The working principle of liquid crystal display

  We need to have a white light source that vibrates in all directions, and let it pass through a linear polarizer to become linearly polarized light that vibrates in only one direction. This linearly polarized light transforms natural light into linearly polarized light. In this light wave, less than 50% of the initial value passes through the polarizer. Then enter a medium with birefringent properties. This medium has a slow axis and a fast axis. When light waves enter this medium, there will be a component along the slow axis and a component along the fast axis. When the light wave passes through this medium, we will see the rotation of the polarization plane mentioned earlier. The polarization plane of the light wave before entering the medium is the direction of the linear polarizer, but due to the birefringence of the liquid crystal, before it exits the liquid crystal layer, its polarization plane direction has been rotated by a certain angle by the liquid crystal. At this time, if there is a polarizer called an analyzer optically on the other end of the liquid crystal layer, part of the light wave will be absorbed. The light wave can also be divided into two mutually perpendicular components, one component is parallel to the direction of the analyzer, and the other component is perpendicular to it. Of course, the component perpendicular to the direction of the analyzer will be absorbed, while the other component passes through the analyzer. From this we get the light wave passing through the second polarizer. The vibration direction of this light wave is the same as the original vibration plane, but its amplitude is reduced due to partial absorption.

  It can be seen that if we find a way to modulate the angle of rotation of the light wave in the liquid crystal layer to 90°, then the light wave will be completely absorbed at the second polarizer, which looks like a dark field from the outside. If the polarization plane of the light wave is not rotated at all, it will completely pass through the second polarizer,.