) Similarly, the second light bar projects the second image to the second eye. The two light bars are turned on and off alternatively. (Reproduced with permission from ref. [42]).

Figure 7

ITRI proposed a scanning LC-prism array to bend the light to different directions sequentially and realized a time-multiplex display [45].

Figure 8

(a) Without applying an electric field, the LC lies down and behaves as $n_e$, and the ray is bent to left owing to $n_e>n$. (b) By applying an electric field, the LC stands up and behaves as $n_o$ that bends the ray to the right due to $n_o<n$ [45].

Figure 9

The principle behind integral imaging: The light field is reconstructed by the rays from the 2D display, which are directed to the voxel’s position by the micro-lens 2D array and intersect with a voxel.

Figure 10

(a) The wavefront of the object beam interferes with the reference beam, and the fringe is recorded on a photo film to form a hologram. (b) Illuminating a hologram with the original reference beam reconstructs the wavefront of the object beam, so it includes the phase and amplitude such that eyes sense the depth of the object.

Figure 11

(a) The viewing zone pitch is small in a thick-encapsulation-layer system, such as LCD, that has a thick front glass around 0.5 mm. (b) The thin-encapsulation-layer system, e.g., OLED/Micro-LED has an ultra-thin film less than 1 µm, which shows a large viewing zone pitch.

Figure 12

The pentile-pixel-arrangement image captured from an OLED display, showing a more sophisticated pattern than the RGB pattern of LCD, such that it is trickier to design the parallax barrier or lenticular pattern.

Figure 13

We have implemented an autostereoscopic display with an OLED smartphone. Comparing the (a) left, (b) middle, and (c) right views, the relative positions of petals and trunk (in the red circle) are different, and it shows a horizontal parallax.

Figure 14

The Micro-LEDs form a light-stripe 1D array with a well-designed pitch, such that the partial pixels are projected to the corresponding views.

Figure 15

Introducing multiple sets of light-stripe arrays (grouped by colors) and switching each set of light stripes on and off sequentially allows every pixel to be perceived at each view. It is a time-multiplex method to achieve full resolution. Here, only the rays emitted from a single light-stripe set are plotted, and each view receives four pixels rather than a single pixel to demonstrate that a full-resolution image is perceived.