Superzone Fresnel Liquid Crystal Lens for Temporal Scanning Auto-Stereoscopic Display

Superzone Fresnel Liquid Crystal Lens for Temporal

Scanning Auto-Stereoscopic Display

Yi-Pai Huang, Chih-Wei Chen, and Yi-Ching Huang

Abstract—The fast response superzone Fresnel liquid crystal

(LC) lens with multiple transparent electrodes was proposed for

temporal scanning auto-stereoscopic display. The experimental

results indicated that the superzone Fresnel LC lens not only

performed fast switching time ( 0.2 s), but also had the benefit

of low driving voltage ( 5

). A 4-inch 2D/3D switchable

auto-stereoscopic display with superzone Fresnel LC lens was

further demonstrated. Finally, by driving the multiple electrodes

alternatively, the superzone Fresnel LC lens array could be

moved on horizontal direction for increasing the resolution of

auto-stereoscopic display.

Index Terms—Liquid crystal (LC) lens, Fresnel lens,

auto-stereo-scopic, 3D display.

I. I

R

ECENTLY, developing high quality glasses-free 3D

dis-play to produce more natural images has become a

cut-ting-edge technology. There are existing works such as

holo-graphic type [1], [2] and volumetric type [3]–[5] that have been

proposed for years; nevertheless, these large volume and

com-plicated systems are still an issue. Thus, another approach is the

multiplexed-2D method [6]–[11], which is widely used now due

to its easy implementation and high potential for flat panel

dis-play application. Furthermore, the electrically controlled liquid

crystal lens (LC lens) [12]–[16], which can be switched on and

off by changing the driving voltage, has also been proposed for

3D display application. Combining the panel with LC lens, the

2D/3D switchable display [17]–[23] is achieved and used to

dis-play high resolution images in 2D mode, and low resolution but

auto-stereoscopic images in 3D mode.

Although the LC lens can supply 2D/3D switching property,

the image resolution is dramatically decreased when switched

to multi-view 3D mode. Thus, Huang et al. [24] proposed

temporal scanning LC-lens to combine spatial-multiplexed

and time-multiplexed method for improving the 3D image

resolution, as shown in Fig. 1. However, the prior scanning LC

lens had thick LC-cell gap ( 60

m) which resulted in slow

Manuscript received May 17, 2012; revised June 14, 2012; accepted June 15, 2012. Date of publication October 02, 2012; date of current version November 19, 2012. This work is supported in part by National Science Council, Taiwan, under Academic Project NSC101-2221-E-009-120-MY3.

Y.-P. Huang and C.-W. Chen are with the Department of Photonics & In-stitute of Electro-Optical Engineering/Display InIn-stitute, National Chiao Tung University, 30010 Hsinchu, Taiwan (e-mail: [email protected]; [email protected]).

Y.-C. Huang is with the Taiwan Semiconductor Manufacturing Company, Science-Based Industrial Park, Hsin-Chu, Taiwan 300 (e-mail: yhuangs@tsmc. com).

Color versions of one or more of the figures are available online at http:// ieeexplore.ieee.org.

Digital Object Identifier 10.1109/JDT.2012.2212695

Fig. 1. Scheme of scanning time-multiplexed 3D display.

response and high driving voltage. According to LC response

time formula, shown in (1) [25], the response time can be

accelerated by reducing the cell gap

(1)

where

and

are viscosity, elastic constant, cell

gap, driving voltage, and threshold voltage, respectively.

Hence, Fresnel LC lens will be a good candidate for a

tem-poral scanning device. However, not every kind of Fresnel LC

lens can be used for temporal scanning function. Accordingly,

in this paper, we propose superzone Fresnel LC lens with

multi-electrode driven structure for fast switching, low-voltage

oper-ation, and temporal scanning.

II. S

F

LC L

T

S

The Fresnel LC lens can be grouped into three types: Fresnel

zone plate, continuous Fresnel zone lens, and superzone Fresnel

lens [26], [27], as shown in Fig. 2. Many prior approaches have

illustrated the switchable LC Fresnel zone plate uses the

polymer-stabilized method to form the fixed binary-zone

[28]–[31]. However, it is not suitable for scanning because the

phase of each zone is fixed by a polymer wall (Fig. 2). Lu et al.

[23] proposed continuous Fresnel LC lens formed by various

widths of Fresnel zone prisms (Fig. 2). Nevertheless, it is also

not available for scanning movement due to the width of each

Fresnel zone not the same as shown in Fig. 3(a). Therefore,

Fig. 2. Different structures of Fresnel LC lens—Fresnel zone plate, continuous Fresnel zone lens, and superzone Fresnel lens.

Fig. 3. Sketches illustrate that (a) the continuous Fresnel LC lens cannot be shifted for the same period; on the contrary; and (b) the scanning superzone Fresnel LC lens performs scanning function under shifting driving voltages. (Here, the lens shift from left side to right side, and the different gray levels on electrodes indicate different driving voltages.)

in this paper, we propose a superzone Fresnel LC lens with

equalized ITO pitch (Fig. 2). Consequently, the superzone

Fresnel LC lens can be shifted step by step by simply applying

the different voltages on each electrode sequentially, as shown

in Fig. 3(b). In the following section, the detail design and

optimization of superzone Fresnel LC lens will be illustrated.

III. S

O

In this paper, the parameters of a superzone Fresnel LC lens

are based on a 4-inch panel with pixel size 96

m, and the

viewing distance and view-number are of 96 cm and six-views

respectively. The superzone Fresnel LC lens array is slanted

9.46 relative to vertical direction of pixel to suppress the moiré

effect. Then, the corresponded six views image information is

addressed according to the slanted lenses. Hence, the six views

auto-stereoscopic display can be obtained [6]. Accordingly, the

total pitch of a single superzone Fresnel LC lens is 188 , and

it is divided into 6 zone prisms with equalized width. As

illus-trated in Fig. 4, different electrode patterns and ITO slit ratio

were simulated. In the reconstructed figures, blue dash-line

in-dicates the ideal curve of Fresnel lens, and the red solid-line

shows the simulated results. Consequently, multiple ITO

elec-trodes at both substrates with electrode to slit ratio equal to 2:1

is the optimized one, as shown in Fig. 4(b). The final parameters

TABLE I

PARAMETERS OF THEOPTIMIZEDSUPERZONEFRESNELLC LENS

for fabrication are listed in Table I. Each superzone Fresnel LC

lens has 24 fine electrodes at both substrates inside the LC cell.

And the cell gap of superzone Fresnel LC lens is almost half of

the prior scanning LC-lens [24]. Thus, the response time of the

superzone Fresnel LC lens are expected to be reduced to at least

a quarter of the prior approach. Finally, the focal length of the

LC lens also can be calculated from the following formula [21]:

(2)

IV. E

In this experimental session, the response time of proposed

superzone Fresnel LC lens is first illustrated. Following the

lens quality and proto-type of the auto-stereoscopic display are

demonstrated. Finally, the superzone Fresnel LC lens array is

driven to further perform scanning function on the horizontal

movement for increasing 3D image resolution.

In the measurement, a 632.8 nm He-Ne laser and a fast CCD

located at the focal plane were used to measure the intensity

distribution and response time. The overdrive method was also

used to further accelerate the response time. A pulse voltage

(3 times the stable driving voltage with 100 ms pulse width) was

firstly applied to electrodes to induce strong electric field in the

LC cell, and then switch to the stable driving voltage (5

,

1 kHz) to perform the final lens curvature. Fig. 5 shows the

mea-sured results. For the prior scanning LC-lens, its response time

was more than 6 s (green line), which was not enough for

tem-poral scanning. For the proposed superzone Fresnel LC lens,

its response time could be extremely reduced to 0.2 s with

ap-plying overdriving method [32], [33] (purple line). The captured

images for the superzone LC lens switching from off state to on

state are also shown in Fig. 6. Moreover, in order to reduce the

lens’ total switching time

, Chen et al. [34] also

proposed a dual-directional overdriving method which can

pro-vide vertical and lateral electric field to accelerate both LC lens’

rising and decay time.

For evaluating the lens profile, Fluorescence Confocal

Po-larizing Microscope (FCPM) [35], as shown in Fig. 7(a), was

utilized. The FCPM can measure the LC orientation of each

horizontal layer ( – plane) according to the captured

inten-sity. Fig. 7(b) shows a sampled intensity image of a single layer

within the LC cell. In the measurement, LC cell was divided

into 10 layers along the cell gap, -direction, as illustrated in

Fig. 7(c). The 1st and 10th layers were located at the boundaries

of top and bottom substrate respectively. Finally, the profile of

superzone Fresnel LC lens was reconstructed by integrating the

Fig. 4. Simulated cases for finding out the optimized structure design—Multiple electrode on both top and bottom side of substrate.

Fig. 5. Response time curves of prior scanning LC lens, and superzone Fresnel LC lens with/without overdrive method.

Fig. 6. Focusing images of the superzone Fresnel LC lens with overdrive method. The proposed superzone Fresnel LC lens becomes stable after 0.2 sec.

10 layers (Fig. 8). The result shows that the superzone Fresnel

LC lens was really established, yet the phase change was not as

ideal as simulated. By further analyzing the detail, it was caused

by the cell gap variation, which is smaller in fabricated sample

than that of ideal simulating condition.

After demonstrating a single superzone Fresnel LC lens, the

lens array for 4-inch 3D display was further fabricated. The light

intensity distributions of each viewing zone are shown in Fig. 9.

The distance between each view is 65 mm which is the average

gap of human eyes. The crosstalk of using superzone Fresnel LC

lens for 3D display here is around 25% according to (3), where

is the maximum intensity value for a single viewing zone at

a specific position, and

is the intensity value of the nearest

neighboring zone at the same position. Additionally, the

proto-type 4-inch 3D display with superzone Fresnel LC-lens is shown

in Fig. 10, which demonstrated the switched 2D and 3D images

respectively. And the captured images under 3D mode are also

clearly illustrated the different perspectives of the objects (e.g.,

the chairs)

%

(3)

In addition, we also briefly analyze the diffraction effect of

using our superzone Fresnel LC lens: for the lens-off state (2D

mode), because the Fresnel LC lens is aligned as homogeneous

cell (very small phase difference), as well as the ITO pattern is

thin (

nm thickness) and high transparent, the diffraction

Fig. 7. (a) Confocal microscope system. (b) A sampling intensity image captured by the confocal microscopy of a single layer inside the superzone Fresnel LC lens. (c) Different images captured along the cell gap,z-direction. (LC cell was separated into 10 layers for measuring in this paper.)

Fig. 8. Reconstruction of superzone Fresnel LC lens from experiment and simulation.

effect is not obvious (2D mode in Fig. 10); for the lens-on state

(3D mode), however, we can find slight color dispersion which

may caused by the discrete Fresnel prisms. Thus, suppressing

the color dispersion can be the next research topic.

Developing the fast response superzone Fresnel LC lens was

not only for switching between 2D/3D images, but also for

tem-poral scanning to produce high 3D image resolution. In our

ex-periment, 3 frames scanned (0.2

3

0.6 s) across a period of

LC lens, which means the 3D image resolution can be ideally

increased by a factor of 3. Fig. 11 shows the scanning results,

Fig. 9. Light distributions for 6-views 3D display using superzone Fresnel LC lens. The distance between each view is 65 mm at the viewing plane, and the horizontal-axis represents left-right direction of viewer.

Fig. 10. Snapshots under 2D and 3D modes from the proposed 2D/3D switch-able display using superzone Fresnel LC lens array. The captured images in 3D mode from two different viewing positions (view1 & view2) illustrate different perspectives.

where the scanning time was illustrated from top to bottom, and

the focus of the lens moved from left to right. The result

demon-strates that the proposed superzone Fresnel LC lens successfully

performs scanning function; however, the response time, which

is only 200 ms, still has to be improved for future temporal

scan-ning 3D display. Using the fast response LC material can be the

next step.

The blue phase LC (BP-LC) [36]–[38], ferroelectric LC

(FLC) [39], [40], and high birefringence LC (HB-LC) [41],

[42], are the three candidates. The BP-LC and FLC had

been demonstrated with sub-millisecond response speed. For

HB-LC, the cell gap of LC lens can be further reduced.

Con-sequently, by using the fast response LC material with the

proposed superzone Fresnel LC lens structure, a temporal

scan-ning 3D display for high resolution auto-stereoscopic image

can be achieved in the future.

Fig. 11. Captured images of scanning superzone Fresnel LC lens across a pe-riod of a LC lens (0.2 s/frame).

V. C

The 3D image resolution of current multi-view 3D display is

a major issue which needs to be improved. In prior approaches,

scanning LC lens for increasing the image resolution in

tem-poral domain was proposed, yet it still suffered from the slow

response time. In this paper, we proposed superzone Fresnel LC

lens to reduce the lens’s response time (from 6 sec to 0.2 sec),

as well as the driving voltage (from 30

to 5

). Not only

was a single lens, but also lens array was fabricated for a 4-inch

auto-stereoscopic display, which could perform fast switching

between 2D and 3D images. Moreover, the superzone Fresnel

LC lens with the equalized ITO pitch could be shifted step by

step by simply applying the different voltages on each

elec-trode sequentially. Finally, the scanning function was

success-fully demonstrated in the experimental result. In the future, a

full resolution temporal scanning 3D display could be achieved

by further implementing fast response or high birefringence LC

materials.

A

The authors also would like to thank A. Markman,

Univer-sity of Connecticutt, Storrs, B. W. Xiao, Y. H. Pai, C. H. Tsai,

Mrs. S. Y. Fu, K. J. Hu and J. F. Huang, ITRI, Taiwan, for their

valuable discussion and technical support.

R

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Yi-Pai Huang received the B.S. degree from

Na-tional Cheng Kung University, Hsinchu, Taiwan, in 1999 and the Ph.D. degree in electro-optical engi-neering from the National Chiao Tung University, Hsinchu, Taiwan, in 2004.

He is currently an full-time associate professor in the Department of Photonics & Display Institute, Na-tional Chiao Tung University, Hsinchu, Taiwan. Also he is a visiting associate professor of Cornell Uni-versity, Ithaca, NY, from 2011 to 2012. His expertise includes 3D display and interactive technologies,

dis-play optics and color science, micro-optics. In the above-mentioned research, he have so far published more than 110 International Journal and conference pa-pers (including the 57 SID Conference Papa-pers and 10 invited talks), and have obtained 25 granted patents, with another 48 patents currently publicly avail-able.

Dr. Huang is the secretary general of SID Taipei Chapter, and Chair of Ap-plied-Vision program sub-committee of SID. In addition, he had three times received the SID’s distinguished paper award (2001, 2004, 2009). Other impor-tant awards include 2011 Taiwan National Award of Academia Inventor, 2010 Advantech Young Professor Award, 2009 Journal—SID: Best paper of the Year Award, and 2005 Golden Dissertation Award of Acer Foundation.

Chih-Wei Chen received the B.S. degree from

Department of Mechatronics Engineering, National Changhua University of Education, Changhua, Taiwan, in 2007, and is currently working toward the Ph.D. degree from the Department of Photonics, Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu, Taiwan.

His current research is including high image-quality LCDs, 3-D displays, and liquid crystal lens design.

Yi-Ching Huang received the B.S. degree from

Department of Opto Electronic Communication Engineering, National Kaohsiung Normal Univer-sity, in 2007, and M.S. degree at the Department of Photonics, Institute of Electro-Optical Engineering, National Chiao Tung University in 2010.

She is currently a Process Integration Engineering at Taiwan Semiconductor Manufacturing Company, Hsin-chu, Taiwan.