Optical Fibers

Optical fiber is a device that is working on the principle of total internal reflection and is used for transmission of signals, with negligible loss of energy. The optical fiber consists of a thin fiber of glass, silica, or plastic, having a high refractive index known as the core. The diameter of the core is variable from 10-100 micrometers. Often the core is enclosed by the cover of plastic or glass, called cladding. The refractive index of the core is greater than the refractive index of the cladding. The difference between these two indices is extremely small and is 10-3. Both the cladding and core are enclosed in the outer plastic jacket for protection purpose, that also gives strength to the optical fiber.

Working of Optical Fibers

When a light ray is an incident at the core of the optical fiber, at the small angle, then it is suffering from refraction that is striking the interface of core and cladding. Due to the small diameter of the fiber, the angle of incidence is greater than the critical angle. Because of this reason, the ray is suffering from the total internal reflection at the core-cladding interface and then it is striking the opposite interface. Again, at this interface, the angle of incidence is greater than the critical angle, so it again has to suffer the total internal reflection. In this, the light ray is reaching the other end of the fiber after repeated sufferings of the total internal reflection, throughout the length of the fiber. When the light ray is reaching at the other end of the fiber, then it suffers the refraction and finally emerges out. The traveling of light in the core is in a well-guided manner, so the process of communication through the optical fiber is also referred to as the optical waveguide. The degree of attenuation over the different distances is dependent on the composition of fiber and wavelength of light.

Types of Optical Fibers

Based on the refractive index, mode of light propagation, and material used the optical fibers can be categorized into different types. Based on the refractive index, the optical fibers are divided into step-index fibers and graded-index fibers. The classification based on the use of the material has given rise to two types such as glass fibers, and plastic optical fibers. Optical fibers are also classified based on the mode of propagation of light, into single-mode fibers, and multimode fibers.


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