For the proposed structure, the transmission of the PDLC component, LC panel, and projection lens are 78%, 5.3%, and 66%, respectively. Thus, the total transmission of all system is only 2.7%, and the projection image brightness is about 1 lumen.
Compared to the market-available mini-projector, the projection image brightness from our structure was lower than 10 lumens. The 10 lumens brightness is presented from mini-projector, as shown in Fig. 6-1. Beside, panel could project image directly by using projection lens structure. Thus, the projection lens should cover all panel region, and the projection lens diameter was about 50mm, as shown in Fig. 6-2. This size was not compact enough for mobile phone application.
Proposed device with projection function Market-available
mini-projector*
* Optoma PK101
Fig. 6-1 The image brightness difference between the current mini-projector and the proposed switchable device.
Lens diameter
~50mm Projection lens
element
Fig. 6-2 Projection lens diameter is about 50mm.
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In the future, the backlight module will be redesigned. To increase projection image brightness, the high power LED will be used. Also, the high power LED will provide 1 inch illuminated region, so that the projection lens size can be reduced. For the image brightness requirement of 10 lumens, the backlight module needs to provide 370 lumens brightness considering the transmission of the entire system. The illustration of the backlight is shown in Fig 6-3(a). During projection mode, the high power LED is turned on and provides projection backlight with the size of 1 inch in diameter. The projection image will become brighter, as shown in Fig. 6-3(b). While during direct view mode, the LEDs which are located at the side edge of the light guide are turned on along with high power LED and provide divert view backlight with the size of 2 inch in diameter. Thus, the direct view image will become more uniform, as shown in Fig. 6-3(c).
In addition, increasing the transmission of the entire system is another method to improve the projection image brightness issue. Therefore, the FSC method [24] can be used to increase transmission of LC panel. By FSC method, LC panel does not use color filter, and the LC panel transmission can be enhanced about three times. Thus, the transmission can achieve to about 15%. Besides, the projection lens and PDLC transmission are able to be improved by using the glass materials. Then, the transmission of the entire system will be enhanced. By calculating, the transmission of the all system can achieve about 8%. For the image brightness requirement of 10 lumens, the backlight module only needs to provide 125 lumens brightness. The 125 lumens brightness can be also presented by the high power LED which provides the 1 inch illuminated region, and the backlight module is shown in Fig. 6-3(a). Therefore, the transmission of entire system can be increased and the brightness is also enhanced.
Due to the modification of backlight, switchable device will be also modified. In
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direct view mode, 2 inch panel is used to show the direct view image, as shown in Fig.
6-4 (a). Then, 1 inch central area of the panel is used to project image in projection mode, as shown in Fig. 6-4 (b). Therefore, the projection lens size can be further reduced to be fit into mobile phone. Consequently, the projection image brightness, and projection lens issues can be overcome.
LED
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LED
High Power LED
Light‐guide LED
LED
High Power LED Reflector
LED
LED
LED
LED LED
(c)
Fig. 6-3 (a) Sketch of the redesign backlight module, (b) 1” projection backlight, and (c) 2” direct view backlight (the yellow color region in figs. (b) and (c) are illuminated region).
2” panelfor direct view mode
Projection image
1” panelfor projection mode
(a) (b)
Fig. 6-4 (a) 2” panel for direct view image, and (b) 1” panel for projection mode.
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