How does fiber optics? – Propagation of light and total internal reflection’
An optical fiber has a core and a sheath. The core diameter of a single mode fiber is about 9 microns. But more than the geometric core, the diameter of the field mode (MFD) is important for the transmission by an optical fiber. The diameter of the field mode is the diameter of the range of movement of the light inside the fiber. It includes the core but also part of the coating.
The core and the cladding have different refractive indices. This means that light travels at different speeds in the nucleus and of the sheath. This difference is very small, but it is very important that the optical fiber carries light along its length. Due to this difference in refractive index between the core and the cladding, light surges to the core boundary and return hit to the opposite border, and reflect again. This total reflection process is called total internal reflection. Total internal reflection or TIR is the basic principle on which runs an optical fiber.
The core has a refractive index slightly higher than that of the cladding. Theories of light dissent that when light travels from a medium of higher refractive index to a medium of lower refractive index, the light is reflected. This total internal reflection is shown in the diagram below.
If n1 is the core refractive index and n2 is the refractive index of the cladding, then n1> n2 is the condition of total internal reflection.
Some references to the speed of light here will be useful to remember. The speed of light in vacuum is 300,000 km per second. If the light passes through a medium at a speed of 200,000 km per second, the middle refractive index is 1.5. The calculation is as simple as that. The refractive index is calculated by dividing the speed of light in vacuum by the speed of light in the medium.
Therefore, can be put in the form of a mathematical formula: Refractive index of a medium = speed of light in vacuum / Speed of light in the medium.
A total internal reflection took place and the light has traveled throughout the fiber carrying our voice, data, video and images. Hence the usefulness of this total internal reflection!.