From the black-and-white display at the end of 19 to the appearance of 1928 color TV and the color film shooting of 1935, the display technology has experienced a leap from black-and-white to color display technology, and is currently in the development period of digital display. Digital TV and digital movies based on modern digital technology are solving the problem of resolution and clarity of video images, including signal acquisition, processing, storage, transmission and reproduction. In the existing digital display terminal, the number of pixels can be increased from 720×480 in NTSC standard data to 3840×2 160, and the resolution can be improved by more than 20 times. However, the color reproduction ability of the existing display is very low, and its color rendering range can only cover 33% of the color space that can be observed by human eyes, while the other 67% of the color space cannot be reproduced by digital display technology and existing display technology. Therefore, the display technology that can achieve high definition and large color gamut at the same time will inevitably become the research and development direction of display technology. An important idea of laser display technology is that, from the chromaticity point of view, the display technology with red, green and blue (RGB) lasers as the light source can truly reproduce the rich and colorful colors of the objective world and provide more shocking expressive force, so laser display is called "the revolution in the history of human vision". Among many different display technologies, laser display technology represents the future development trend and mainstream direction of display technology, and is the focus of competition in the future display field. The earliest laser projection technology used gas lasers as light sources, such as He-Ne, argon ion, krypton and copper vapor lasers, which radiated red, blue and green lasers respectively to realize full-color laser projection, but the electro-optical efficiency of gas lasers was very low and the working reliability was poor.
Red, green and blue radiation can also be obtained by using all-solid-state laser pumped by laser diode and frequency doubling technology, and the continuous output power can reach several watts, dozens of watts or even hundreds of watts. These all-solid-state lasers have high electro-optical efficiency and stability and compact structure, and a few watts of power can be used for laser projection.
The visual function values of red, green and blue are quite different, which are 0.265(630nm), 0.862(530nm) and 0.09 1(470nm) respectively, so the laser power should be matched. There are many ways to realize laser projection, among which polyhedral rotating mirror scanning and vibrating mirror scanning are commonly used scanning devices.
Polyhedron rotating mirror scanning. The polyhedral matrix is made of light metal material. In order to reduce the moment of inertia, plane mirrors are fixed on the polyhedron, and the angle of each plane mirror in the Y-axis direction is adjusted, so that the straight lines are separated at equal distances, thus realizing field scanning. Polygon rotating mirror scanning has great limitations, for example, the fewer scanning lines, the lower the resolution and the more planes, the more difficult the adjustment is.
In galvanometer scanning, high-performance galvanometer is used to drive the plane mirror to deflect at high speed and locate accurately. Because the deflection frequency is extremely high, just like vibration, it is called vibrating mirror. Two-dimensional scanning can be realized by using two vibrating mirrors.
More often, polygon rotating mirror and vibrating mirror scanning are used at the same time, which complete the scanning of lines and fields respectively.