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Liquid Crystal Display (LCD) uses liquid crystal fluid as
the active medium to create images. As shown in
Fig. 1, a very large number of thin crystals suspended in a fluid.
The liquid reservoir is sandwiched between two thin layers of glass.
Each layer of glass has a transparent conductive electrode bonded
to it. |
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Figure #1 Polarizing material are placed on the outside surface of both front and rear glasses. The top polarizer can polarize the incident light of random polarization into its polarization direction. Before an electric field is applied on the conductors, the crystals are aligned in a spiral pattern. The light is then changed by the spiral pattern of the crystals. The bottom polarizer is aligned opposite of the top polarizer. When the light reaches the bottom polarizer, they will align with each other. The light can pass through and as shown in Fig. 2, the LCD looks transparent. |
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Figure #2 When in an electric field, the crystals align themselves with the field so the light can pass through the crystal without being deflected, as shown in Fig. 3. The light is then out of phase with the bottom polarizer when the light is absorbed by the polarizer. The light can't pass through and the LCD looks dark or opaque. By turning on/off electric field, we can create desired display patterns. |
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Figure #3 LCD technology is advancing rapidly. with the Super Twisted Nematic (STN), the display can reach a twist angle greater than 200 degree. |