Numerical Aperture vs. Operation Voltage

To judge the operation voltage, we take the numerical aperture (NA) into account as shown in Eq.5-3, where n is the index of refraction of the medium in which the lens is working and D is the diameter of the lens. Here our aperture is 1508um. With same numerical aperture a lower operation voltage was obtained by using MeDLC Lens because it can control the liquid crystal profile by each segment electrode. The numerical aperture with same operation voltage of multi-electrode and double electrode lens were compare as well. From the result the multi-electrode is higher than the double electrode and that means it has higher optical power to banded or focus the light of 3D display. And the numerical aperture is about a factor of 1.66 higher than the double electrode as shown in Fig. 5-9. Therefore, a better optical power as a cylindrical lens and lower operation voltage was indicated. The crosstalk phenomenon can be described by numerical aperture as well. A small numerical aperture can also mean a large focal length; in this case the effect of crosstalk can be serious due to a close image of left and right as shown in Fig. 5-10 (a). As for the large numerical aperture which result in a small focal length can separate the image of both eyes widely, therefore can have a lower crosstalk phenomenon.

f

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Fig. 5-9 Numerical Aperture property

High Crosstalk Low Crosstalk

f Left

eye Right

eye

Left eye Right

eye

f r (mm)

Normalizedintensity

0 1

r (mm)

Normalizedintensity

0 1

(a) (b)

Fig. 5-10 The crosstalk of (a) small numerical aperture (b) large numerical aperture.

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5.4 Summary

For the lens- like distribution, beam size, crosstalk, numerical aperture and operation voltage of conventional double electrode LC lens and proposed design MeDLC are summarized in Tab. 5-2. The beam size is reduced by 35% and the crosstalk with proposed MeDLC is lower about 43%. Furthermore the operation voltage of MeDLC Lens is lower than the double electrode lens and have a numerical aperture improves by 66%. In addition, the results indicate that the 2D/3D switching display with proposed method not only smaller beam size and lower crosstalk, but lower operation voltage.

Tab. 5-2 Comparison of conventional and proposed MeDLC.

Δ: High O: Low

Decrease Factor

x0.65 1

Crosstalk (%)

~24 ~42

Numerical Aperture

Increase Factor

x1.66 1

Operation voltage

O Δ

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Chapter 6

Conclusions and Future Work

6.1 Conclusions

In our opinion a viable 3D display should fulfill the following requirements:

1. The display should be auto-stereoscopic. It should allow freedom of movement with multi viewer potential.

2. The development of 3D display should motivated by trying to realize the image appears more natural.

3. The display should be able to display uncompromised 2D content.

Therefore, a novel active device of 2D/3D switching display has been demonstrated in this thesis. The principle of proposed method is to produce a natural 2D and 3D images by controlling the liquid crystal with switching ON and OFF the voltage. The simulation results indicate that a closer lens- like distribution can be achieved by our device. The measurement result also indicates that our device can be closer to the ideal lens- like distribution. And the numerical aperture (NA) of our device shows an improve by a factor of 1.66 which can result in a smaller volume of display and smaller crosstalk. Also the voltage requirement is much lower with same NA. In addition, due to a smaller beam size of proposed design the crosstalk of our device is lower than that of the conventional double electrode LC lens about 43%. In conclusion, the 3D displays with proposed method not only smaller beam size and lower crosstalk, but lower operation voltage.

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The proposed design can also be applied for combining with a head tracking device. By tracking the position of the head and a LC lens which is able to move horizontally with respect to the viewer position. Therefore, a freedom of movement with wide viewing angle and high resolution 3D images can be perceived.

6.2 Future work

Currently although our operation voltage is lower than that of the conventional double electrode LC lens (current operation voltage of MeDLC lens is about 30 volt).

Nevertheless we think this is not lower enough due to a thick glass substrate (550um) between the electrodes and liquid crystal. In order to further reduce the operation voltage the thickness of the substrate between the electrodes and liquid crystal lens must be reduced as shown in Fig. 6-1. And our task in the future is to study and find a suitable thickness and parameter (ε: dielectric property) of a dielectric layer. And with more electrodes to control the lens-like profile which will also be an optimized design.

Fig. 6-1 Reduce the operation the voltage by reduce the substrate thickness with an optimized parameter and structure design.

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Also from calculating the intensity distribution of MeDLC and without MeDLC when off state as shown in Fig. 6-2. The intensity distribution with MeDLC shows a diffraction pattern from ITO. This will reduce the image quality in displaying 2D images. To overcome this problem is to coating a material which has the same absorption and refraction rate corresponding to the ITO. In this case the phenomenon of diffraction can be reduce and without losing the quality in 2D mode. Therefore we will further study about this kind of material in the future.

CCD image

0 255

(a)

V=0V

Aperture size : 1.5mm

CCD image

0

V=0V 255

Aperture size : 1.5mm

(b)

Fig. 6-2 without driving voltage (a) MeDLC (b) without ITO pattern

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Beside the issue of operation voltage and diffraction in off state. In this research even though the crosstalk can reduced to 24% only. However, the effect of crosstalk in multi- view autosterescopic 3D displays has been reported that the tolerance limit of visual comfort is around 10% [34]. Therefore our second task is to red uce the crosstalk to about 10%. At previous chapter we have described the relative between the focal length and crosstalk. Fig. 6-3 shows a simulation of the trend of the crosstalk versus focal length. From the result, in order to achieve a 10% crosstalk our focal length needs to be reduced to about 1.9cm. And this can be resolved by larger the cell gap or change a liquid crystal which has high Δn.

Fig. 6-3 Crosstalk vs. focal length

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