Fiber is the abbreviation of optical fiber. An optical fiber is a kind of transparent filament with coating, usually composed of a core material (glass) and coating (glass). The core diameter of optical fiber ranges from several microns to dozens of microns, and the outer diameter of coating is of magnitude from 0.1 to 0.2 mm. The refractive index of the optical fiber coating must be less than that of the core material, and there should be good optical contact between the optical fiber core material and the coating to form a high-quality optical interface. When the light is incident at an angle of mouth on the incident end face of the optical fiber (Fig. 4.2.3-1), it enters the optical fiber after refraction, with an angle of φ on the smooth interface between the core material and the coating. As long as an appropriate angle of incidence θ is selected, the angle can always be larger than the critical angle required for total reflection φ m, and the incident light will produce total reflection on the interface; If the optical fiber is a uniform cylinder, the incident light can pass through several times (related to the length and diameter of the fiber, generally hundreds, thousands, or even tens of thousands of times) after total reflection in the optical fiber, and then it will be reflected by the optical fiber from one end to the other end until it is ejected from the exit end face.
Multimode fiber optic switch has advantages of long service life, safe and reliable, strong anti-interference, especially suitable for humid, high temperature, strong electromagnetic interference and other applications, multi-mode optical fiber switch can be completely immersed in liquid can, and it can also be installed far away from the control system.