But How does an Optical Fiber works, what is the physical principal behind its working. First of all, unlike copper cable an Optical fiber uses light and not electricity to transmit digital information. The principal of working of fiber optic cable is Total internal Reflection (TIR) unlike drift of free carriers as in copper cable. In order to understand TIR first we should know what material it is made of.
A fiber cable is mostly made up of glass (silica). It has three distinct regions. The innermost is called Core, which is surrounded by Cladding, and both of which are surrounded by a protective covering called jacket. The jacket is made up of PVC and its only role is protection of underlying glass fiber and does not play any role in transmission of information. The core is of higher refractive index relative to the cladding. During manufacturing some impurities are intentionally doped in pure glass to vary its refractive index to make the core and the cladding region. So when light is incident from denser (core) to rarer (cladding) medium with angle of incidence greater than the critical it is reflected inside the core rather than refracting in the cladding. Thus the light ray incident at the core-cladding interface is trapped inside the core and reached the output end thus allowing the transmission of optical data.