What is the basic principle of optical fiber guiding light? Optical fibers have different structural forms. At present, most practical optical fibers are composed of two concentric circles, namely "core" and "cladding".

In order to conduct light waves, the refractive index of the fiber core (n1) must be slightly higher than that of the cladding (n2). Why does it have to be this way?

First of all, light wave is a kind of electromagnetic wave, which has the general property of electromagnetic wave, namely wave. The wavelength of light waves is on the shorter side of the electromagnetic spectrum, and thus has its "personality", that is, the propagation of light waves is closer to the form of "rays".

Now we use the theory of ray optics to explain the physical phenomenon of light wave propagation in optical fiber. This method is not complete, but it is simple and intuitive. Ray optics is an analytical method in which the wavelength of light is very short compared to the size of the fiber, and ray is used to represent the transmission route of light energy. Ray optics is also known as geometric optics. It has three basic laws: the law of light's linear propagation, the law of light's reflection and the law of light's refraction.

The linear propagation law of light is that light travels in a straight line with a certain speed in a uniform medium. Propagation speed of light wave in vacuum: C=3×108M/S; Velocity of light wave in other media: v=C/n. Where n is the refractive index of the medium. In air, since n≈1, the propagation speed of light wave is close to C. Silica (SiO2) glass has a refractive index n≈1.5.

The law of light reflection is that light will be reflected when it hits the interface between two media during its propagation, and the Angle of reflection is equal to the Angle of incidence.

The law of light refraction states that as light moves from one medium to a second, its direction of travel changes.

Because we use the principle of total reflection to limit the light energy in the optical fiber, the refractive index of the fiber core material must be greater than that of the cladding when making the fiber, so as to ensure that the light wave propagates along the fiber core in the fiber.