The fact that light can be transmitted in glass fibers or plastic fibers is based on the principle that light produces "total reflection" at the interface of two substances with different refractive indices. In order to prevent the "leakage" of light during the transmission process, the glass filament must be put on a "coat", so whether it is a glass optical fiber or a plastic optical fiber, the core wire is mainly composed of 

and the cladding are composed of two parts. The structure of the optical fiber is cylindrical, with a core with a diameter of 8 microns or 50 microns in the middle, which has a high refractive index, and is covered with a low refractive index cladding. The advanced manufacturing process and special materials make the optical fiber not only slender and flexible like silk, but also have high strength and high pressure resistance.

Since the refractive index of the cladding is smaller than the refractive index of the core wire, the light entering the core wire undergoes multiple total reflections at the interface between the core wire and the cladding layer and then twists and forwards, and does not pass through the interface, as if the light rays are tightly bound by the cladding layer. The ground is enclosed in the core wire, so that the light can only be transmitted along the core wire, just as the tap water can only flow in the water pipe.

Light also has the characteristics of waves, so it can be equivalent to sound waves and transmit signals like electromagnetic waves. The whole work of the optical fiber is completed with the special receiving instrument and the transmission function of the fiber conduit.