1. Large-screen Television Vision Technology
Content:
Types of TV display system
Liquid crystals
Polarization of light
Light modulation through polarization control
Modulation and display devices

2. TV display Types
(Digital Light Processing)

3. Type of display

4. Cathode ray tube display

5. Color signal generation

6. Basic information of liquid crystal

7. Liquid crystals
The liquid crystals are one of the most fascinating material systems in nature, having properties of liquids (such as low viscosity and ability to conform to the shape of a container) as well as of a solid crystal. Their ability to modulate light when an electric signal is used has made them invaluable in flat panel display technology.
Liquid crystals have anisotropic properties similar to solid crystal because of the ordered way in which some of the constituent molecules are arranged. However, the liquid crystal have low viscosity and can flow. The liquid crystals are essentially a stable phase of matter called the mesophase existing between the solid and the liquid. The crystal is made up of organic molecules which are rod-like in shape with a length of ~ 20A A0. A perfectly ordered arrangement of such a molecule can lead to a solid crystal. On the other hand, at high temperatures, a (disordered) liquid state is produced.

8. Different types of liquid crystals
The orientation of the rod Iike molecule defines the "director" of the liquid crystal. The different arrangements of these rod-like molecules leads to three main categories of liquid crystals:
Liquid crystals
Smectic
Nematic
Cholesteric
Molecules within a layer are ordered
long-range orientation order is present
No well defined layer order
Long-range orientation order is present
Well defined order within layers
Long-range "twist" between molecules on each layer

9. Twisted liquid crystals
This type of liquid crystal systems are called twisted nematic and a total rotation of 90 can be produced. If the twist angle is increased to enhance the eflect, the film becomes unstable if normal nematic films are used. For example, if a twist of 270 is desired, the stable state is one with a -90 twist. However, if cholesteric liquid crystals are used in which there is already a built-in twist, the 270 twist is possible. Such structures are called supertwisted LC .

10. Wave propagation in crystals
We have seen that unlike the non-crystalline materials, there is a long range order in the arrangement of atoms in these materials which leads to anisotropic physical properties. In fact, light polarized along different directions will propagate with different speed, in general. These anisotropic properties are of great value in designing remarkable optical devices-both passive and active. Among passive devices that use the anisotropy of light propagation in crystals are quarter wave plates to alter polarization, polarizers, birefringent plates, etc. The active devices that use anisotropy of the material are electro-optic devices, liquid crystal devices, acousto-optic devices, etc. The case of most interest to us is the uniaxial medium which describes most electro-optic devices used for light modulation and which describes the liquid crystals.

11. Wave propagation in crystals
If, in a uniaxial crystal, light is propagating in a direction other than the optic axis, a phase delay will develop between the two polarizations of light due to their different polarization velocities. This phase delay is exploited for designing devices that can alter the polarization of light. If somehow the refractive index can be altered, the device can become active and can be used to modulate a light signal.
If the wave is propagating along the z-axis (= 0), i.e, the optic axis, the value of nre() is simply nro as is expected. If the wave is propagating along the y-axis' nre() = nre
nrz=nre=extraordinary refractive index
nrx=nry=nro=ordinary refractive index