The origin and development of laser

The light source required for fiber-optic communication should be a high-speed modulated light source to carry large-capacity information. Such as lasers and LEDs. The so-called “modulation” is to change the intensity of light, etc., according to the information to be transmitted, to carry information. In 1960, Maimen invented the ruby ​​laser. The difference between laser and ordinary light is that the laser has a very simple optical frequency and has a linear line. In optical, it is called coherent light, and it is most suitable for light source of optical fiber communication. The usual light frequency is very messy and it contains many wavelengths. The usual light frequency is very messy and it contains many wavelengths. The characteristic of coherent light is that the light energy is concentrated, and the divergence angle is small, which is approximately parallel light. After the invention of the ruby ​​laser, various lasers were born: gas lasers, such as helium neon lasers; solid-state lasers, such as YAG yttrium aluminum garnet lasers; chemical lasers; dye lasers. Among them, the semiconductor laser is most suitable for the light source of optical fiber communication. Its small size and high efficiency, its wavelength is suitable for the low loss window of the fiber. However, the manufacturing process of semiconductor lasers is very complicated, and it is necessary to epitaxially grow five layers of doped semiconductor on a substrate material of extremely high purity and defect, and then lithographically illuminate the micron-sized optical waveguide thereon, which has a difficulty compared with the optical fiber. Nothing more than that. In the late 1970s, a semiconductor laser with a long working life at room temperature was finally produced. In 1976, the world’s first practical fiber-optic communication line was established in Atlanta, USA. At this time, the semiconductor laser has not passed, and the light source is a semiconductor light-emitting tube. In the early 1980s, single-mode fibers and lasers were mature, and the superiority of fiber-optic communication capacity was gradually brought into play.
The light emitted by the semiconductor laser is pure, the energy is concentrated, and the beam is very thin. It can efficiently shoot into a single-mode fiber with a core diameter of only 8 microns. Today’s high-speed fiber-optic communication systems use semiconductor lasers as light sources.

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