Landscape/Portrait Dual Mode Lens Type 3D Display Using a 2D Lens Array

Ching-Tsun Chang, Wen-Lung Chen, Chih-Hung Shih, Wei-Ming Huang * AU Optronics Corporation, No. 1, Li-Hsin Rd. 2, Hsinchu Science Park, Hsinchu 30078, Taiwan, R.O.C.

Abstract Traditionally, a lenticular lens array, which is a one-dimensionally

periodic lens structure, is used in front of a image display, such as

LCD or OLED, to achieve human 3D perception. Due to its one-

dimensionally periodic property, most of this kind of 3D displays

can show 3D in only one display orientation. In this paper, we

utilize a 2D lens array instead to achieve human 3D perception in

both landscape and portrait display orientation. The 2D lens

array is fabricated using ink-jet printing (IJP) technology and the

3D function is demonstrated successfully.

Author Keywords autostereoscopic; lenticular; barrier; ink-jet priting

1. Introduction 3D display technologies give people new and more impressive

viewing experiences and are under increasing development.

Among them, lenticular lens [1] and parallax barrier [2] are two

major technologies used to achieve autostereoscopic displays. No

matter which technology is used, they all provide 3D perception

through binocular disparity, by which left eye sees only left eye

image and right eye sees only right eye image through different

viewing angle. Under this condition, human brain fuses these two

images into 3D illusion. Figure.1 shows the binocular disparity

and the possible types of disparity that produce different 3D

depth.

(a)

(b)

Figure 1. Illustration of binocular disparity (a) and different

types of disparity (b).

The parallax barrier achieves 3D by blocking the right-eye signal

toward left eye and the left-eye signal toward right eye. It’s a

relatively simple way and the fabrication of parallax barrier is

compatible to LCD process. However, the parallax loses

brightness due to the blocking of light (Figure 2 (a)). The

lenticular lens doesn’t suffer the brightness loss as parallax

barrier. The lenticular lens refracts the left-eye signal to the left

eye and right-eye signal to the right eye (Figure 2 (b)).

(a)

(b)

Figure 2. The principle of parallax barrier (a) and lenticular

lens (b).

Both the stripe parallax barrier and lenticular lens can provide 3D

perception in one direction such as landscape viewing mode or

portrait viewing mode. Because the blocking effect of parallax

barrier and the lens convergence only happen in the direction

perpendicular to stripe parallax barrier or lenticular lens. For LC

barrier, landscape/portrait dual mode can be carried out by design

orthogonal ITO electrode on top and bottom plate in one cell.

However, lenticular lens can not do the same thing in one

lenticular lens sheet due to its physical structure.

To provide 3D effect in both landscape and portrait viewing

mode, the lens convergence effect in both mode is necessary. The

most straight-forward method is to use spherical lens with proper

aperture geometry instead of cylindrical lens. This paper uses

spherical lens 2D array with proper horizontal and vertical pitch.

It is called 2D lens array in this paper.

2. 2D Lens Array Design As mentioned in previous section, we use 2D lens array to achieve

landscape/portrait dual mode 3D viewing. In this section, we are

going to explain the basic design parameter of 2D lens array.

As shown in figure 3, the lens pitch should be properly design to

ensure that people can see correct signals through each lens

element at the desired viewing distance. Because average inter-

pupil distance is about 65mm, we design the lens pitch based on

this condition. Figure 3 take parallax barrier as an example,

however, the pitch design is the same for both parallax barrier and

lenticular lens. Without proper pitch design, observer cannot see

3D across whole display.

Figure 3. Proper pitch design make observer sees correct

signal through 3D optical device element.

With proper lens pitch design and a specific thickness between

lens and pixel plane, 3D optimal viewing distance is inversely

proportional to the size of horizontal minimum driving element

(not necessary equal to the minimum displaying element), which

is pixel size as RGB arranged vertically and one-third pixel size as

RGB arranged horizontally. Therefore, here comes the problem.

As shown in Figure 4 (a), if a 2D lens array element covers two

minimum driving elements in both landscape and portrait viewing

mode, the optimal viewing distance of one viewing mode is three

times the other. In order to match optimal viewing distance of

both viewing mode, the lens pitch of the viewing mode with

longer optimal viewing distance should be re-designed based on

one-third average inter-pupil distance. However, this causes

different horizontal viewing freedom in both viewing mode.

Therefore, we design that the 2D lens array has the horizontal lens

pitch equal to the vertical lens pitch to achieve optimal viewing

distance matching with nearly equal horizontal viewing freedom

in both viewing mode (Figure 4 (b)).

(a) (b)

Figure 4. Illustration of optimal viewing distance matching.

With lens pitch design fixed, we now move to lens power design.

As known, lens power is a main factor determining the final 3D

performance. With focus design (lens focus closed to the pixel

plane), 3D minimum crosstalk would be low and horizontal

viewing freedom high, but moiré contrast would be higher. With

de-focus design (lens focus away from pixel plane), the

performance goes to the inverse trend. Hence, we should try to

strike a balance between these indices by modulating the lens

power.

The model we select is 3.97” with resolution 854 × 480. And we

choose four different radius of curvature, 250µm, 390µm, 500µm,

650µm to compare the minimum crosstalk, horizontal viewing

freedom and moiré contrast.

3. 2D Lens Array Fabrication In this paper, we select ink-jet printing as the technology

fabricating the 2D lens array. This technology let us easily prepare

2D lens array with accurate pitch and desired radius of curvature.

The first step of the process flow is to fabricate hydrophobic

transparent wall patterns by photolithography and these patterns

define the shape of the lens aperture. The second step is to drop

proper amount of lens material (the UV-curable high solid ink

containing <PDVTM> for the high reflective index) in the region

confined by the hydrophobic patterns and the lens material forms

a spherical surface itself due to surface tension. The third step is

to crosslink the lens material by UV exposure. All the materials

used are provided by Nippon Steel Chemical Co., Ltd and the lens

material is printed by Ulvac. Inc.

As shown in Figure 5, the line width of the hydrophobic patterns

is about 16um. The final lens samples have a blank region

uncovered by lens because the hydrophobic property and the

amount of lens material dropped.

(a) (b)

Figure 5. The OM image of hydrophobic patterns (top) and

2D lens array (bottom). Both 2D lens array with rectangle and

square aperture are shown.

4. Experiment Result 2D lens array successfully provides 3D effect in both landscape

and portrait viewing mode. Figure 6 shows the optical

performance measurement results of 250µm radius of curvature

and square aperture. The brightness oscillation frequency in

portrait viewing mode is three times in landscape viewing mode

because the spatial frequency of transmittance of pixels in portrait

viewing mode is three times in landscape viewing mode. This is a

direct evidence that 2D lens array provides lens effect and 3D

effect in both landscape and portrait viewing mode.

The brightness non-uniformity in landscape viewing mode is

severe than portrait viewing mode. That is also due to different

pixel transmittance spatial frequency in two viewing modes. With

a specific physical lens structure, the lens spot size is ideally

identical in both viewing modes. The brightness is more uniform

if the spot size is more closed to the pixel transmittance spatial

frequency in that viewing mode. Hence, the spot size is more

closed to the pixel transmittance spatial frequency in portrait

viewing mode which is three times in landscape viewing mode.

The minimum crosstalk is about 10% in both viewing mode,

which is higher than that of lenticular lens. Because the brightness

non-uniformity and the crosstalk distribution profile, the blank

region might be one of the main source contributing to crosstalk.

Figure 6. Optical performance measurement results of 250µm

radius of curvature and square aperture.

Figure 7 shows the OM images of 2D lens array of different radii

of curvature. The width of blank region gets wider with the radius

of curvature. That is because less lens material is used to achieve

lower lens sag. From the figure, blank region width is about 8µm

for 250µm radius of curvature, 12µm for 390µm and 500µm, and

much larger than 16µm for 650µm.

(a) (b)

(c) (d)

Figure 7. OM images of 2D lens array of 650µm (a), 500µm

(b), 390µm (c), 250µm (d).

As observer sees through a lenticular lens or a 2D lens array at a

specific viewing angle, lenses converge the light through lens

aperture into a small spot and project onto a specific position of

pixel plane. Blank region is uncovered by lens elements and

provides no convergence function. Hence, the blank region is

projected onto incorrect position and causes high crosstalk. The

wider the blank region is, the higher the minimum crosstalk.

Figure 8 shows the optical performance measurement results of

different radius curvature. From the figure, the minimum crosstalk

increases with the width of blank region. Moreover, the lens effect

in two orthogonal directions is hardly controlled identical if blank

region is closed to or larger than the size of hydrophobic patterns.

Hence, the crosstalk performance is unbalanced between

landscape and portrait viewing mode for 2D lens array with larger

blank region.

(a)

(b)

(c)

Figure 8. Optical performance measurement results of 390µm

(a), 500µm (b) and 650µm radius of curvature and square

aperture.

Since the intensity distribution is the result of convolution of the

lens transmittance distribution projected onto pixel plane and the

pixel transmittance distribution, we try to simulate the effect of

the blank region. Figure 9 shows the simulated spot distribution

with and without blank region for 250µm radius of curvature. For

lens without blank region all energy passing lens aperture is

converged to a spot. For lens with blank region the energy passing

through lens-covered region is converged to a spot and lens-

uncovered region is directly projected onto pixel plane. Hence, the

blank region contributes to a background crosstalk even if the spot

is projected within the pixels displaying correct signals.

Figure 10 shows the simulation results. From the top figure, 8μm

blank region contributes to about 4% minimum crosstalk at one

arbitrary viewing position. (The horizontal axis represents the spot

position on pixel plane not the viewing angle.) Due to lens effect

in two orthogonal directions and two-dimensional pixel

transmittance distribution, the horizontal crosstalk distribution

should depend on the vertical position of observers. The bottom

figure shows the effect of observer position and the theoretically

highest minimum crosstalk is about 8% which is closed to the

experiment results.

Figure 9. The simulated spot distribution with and without

blank region for 250µm radius of curvature.

(a)

(b)

Figure 10. The simulation result of effect of blank region.

Figure 11. 3.9” lens type 3D display using a 2D lens array.

5. Summary In this paper, we demonstrate the landscape/portrait dual mode 3D

display using 2D lens array and explain the design concept. We

also explain the source of minimum crosstalk. Therefore, it’s

possible to achieve much better performance with narrower blank

region.

On watching this prototype, 3D function works well in both

viewing mode. This kind of 3D display can also display 2D image

by suitable content arrangement. As this technology is applied in

the image display with higher PPI, such as retina display, it can

provide 3D as well as 2D with good image quality.

6. Acknowledgements This paper is partially supported by Nippon Steel Chemical Co. ,

Ltd. and Ulvac. Inc.. The substrate with the transparent wall and

the UV curable ink for the lens was kindly provided by Nippon

Steel Chemical Co., Ltd.. The 3D lens was kindly formed by

Ulvac. Inc..

7. References [1] G. J. Woodgate, J. Harrold, “High Efficiency Reconfigurable

2D/3D Autostereoscopic Display”, SID 03 DIGEST pp394-

397.

[2] H.J. Lee, “A High Resolution Autostereoscopic Display

Using a Time Division Parallax Barrier”, SID 06 DIGEST

pp81-84.

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0 50 100 150 200 Vertical Shift 0Vertical Shift 5Vertical Shift 10Vertical Shift 15Vertical Shift 20020406080100

0 50 100 150 200Crosstalk L with Blank Crosstalk R with Blank Crosstalk without Blank