Optical fiber is the abbreviation of optical fiber, which is a kind of fiber made of glass or plastic and can be used as a light transmission tool. The transmission principle is "total reflection of light". Kao Kun, former president of the Chinese University of Hong Kong, and George A. Hockham first proposed the idea that optical fiber can be used for communication transmission. Kao won the 2009 Nobel Prize in Physics for this.

Optical fiber is a kind of thin and soft solid glass material, which is composed of fiber core, cladding and coating, and can be used as a light transmission tool.

Fiber core: It is located in the center of the optical fiber and consists of high-purity silicon dioxide, i.e. glass.

Cladding: It is located around the fiber core, and its composition is also high-purity silicon dioxide. The cladding provides reflective surface and optical isolation for optical transmission, and plays a certain role in mechanical protection.

Coating: the outermost layer of optical fiber, composed of acrylate, silicone rubber and nylon. The coating protects the optical fiber from water vapor erosion and mechanical abrasion.

The realization of optical fiber communication is based on the principle of total reflection of light. When the light enters the fiber center for propagation, the refractive index n1 of the fiber core is higher than that of the cladding n2, while the loss of the fiber core is lower than that of the cladding. In this way, the light will have a total reflection phenomenon. Its optical energy is mainly transmitted in the fiber core. With the help of continuous total reflection, the light can be transmitted from one end to the other.

Working principle of optical fiber: at the transmitting end, the information to be transmitted (such as voice) is first converted into an electrical signal, and then transmitted to the laser beam through the laser. The intensity of the light will change with the frequency of the electrical signal and be transmitted through the optical fiber. At the receiving end, the detector receives the optical signal and converts it into an electrical signal, and the original information is recovered after processing.

The optical fiber made of glass fiber inside the optical fiber can transmit optical signals thousands of kilometers away, combine hundreds of thousands of optical fibers together, and make optical cables like imaging cables. This not only improves the strength of optical fibers, but also greatly increases the communication capacity.

The propagation speed of light in different substances is different, so when the light is transmitted from one substance to another, the junction of two substances will be refracted and reflected, and the angle of the refracted light will change with the angle of the incident light. When the angle of the incident light reaches or exceeds a certain angle, the refracted light will disappear, and all the incident light will be reflected back, which is the total reflection of light.

The optical signal is transmitted to the destination through refractions in the optical fiber. The optical signal will disperse or attenuate after refractions. Therefore, the optical signal needs to be amplified every 50 kilometers.