A temporal backlight with multi-view parallax barrier was demonstrated for large panels with wide viewing angle and multi-view, but still kept acceptable 3D resolution and light efficiency. However, as mentioned in 5.2 and Fig. 6-1, the average crosstalk in the four-directional temporal backlight prototype was over 15% due to alignment between LEDs, lens, and prism. The distance between the LED backlight and the dual directional prism also caused vertical crosstalk, as shown in Fig. 6-2. Therefore, in Fig.
6-3, by covering the LED backlight with the dual directional prism to improve distance and alignment between the LED backlight and the dual directional prism.
Therefore, four viewing zones will also be produced with low horizontal and vertical crosstalk.
Number of views 3D image Resolution Light efficiency Parallax barrier 3D
display (Sharp) Lenticular lens 3D
display (Philips) Time division parallax barrier 3D display (Samsung)
53
Fig. 6-1 Comparisons between simulation and experiment.
Fig. 6-2 Vertical crosstalk phenomenon.
0
Viewing angle (°)
Source 1
Average crosstalk = 15% Average crosstalk = 35%
Micro prism 1
Alignment between LED, lens and prism cause light leakages.
Viewing angle(degree)
54
Fig. 6-3 Solutions to horizontal and vertical crosstalk.
Finally, because the proposed backlight produces four viewing zones sequentially at 240Hz, the LC response time in the proposed 3D display is also 240Hz.
Therefore, the response time of LC must be lower than 2ms. One solution is using OCB (Optically Compensated Bend) mode LC [25] [26]. Because there is no backflow while changing state in OCB mode, the response time is from 5ms to 1ms.
OCB mode also has ease of fabrication and wide viewing angle due to the self-compensated property. Another solution is Blue Phase mode LCD [27] [28]. Blue Phase is liquid crystal phase that appear in a temperature range between the cholesteric phase and the isotropic phase. The electro-optical response time at room temperature
D
D’
D: Distance between LED backlight and dualdirectionalprism D ,Alignment error and Vertical crosstalk Sequential LED plate
Cylindrical lens Dual directional prism
Diffuser
Sequential LED plate Cylindrical lens Dual directional prism
Diffuser
55
is 0.1 ms for the stabilized Blue Phase. Furthermore, because the Blue Phase mode can make alignment layers, the mechanical pressure sensitivity and the manufacturing steps are reduced. In SID 2008, Samsung developed the first Blue Phase LCD with 240Hz refresh rate. Therefore, by combining the four-directional temporal backlight and the multi-view parallax barrier with an OCB LCD or a Blue Phase LCD, the spatial-temporal hybrid multi-view 3D display will be fabricated.
However, in the synchronization between the sequential backlight system and 240Hz LCD, if LEDs turn on too early or turn off too late, the spatial-temporal hybrid multi-view 3D display produces distorted 3D images due to the temporal crosstalk phenomenon, as shown in Fig. 6-4.
Fig. 6-4 Temporal crosstalk in the synchronization between the backlight and LCD.
Therefore, in Fig. 6-5, the tstart and tstop are defined in the backlight synchronization. By adjusting values of tstart and tstop, for example, the observer standing at position 2 can’t see the frame 1 images and frame 3 images. So the temporal crosstalk is reduced and the 3D display present clear multi-view 3D images satisfied the simulation and experiment results mentioned before. However, periodic structure of the parallax barrier and the LCD cause moiré pattern in 3D images, as shown in Fig. 6-6. Therefore, the slanted parallax barrier design is also a vital work in the future.
Turn on too early Turn off too late
56
Fig. 6-5 Solutions to the temporal crosstalk phenomenon.
Fig. 6-6 Moiré phenomenon caused by the parallax barrier and the LCD.
t start ≒ t TFT+ t LC
Frame 1 Frame 2 Frame 3 Frame 4
t start
t stop t on
t stop = t start+ t on Reduce temporal crosstalk LED 1
LED 2
LED 3
LED 4
3D display
Position 1 Position 2 Position 3
Position 4
F3F2 F2
F1 F2
57
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