Principle Of Fiber Optics

- Jul 12, 2017 -

Folding light and its properties Optical fiber Light is an electromagnetic wave

     The visible part of the wavelength range is 390 ~ 760nm (nanometer). The greater than 760nm part is infrared, less than 390nm is ultraviolet. The application of optical fiber is: 850nm, 1310nm and 1550nm. 2. Light refraction, reflection and total reflection.

     Because light travels at different speeds in different materials, light is refracted and reflected from one material to another, at the interface of the two substances. Moreover, the Angle of refractive light varies with the Angle of incident light. When the Angle of incident light reaches or exceeds a certain Angle, the refractive light will disappear and the incident light is reflected back, which is the total reflection of light. Different substances have different refractive angles for the same wavelength of light (that is, different substances have different refractive index), and the same material has different angles of refraction for different wavelengths of light. 

Optical fiber communication is based on the above principles. 

1. Fiber optic structure:

   Bare fiber optic fiber is generally divided into three layers: central high refractive index glass core (core diameter is commonly 50 or 62.5 microns), middle to low refractive index silicon glass cladding (125 microns in diameter), the outside is to strengthen with the resin coating. 

2. Fiber optic numerical aperture:

   The light from the incident to the optical end of the optical fiber cannot be transmitted by the optical fiber, only the incident light within a certain Angle can be used. This Angle is called the numerical aperture of the fiber. The numerical pore size of optical fiber is beneficial to the connection of optical fiber. Different manufacturers produce optical fiber with different numerical aperture (AT&T CORNING). 

3. Type of optical fiber:

    There are many types of optical fibers, and different functions and performance are required. But for cable TV and the optical fiber, the principle of design and manufacture is basically the same, such as: loss is small; There is a certain bandwidth and a small dispersion; The wiring is easy; It is easy to be unified; High reliability; It is easier to manufacture; It's cheap and so on. The classification of optical fiber is mainly from work wavelength, refractive index distribution, transmission mode, raw material and manufacturing method. (1) working wavelength: uv fiber, appreciable optical fiber, near-infrared fiber, infrared fiber (0.85 mu m, 1.3 mu m, 1.55 mu m). (2) distribution of refractive index: step (SI) type optical fiber, near step type optical fiber, gradient (GI) type optical fiber, others (such as triangle, W type, concave type, etc.). (3) transmission mode: single mode fiber (including polarization to maintain optical fiber, non-polarization to maintain optical fiber), multi-mode optical fiber. (4) raw materials: quartz fiber, multi-component glass fiber, plastic fiber, composite fiber (such as plastic wrap, liquid fiber core, etc.), infrared materials, etc. According to the covering materials can be divided into inorganic materials (carbon etc.), metal materials (copper, nickel) and plastic. (5) manufacturing methods: pre-plasticised have vapor phase axial deposition (VAD), chemical vapor deposition (CVD), etc., such as Rod intube and double crucible method.