Total reflection principle: Since the speed of light propagation in different substances is different, when light is shot from one substance to another, refraction and reflection will occur at the intersection of the two substances. Moreover, the angle of refracted light will change with the angle of 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.
Different substances have different refraction angles for the same wavelength of light (i.e., different substances have different refractive indices of light), and the same substances have different refraction angles for different wavelengths of light. Fiber optic communication is based on the above principle.
According to the principle of geometric optics total reflection, the rays produce total reflection at the intersection of the fiber core and the cladding, and form the necessary conditions to lock the light inside the fiber core to propagate forward, even after bending the routed light does not shoot out of the fiber.
