The fundamental principle behind optical fibers is a physic phenomena called total internal reflection. In order to have total internal reflection, light has to get out from a more refringent (refractive) medium to a less refrigent one and the angle of incidence must be equal or greater than the limit angle (also known as Brewster angle).

Figure 1: Example of an optical fiber.

Optical fibers are basically made of dielectric (insulating) materials that, as we already mentioned, allow complete imunity to electromagnetic interference, having two areas, a center region called core, where the light pass through, and an external region called cladding which covers the core. The refracting index of the material used on the core is higher than the refracting index from the material used on the cladding.

On Figure 2 you can see the anatomy of an optical fiber.

Figure 2: Anatomy of an optical fiber.

Here is the description of each part of the optical fiber:

• Core: The core is a thin filament made of glass or plastic, measured in micra (1 mm = 0,000001m), where the light pass through. The larger the diameter of the core, the more light it can conduct.
• Cladding: Layer that revests the core. Since it has a refraction index lower than the core, it prevents the light from being refracted, hence allowing the light to reach the reception device.
• Plastic buffer: Plastic layer that revest the skin, protecting the optical fiber from mechanical shocks and excess of bending.
• Mechanic resistence fibers: Fibers that help to protect the core against impacts and excessive tensions during their installation. They are usually made of a material called kevlar, the same used on bullet-proof vests.
• Outer jacket: Is the jacket that covers the optical fiber.