Optical fiber is short for optical waveguide fiber. It is a fiber made of glass or plastic and can be used as a light transmission tool. Optical fiber for communication is a medium for transmitting light, and its main component is silica. Its structure can be divided into a fiber core with a higher refractive index, a cladding with a lower refractive index, and a coating on the surface.
塗覆層（塑料保護外套）：Coating (plastic protective coat)
包層：Cladding
纖芯：Fiber core
光纖結構示意圖：Schematic diagram of optical fiber structure
Optical fiber as the transmission channel of light mainly uses the principle of total reflection of light to realize the transmission of optical signals in it. The refractive index of cladding n2 > the refractive index of fiber core n1. 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. The light rays produce total reflection at the interface between the fiber core and cladding and forms a necessary condition for the light to be locked inside the fiber core for forward propagation. Even if the light passes through the curved route, the light does not exit the optical fiber.
In single mode fiber, only one mode of optical signal transmission is allowed at one time, and the loss is relatively small, so it can be used in long-distance transmission. At present, single mode fiber is used in FTTx deployment of the access network.
Multi-mode fiber refers to the transmission of multiple modes of optical signals at the same time, which are easy to interfere with each other, with large loss and short transmission distance. It is mainly used for short-distance optical fiber communication, such as in buildings or campuses, and the cost of multi-mode optical fiber transmission system (transmitter and receiver) is low.
單模光纖：Single mode fiber
多模光纖：Multi-mode fiber
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