Organization of this Thesis

The thesis is organized as following: The principles of the proposed 3D double-screen display are presented in Chapter 2. In Chapter 3, design of lenticular-lens-based micro-optical structure for 3D and double-screen functions were invented and simulated. Moreover, manufacturing the lenticular-lens-based micro-optical structure by excimer laser micromaching system will be explored in Chapter 4. In Chapter 5, the mechanism of applying the optical system in the

Chapter 2

Principles of Proposed 3D Double-screen Display

2.1 Overview

“Can you image one is watching a baseball game and searching the baseball players’ data on the internet at the same time?” The answer to this survey will most likely be positive. If there is an additional assumption that both images are viewed in full-screen size and generated from a single panel display, will you still believe the possibility of this statement? I believe the responds will now become disappointed.

However, as a novel 3D double-screen display is proposed, the situation of watching full-screen-sized diverse channels from a single panel is no longer impossible.

In order to design a double-screen display with realistic feeling on images, the study will begin with knowing the fundamental principles of 3D vision. After that, various technologies of generating dual-view and 3D images, such as the methods of stereoscopic and auto-stereoscopic types’ displays, will be discussed and compared.

The analyzed results will show a better candidate to utilize for further research. Hence, the 3D and double-screen functions will be developed and introduced. The full design concepts of the proposed novel 3D double-screen display system will also be presented.

2.2 Principles of 3D Vision

Three-dimensional information is formed by complex activities in the brain and obtained by the visual system. A lot of related researches have been made in this field [2]. There are several clues to depth perception by the visual sense as shown in Fig.

2-1 [3, 4].

Convergence

Convergence is effective when the distance between eyes and objects is within 20 m. Convergence rapidly loses its influence on the visual system as the distance increases because the convergence angle becomes smaller.

Binocular Parallax

Binocular parallax occurs when there are other objects in front of or in the rear of the object on which the right-left eyes are focused. If the degree of this binocular parallax is sufficiently small, the images are combined and the observer has a clear sensation of depth in front and behind the object. The binocular parallax is valid and precise in distinguishing the depth difference, i.e. the difference in the distance between several objects. It plays the important role in understanding the relative position of objects within 10 m.

Accommodation and Motion Parallax

Accommodation is only effective when the observation distance is no more than

Others

Visual information received by one eye is not the same as that through the other eye, but we perceive these data as a single image. Namely, binocular vision which appears to be based on interaction of the right and left images is an important function in the design of a 3D display. Besides, the distance between the pupils of the human eyes is approximately 65 mm which is adopted when considering the viewing conditions.

Fig. 2-1. Depth clues and display factors.

2.3 3D Display Technologies

The first of 3D display went back to the early 1800s. However, most applied 3D technologies were proposed after the middle of 20^th century. In these few years, the 3D displays have their widespread applications. Generally speaking, the 3D displays can be divided into stereoscopic displays and auto-stereoscopic displays.

2.3.1 Stereoscopic Displays

Stereoscopic displays are needed to wear a device, such as polarized glasses, which ensures the left and right eye’s views are received by the correct eye. Many stereoscopic displays have been proposed [5, 6]. Most of them have widely used in many fields but suffer from the drawbacks that the viewer have to wear, or be very close to, some devices to separate the left and right eye’s views. Those requirements limit the widespread attraction of stereoscopic displays as personal displays.

2.3.2 Auto-stereoscopic Displays

Auto-stereoscopic displays do not require the user to wear any device to separate the left and right views and instead send them directly to the correct eye. This removes a crucial obstacle to the appealing of 3D display.

Various auto-stereoscopic technologies have been proposed. The principles of several technologies [7] are discussed in the following.

Volumetric type

scattering medium with a scattering laser beam [8], as shown in Fig. 2-2(a). Another is to project or scan layered images on a spatial designed screen to create a volumetric image profile [9, 10], as shown in Fig. 2-2(b). The other is to induce psychological effects with use of a super-large image projection screen [11], as shown in Fig. 2-2(c).

Holography

Holography is utilized the laser beam to form the illumination beam and reference beam. Thereafter, the interference fringes can be displayed by the superposition of rays from each object point [12], as shown in Fig. 2-2(d).

Integral imaging

Integral imaging [13, 14] is composed of a micro-lens array, the pickup device, and the display device. By means of micro-lens array, the pickup device can pick up several images with the different angles. By combining these pick up images, the 3D images can be revealed, as shown in Fig. 2-2(e).

Stereo pair

The stereo pair type is including spatial-multiplexed and time-multiplexed display.

Both of them require viewing zone forming optics to send the stereo pairs’ images to the correct eye. The viewing zone is a region where the viewers can see the whole images displayed on the screen. There are two viewing zones to match each eye, than forming a complete 3D vision. In order to form the 3D perception, each display system is needed a specific optical power. The spatial-multiplexed type displays show the stereo pairs’ images at the same time, and the time-multiplexed type displays have the stereo pairs’ images sequentially, as shown in Fig. 2-2(f).

For the spatial-multiplexed method, the well-known examples are the flat panel with a lenticular screen [15] or a parallax barrier [16, 17], as shown in Fig. 2-3. The concept of using the lenticular screen or the parallax barrier is to separate the images displayed on the panel to form the parallax images. After the parallax images received by human eyes, the brain will reconstruct them to form 3D images.

For the time-multiplexed method, its development was restricted in early periods because the fast response time display was not available. During these few years, there are some designs for time-multiplexed 3D display proposed, such as K. W. Chien’s, as shown in Fig. 2-4 [18], and Y. M. Chu’s, as shown in Fig. 2-5 [19]. The idea of the design is that the parallax images are formed by sequentially switching backlight with focusing foil or the dual directional backlight system. The lightguides provide with right or left eye’s light sources to each eye respectively. By switching the light sources sequentially, the stereo pairs’ images can be perceived by eyes one after another, then form the 3D image.

Method (a)

Method (b) Method (c)

Method (d)

Method (e)

Object Pickup

Pickup device Lens

array

Elemental image

Display device Reconstructed

image Display

Method (f)

Fig. 2-2. Examples of 3D methods: (a) volumetric 3D display system with rasterization hardware; (b) a solid-state multi-planar volumetric display; (c) DSHARP - a wide screen multi-projector display; (d) color images with the MIT holographic video display; (e) the concept of integral imaging; (f) the principles of stereo pair type: spatial-multiplexed and time-multiplexed displays.

a) b)

Fig. 2-3. The stereo type of 3D display (a) parallax barrier and (b) lenticular-lens.

Fig. 2-4. 3D mobile display based on sequentially switching backlight.

Fig. 2-5. 3D mobile display based on dual directional stacked lightguides.

2.3.3 Comparisons of 3D Methods

By summarizing various 3D display technologies introduced, there are two ways to generate the sense of depth. The first one is to simulate the objects in the real space, as mentioned by methods (a) to (d). The other is to directly send pairs of parallax images to each eye respectively, as mentioned by methods (e) and (f). These 3D displays can yield acceptable 3D images, but most of them can not provide the solutions to our design completely.

According to the 3D image qualities, system size and cost, each 3D method has their advantages and disadvantages as shown in Table 2-1[20]. The major drawback of stereoscopic display is needed to wear a device. Moreover, the volumetric display often has the drawbacks of bulky and 3D effect limitation. Furthermore, the holographic display has the poor feasibility due to the requirement of ultrahigh technical support. The concept of integral imaging is similar to the stereo pair but has the drawback of low image resolution. The overall evaluations of the stereo pair type are the most appealing, not only has compatibility with the current 2D display technology but also maintain the image qualities. Besides, the stereo pairs display has higher feasibility than the other 3D methods. Therefore, the stereo pair display is a better candidate to be widely applied for most of available auto-stereoscopic displays.

Table 2-1. Comparisons between various 3D displays.

Auto-stereoscopic

The stereo pair displays contain two methods, spatial-multiplexed and time-multiplexed. Both of them are commonly chosen. However, the time-multiplexed type displays have some issues on alignment and response time in

were too flat to guide light effectively. Then, Y. M. Chu provided the solution in her design [19], but moiré pattern is formed by the periods of color filter and two stacked lightguides. Even in Y. C. Yeh’s design [21], moiré pattern can not be eliminated completely. Therefore, due to the heavy uncertainties of time-multiplexed method, we choose to utilize the other more mature method, spatial-multiplexed.

2.4 Dual-view Display Technologies

In 2005, a new type of display which could perform dual full sized images simultaneously has been announced [27]. The users at right side of the panel could enjoy the TV game while the other observers at left side were watching the video content such as a movie or a TV broadcast. The differences of single-view and dual-view displays are shown in Fig. 2-6.

a) b)

c) d)

Fig. 2-6. Concept of a) single-view and b) dual-view display, and c) single-view and d) dual-view images.

These dual-view TVs were basically designed from extending the 3D display technologies. The stereo pair type spatial-multiplex systems including parallax barrier and lenticular-screen are the general methods as shown in Fig. 2-7. The first prototype dual-view display is using parallax barrier. Superimposing the parallax barrier as the external micro-optical layer on an ordinary TFT-LCD as their two-way viewing-angle LCD was proposed [27]. The observers standing at left or right positions can view the left or right side images, respectively. The opposite images are blocked by the parallax barrier. Because parallax barrier is designed to block certain areas of images, the light efficiency becomes half of the ordinary. Therefore, some research groups are investigating on utilizing the lenticular-screen [28]. The left and right side images are re-directed by the lenticular-screen to left side and right sides, respectively. This will enable the viewers standing at each side to receive different visual information.

a) b)

Fig. 2-7. The stereo type of dual-view display (a) parallax barrier and (b) lenticular-screen.

2.5 Design of Single Panel 3D Double-screen Display

Among various display technologies developed to visualize 3D and dual-view images, the lenticular-lens based spatial-multiplexed method has been selected in our research to enjoy its benefits of high brightness and availability of generating multiple views [21, 22]. In deed, the extension of concept on generating multiple views shows a set of the lenticular-lenses can split and guide the images to the specific directions and to perform either 3D or dual-view function by the proper lens design [23].

The difference between dual-view and double-screen functions is the amount of images perceived by viewers. By utilizing dual-view function in the display, observers standing at left and right of display can see different images as shown in Fig. 2-6 b).

However, double-screen function is designed with a planar mirror attached for observers to perceive two different images at the same time as shown in Fig. 2-8.

Since dual-view and double-screen functions are the medium in generating two images, the methods used in dual-view function can be implanted in double-screen function.

The proposed 3D double-screen display, as shown in Fig. 2-8, consists the top screen, a panel with micro-optical structure attached as shown in Fig. 2-9, and the bottom screen, a mirror. Each screen is designed to create the independent 3D images.

Thus, the micro-optical structure needs to have both 3D and double-screen functions, which means to have the ability to re-direct the incident light to the specific viewing regions. Therefore, the design concepts and working principles need to be further investigated.

Fig. 2-8. Concept of the proposed 3D double screens display system.

Fig. 2-9. Configuration of the top screen with micro-optical structure.

2.5.1 Model Adopted

After the evaluation of varies 3D method, spatial-multiplexed method including parallax barrier and lenticular-screen has been chosen to be the candidate in our

Bottom Screen:

Mirror Top Screen:

Panel with Micro-Optical Structure

Notwithstanding parallax barrier can block the undesired image sectors, the brightness and resolution of entire viewing images will be reduced. Besides, although lenticular-lens has similar result on reducing the resolution, the generated split images have smaller crosstalk and higher brightness. Thus, lenticular-lens is a better option to enlarge the viewing angle in our design.

Table 2-2. Comparison of displays using lenticular-lens and parallax-barrier.

Parameters Parallax Barrier Lenticular Lens

Crosstalk 2% ~ 10% < 1%

Brightness < 50% > 100%

Resolution 50% 50%

2.5.2 Functioning Principles

As implied by the novel display’s name, “3D double-screen display” needs to have 3D and double-screen functions. In order to accomplish both functions, we can combine a layer performing 3D function and another layer with double-screen function.

In addition, the proposed system has top and bottom screens. According to Snell’s Law of refraction, the information which contains top and bottom screens images can be split by the functional layer to the respective screen in the top or bottom direction, respectively. In order to see images on both screens at the same time, the bottom screen is designed to be a mirror. According to the Law of Reflection, the mirror could be used to redirect the images to the observer. The observer can view top screen images directly from the panel and bottom screen images from the mirror simultaneously.

Besides, 3D image contains left and right eye’s images. The 3D functional layer has to direct the respective images to each eye in left and right directions. Hence, in combining both functions together, both layers of lenticular-lenses have to be located perpendicular to each other as shown in Fig. 2-10. 3D and double-screen functions will then be appeared simultaneously in horizontal and vertical directions, respectively. Consequently, the lenticular-lens-based micro-optical structure including two functional layers of lenticular-lenses dominates the light source of the display system will be the most important part of this study.

Fig. 2-10. Schematic of the micro-optical structure.

2.6 Applied Fields of 3D Double-screen Display

There are many fields can be applied the proposed 3D double-screen display on.

The most effective examples for getting the benefits from the design are listed in Table 2-3.

Bottom set of lenticular-lens:

Double-screen function layer Top set of lenticular-lens:

3D function layer

Ordinary panel

Table 2-3. Possible fields of using 3D double-screen display.

3D map of vehicle control Stereo video phone and mobile phone

2.7 Summary

After reviewing the 3D vision principles and display technologies, a new system model is proposed by utilizing lenticular-lens as medium of the micro-optical structure to perform dual-functioning on a single unit. By pasting the micro-optical structure onto a panel and adding on a mirror, the system can generate two diverse images without shrinking their scales in a single display. Users can watch the TV program on a panel and use another one to track the information on internet. This innovative feature is applicable to the products such as notebook PCs, mobile phones and hand-held devices etc. with convenience and cost advantage of showing two information channels simultaneously. The accuracy of presented images, which is heavily depended on the shape and size of lenticular-lens, is the objective of the research. Due to lens’ profile affected by the pixel size, the layout styles of color filter are examined. In order to yield better viewing performance, the optimized design and

Having a screen shows the picture images while another screen describes the reference data.

simulations of the micro-optical structure will be further studied and analyzed in Chapter 3.

Chapter 3

Design of Lenticular-lens-based Micro-optical Structure for 3D and Double-screen Functions

3.1 Introduction

The lenticular-lens based micro-optical structure can be used to re-directing the incident light from the panel and functioning 3D and double-screen images. However, the uncertainty of the lens design may narrow down the viewing angle and result the images in the unexpected viewing zones [24, 25]. The unexpected position of an image causes the interference with the other image, as called crosstalk [26]. Thus, the design on lens-based micro-optical structure is very important for generating the 3D and double-screen images.

3.2 Optical Design of Micro-optical Structure

The micro-optical structure contains two lenticular-lens layers for functioning 3D and double-screen images. In order to operate precisely and obtain the images correctly, pixel size, viewing distance and viewing angle have to be considered in designing the micro-optical structure. Thus, the novel system structure has proposed and the related equations have derived. Finally, the further adjustment on these parameters can result an optimized viewing performance.

3.2.1 Lens Design

One of the advantages using lenticular-lens is having the magnification ability.

Because the spatial-multiplexed method requires a single image to be split into left and right sides images, there will occur the black strips in that empty slots. However, the magnification ability of the lens will cover them to provide a continuing image in the spatial domain. The magnification m of the lenses is given by the ratio of the interocular distance e and the LCD pixel pitch i. Geometrically, this ratio is also the ratio between z and f.

(3-1)

As with parallax barrier displays, the effective of viewpoint to see the correct left and right images is determined by pixels at the edge of the display. The lenticular-lens based 3D displays, however, have a little difference on determining the effective viewing zone as illustrated in Fig. 3-1 [34]. The lenticular pitch needs to be set so that the centre of each pair of pixels is projected to the centre of the viewing windows [34].

The specific parameters of the lenticular-lenses are the lens pitch l and the viewing distance z. The relationship between pixel pitch i and lenticular-lens pitch l can be found by considering similar triangles.

(3-2)

After sorting the equation,

Typically the pixel pitch is set by the choice of ordinary display and the minimum focal length, f, determined in large part by the substrate thickness on the front of the display.

The distance, z, between the color filter and the observer has the relationship by considering the other similar triangles,

(3-4)

By reorganizing the equations,

By reorganizing the equations,